Intro to Mosaicking

Introduction

This short report refers to a specific procedure taking part on the Balloon Mapping Project, where aerial images from the University of Wisconsin - Eau Claire (UWEC) campus were taken with a simple camera elevated by a helium balloon. Individual images are interesting but to see all of the images put together can give a much better view of the location.

It’s possible to do that in a number of ways, such as using MapKnitter, ERDAS Imagine and Arc Map. In a first hands-on the procedures, the software used didn’t matter much, but in this second activity, Arc Map was focused. The class worked together dividing tasks equally over the campus, and the result should be an update imagery for UWEC campus.

Methods

The very first step is to select the best images to be used. Since the camera can be tilt and not necessarily in the perfect focus, an analysis of the more vertical and clear is essential to have better results (Figure 1). Also, the images need to have an overlap between each other of at least 60% and cover the entire campus.

Figure 1 – Oblique Vs. Vertical Images

Although intuitively the next step seems to be just to put everything together and match, when you take simple pictures with a camera, they are not georreferenced, so a mosaic tool wouldn’t work at this point. Therefore, the Georreferencing tool in Arc Map is used to give the right coordinates to the points over the image (Figure 2). The accuracy is improved as much control points are added, so a minimum of nine points per image was established.

Figure 2 – Georreferencing

After the images are correctly georreferenced, it’s time to put them together. In this step, an important point is to figure out the order of the images: the best images should be on the top, and the worse on the bottom. Also, it’s necessary to try different ways to avoid the string between the balloon and the ground (Figure 3), working with images taken in different angles. Then, the Mosaic to New Raster tool is used to produce the mosaicked image.

Figure 3 – Presence of string in the images.

Since this process is time demanding, the 18 students in this class divided the tasks to increase the efficiency and quality of the results: if each students have less images to be georreferenced, it’s possible to do it more carefully and with a higher precision. Therefore, the campus was divided into six areas, where groups of three would work in (Figure 4). For our group, five images were georreferenced for each one, and then mosaicked.

Figure 4 – Campus divided in 6 evenly polygons.

Discussion

Precise ground points were collected to improve accuracy when georreferencing, however, all of them are located in lower campus, while the section taken by the group was in the upper campus. Therefore, both imagery and the buildings feature class could be used as a reference. The buildings feature class didn’t match with the imagery though, probably because of a distortion in the imagery (Figure 5).

Figure 5 – Buildings feature class Vs. Imagery

Although the best would be to stick with the most precise – the buildings – there were some areas where there were not enough building corners (Figure 6), so the imagery would have to be used. Using two sources as a reference that doesn’t match each other was not a good idea, so only the imagery was used.

Figure 6 – Area lacking in building to use as ground control points.

When the five images chosen by each component of the group were ready, they would be grouped as a layer to ease the use of transparency and maintain organization (Figure 7). In that way, it was possible to analyze both imagery and pictures at the same time.

Figure 7 – Transparency Settings

The control points were focused in the area where each component was responsible for, since the same area – not completely accurate – would be overlapped by a better georreferenced image. After the georreferencing were completed by all the components, the mosaick to new raster tool could be directly used from the JPG, without the need of exporting it as a raster dataset.

Conclusion

The georreferencing activity can be time-demanding and require attention to detail, which can make it a really hard procedure to be done for the entire campus. However, the division between all the classmates allowed this activity to be efficient and productive.

It was also an interesting activity since the class needed to use their own resources and talk to each other to learn how to use the tools and the theory behind each procedure. More in this section will be covered in the final report for the Balloon Mapping Activity, where each step for the entire project will be explained.

Final Field Navigation

Introduction

Navigation is basically the mains one uses to locate from one place to another. That can happen in many ways and it’s a common task from the day-a-day: when you use a car GPS to give you the routes from home to work or in a trip, when you give the directions to someone at the streets. It’s more crucial when dealing with transportation by air or water, where small mistakes can have big consequences. It’s also one of the reasons why geography had extreme development when the European countries started to explore the “New World”, centuries ago.

The typical navigation requires the knowledge of the points you want to get, in a given coordinate system. The way to get to this point can be divided in two main ways: the traditional, counting on a compass and pace count; and with a GPS unit. In both ways, a map with the main features can help the identification of the main elements in the surrounding area.  In this project, all these mains will be explored and tested.

Firstly, the map is produced as a way to be a reference support to the reader, who can interpret it and potentiate the knowledge about the area one is. Therefore, map production includes a clever selection of the appropriate elements for reference, as well as dealing with different levels of emphasis in each of them. Then, the use of a compass can provide the true direction where one needs to go, while the pace count will provide de distance walked. Alternatively, the GPS unit can provide both elements automatically updated as you walk. The comparison of all the methods and the understanding of the issues related to all the processes will provide a productive analysis of navigation methods.

Study Area

The navigation exercises were done at The Priory (Figure 1), a property with 112 mostly wooded acres and three building complexes, having approximately 80 thousand square feet. It was bought in 2011 by the University of Wisconsin - Eau Claire, it is located three miles south of it, in the town of Washington. (UWEC, 2013).

Figure 1 – Aerial Image of The Priory, by Google.

Besides the constructed area, where a recreational and educational center is located, a large open area was available for the exercises, containing three courses. The courses intersect each other, containing five points each where an orange flag is located (Figure 2). The activities were done during the month of March, so the area was entirely covered with snow in a high depth. Also because of the season, the extremely dense woods didn’t have any leaves, so the mobility through the areas was challenging (Figure 3). However, some trails were available, although hard recognizable due the amount of snow. Since part of the exercise includes the use of paintball equipment, some areas were considered restricted, where it was totally prohibited to engage in any type of shooting.

Figure 2 – Courses at The Priory

Figure 3 – Weather Conditions at The Priory

Methods

The complete project totalized four weeks: preparation and planning in the first week; navigation on site with compass and map in the second week; navigation on site with a GPS unit, but no map; and for last, navigation with GPS unit and a map.

During the first week, the area was analyzed by gathering data related to elevation, dealing with the digital elevation model – obtained by USGS – as well as a two feet contour line – surveyed by the University of Wisconsin – Eau Claire, at the moment the purchase of the property was done. Other elements for the area, such as buildings and vegetation density could be examined by the imagery obtained by the Wisconsin Regional Orthophotography Consortium (WROC) in 2010. The map production should be then made thinking of the reference features that could support the navigation on site.

Also for the first week, the pace count was made to provide the distance element for the traditional navigation. Using a laser device, a 100 meters line was placed on the sidewalk using snow (Figure 4), where the students could walk numerous times counting steps, until an average step size could be calculated.

Figure 4 – Calculating Distance for Pace Count with Laser Device

In the second week, the class could then go to The Priory for the traditional navigation. The points’ coordinates were given and plotted in the map (Figure 5). The class was instructed on how to use the compass, both to take the azimuth value from the map and how to navigate with it.

Figure 5 – Point plotting and azimuth taking using the compass.

A table was made containing initial point, final point, azimuth value and distance between the points. Although it would be useful to have the actual distance between the points in “step” units, accordingly to the pace count of the person who would be the walker; time didn’t allow these measurements, so the distance was actually being taken during the navigation itself.

Then, in groups of three, one would calculate the azimuth with the compass, the second would be the target for the compass, since the trees were too similar to be used as a reference, and the third would walk counting steps. Also, the frequent analysis of the map would provide recognition of the place the group was.

For the third week, the only resources for the navigation would be an Etrex GPS unit, along with a table with the coordinates. To find the points, there are two techniques: one way is to constantly look at the given coordinates on the GPS and observe how they change while you walk. Then, you can fix the X coordinate by walking in a certain direction, and then the Y coordinate in a different direction. However, this method is not very efficient, since you don’t take the fastest way. Then, to go around this problem, a tool in the Etrex unit could be used. There, you input the coordinates of the point you want to get, and then a compass in the screen shows the direction, as well as the distance left. This is pretty in handy since the distance and direction is automatically updated as you walk, so it’s possible to take easier paths instead of being inside the woods all the time.

For last, the fourth week consisted on the navigation with the Etrex GPS unit and a supporting map. Then, the map production was done again, including new features like course points – which were used to create also the lines between them – and the restricted zones, where the use of paintball equipment was not allowed.

The idea is that the groups would try to slow down others by attacking them with the paintball equipment, the penalty for being hit was two minutes stopped for the entire group. The first group who took all the course points would win. Despite the game perspective, the idea was to test the efficiency of the use of a GPS unit along with a supporting map, even with the weather challenges and rival groups.

For both exercises including the GPS unit, the track log was turned on during the activity to represent the path taken by each individual. Although in the first week no pattern was established for the collection, all the units should be set to collect point features every 30 seconds in the final week. The analysis of these paths could show interesting elements.

Discussion

During the exercise, some issues were faced and corrected or understood, allowing the group to use this experience to avoid the same problems in the future.

                Data Source Information

At the first step – map production – one of the features – the two feet contour line, obtained by UWEC survey – didn’t have a defined projection. That means that the features contain coordinates, but the coordinate system referred to this coordinates is not attached to the file. Therefore, depending on the current projection applied to the data frame, the feature will be located on-the-fly, accordingly.

However, if the data frame projection is not the same as the feature, the on-the-fly will locate the feature far off the correct place. In the situations, it’s necessary to first analyze the data source, where the appropriate coordinate system should be available. If not, an important troubleshoot method is to analyze the information on the feature extent (Figure 6) and compare the possible units and distance to the main coordinate systems used: Geographic Coordinate System, Universe Transverse Mercator, State Systems, State Plane Systems and, in some cases, even County Systems. Special attention should be taken on the different datums: even after finding the correct coordinate system, the use of an incorrect datum can place the feature far off.

Figure 6 – Extent of the two feet contour line feature.

During the troubleshooting, it’s essential to pay attention to the tools used to test, “Define Projection” should always be used and not confused with “Project”. The first tool will simply label the coordinates with a coordinate system, while the second will change the coordinates accordingly with the projection chosen. It is best practice to work with features in the same coordinate system, so the project tool should be used later, however, a feature can only be projected after it is labeled.

                Navigation Coordinate System: UTM vs. GCS

The maps were first produced in the Universe Transverse Mercator (UTM) coordinate system with a 20 meter gridline. However, the first activity consisted in using the map along with a compass; therefore, the appropriate coordinate system for this specific purpose should be the Geographic Coordinate System (GCS).

The compass points to the true north, which only GCS has. As noticed in the Figure 7, maps in UTM have parallel gridlines equally distant, because it’s a projected coordinate system. In the real world, the closer you are from the pole, the closer the gridlines should be from each other – which happens in the GCS. Since the area of interest is small, the difference is almost indistinguishable; but it’s important to be aware of this problem because it can have complicated consequences when dealing with large distances.

Figure 7 – Gridline difference between UTM and GCS.

                Compass Trust

Since it is an old school technique and the GPS took its place everywhere, the compass is commonly put in doubt by the ones who are used to other techniques. For that reason, the group couldn’t find one of the points in the first activity.

The reasons for doubt were legit: there was, indeed, a lack of precision depending on how many times the group would stop, because if one error is done in the beginning, it’s carried on with others, accumulating. The magnitude of the error was misinterpreted: this kind of error would take the group something like one or two degrees of the track, which in a small distance doesn’t mean much.

Therefore, it’s necessary to trust the compass and not to exaggerate possible errors while navigating; they do exist, but wouldn’t compromise the activity. It’s important to find a balance of precision awareness. Of course it’s important to be precise and find the right locations, but when you get too worried about small errors, it might cause more confusing than be a helpful attitude.

                Contour Lines Interpretation

After not finding the point with the compass and starting thinking on a direction errors, the map was used to analyze the features surrounding the group. Since the area was mostly full of trees, the best reference was the elevation.

The group was close to a ravine, so the contour lines would help to find the point. However, due to a quick analysis of the map, the contour lines were misinterpreted. The point was located on the bottom of the ravine, but the group was certain that it would be on the top of the ravine. A later analysis of the maps allowed to notice that the map was actually showing the bottom, not the top (Figure 8).

Figure 8 – Ravine analysis by contour line.

The contour lines were part of the map to support the area identification, and they would be really useful if the correct analysis was made. A lesson comes with that: only put information in a map if the reader is able to understand and interpret it correctly, otherwise it can be more confusing than helpful. The users in this case were knowledgeable about the interpretation of contour lines, a more careful reading was necessary though. However, it's important to understand this idea in general contexts, other than this activity: if something is supposed to be released for the public, it might not be a good idea to insert technical concepts and features.

                Weather Preparation

As said before, the activities took place during a cold winter, inside densely wooded vegetation where the snow depth was commonly higher than 50cm. In these situations, it’s essential to have the appropriate preparation. A number of layers are crucial to keep the temperature acceptable, but need to be thought in how it can limit your movement as well. The use of long boots and water-proof is also very useful because the snow can easily be melted and compromise even more how cold the individual will feel. Gloves are also extremely important, not only for the cold: since the trees don’t have their leaves, the branches can easily hurt your hand if you’re not protected.

Results

In the first activity, one hour was used for plotting points and taking azimuths, and the other two hours were only enough to find three points in the first course. As mentioned, the lack of effective in this case was not due the use of compass and map, but due the misinterpretation in the map reading and in the compass doubt. However, even if that was not present, this method is, indeed, more time demanding than others because it’s necessary to stop frequently.

For the second activity, in less than two hours it was possible to go through all the points in the second course and the exercise felt much more smoother than the first one, especially because of the use of the GPS function where you input the coordinates and it will automatically update the direction and distance you need to go. The track logs show how the group could take more pleasing paths with less vegetation and hills (Figure 9).

Figure 9 – Group track logs in the second activity

Lastly, the use of a map in the third activity improved even more the navigation. In this case, 10 points were found in an interval of approximately two hours and a half. The group missed five points, which was more related to the time consumed in the conflict zones, other than because of the navigation method. As it can be seen in the Figure 10, the circled regions have a higher amount of points and represent the times where our group found another group, resulting on a reasonable amount of time shooting until one of the groups would be out for two minutes.

Figure 10 – Third Week: Individual track log and conflict zones.

The same pattern can be noticed on the Figure 11, where the same areas contain a high amount of points from the entire group. Despite these conflict zones, the path taken by the group can be considered reasonable, since it wasn’t necessary to go back and a high amount of points was still covered.

Figure 11 – Third Week: Group track logs map.

When putting all the track logs together, for the entire class (Figure 12), it’s noticed that everyone could reach a high amount of points, if not all of them. Then, it’s possible to say that the most effective way to navigate was with a GPS unit and a reference map. However, it’s important to understand that it was the third time that the class went to the priory, so the place was already not that unknown, which surely support the navigation: it’s always easier to find yourself when the place is familiar. It doesn’t change the high efficiency in this case, but it’s an important element to keep in mind.

Figure 12 – Third Week: Class track logs map.

The presence of a map during navigation is surely helpful and increases the efficiency during navigation.  However, it depends on how the reader can take advantage of this resource: the elements in the  map have to be understandable for the reader and he or she need to have the necessary background knowledge in how to read it. If these elements are found, the map improves immensely the navigation, not only in this context, but in all the other day-a-day situations mentioned before, where navigation take place.

Conclusion

The project provided a rich experience both in technical knowledge as well as in field practice. It was incredible how many technical elements needed to be understood in favor to have a productive navigation activity. It was possible to improve troubleshooting skills, as well as a huge amount of self-evaluation which potentiate the learning obtained, by understanding the reasons for each issue faced. The experience in dealing with challenging weather conditions was also very important to focus the preparation section of any field work. Map making was also a big part of this project, which allowed exercising cartography and GIS skills.

By comparing all the methods for navigation, the use of a GPS is much more effective than the compass, but its precision can be compromised in locations where a compass wouldn’t. Then, the choice of which method is appropriate will depend on the purpose of the project and the area of interest.

Even though the GPS can have its precision compromised, the exercise took place in cloudy days inside a very wooded vegetation – a typical scenario where the PDOP gets higher and the accuracy goes down – and even though it worked very well. Then, in most of the situations, the use of GPS will provide enough accuracy and efficiency, especially with the technology improvements that keep happening in a high rate. Therefore, since a reference map is extremely helpful, the best method in most of the situations will be the use of a GPS unit along with a map.

References

UWEC. The Priory. Available in http://www.uwec.edu/Chancellor/priory.htm. Accessed on April 1^st, 2013.

Navigation Part III - GPS Unit

Introduction

For the navigation subject, the preparation before going to the field was already covered, and in the last week, the first field activity was done using the traditional method: map and compass. Now it’s time to deal with the use of a GPS unit for navigation. However, the map produced before won’t be available at this point. In the next exercise, though, not only the GPS unit will be used, but also an improved map for navigation. Finally, a comparison of all the methods along these weeks will be done.

This week’s activity, the navigation with the GPS unit, occurred on March 11^th, 2013 and the main goal was to analyze how well this technique works, comparing to the traditional way with a compass and map.

Methods

Considering the depth of the snow in the last activity and the permanence of the weather conditions, if not worse than before, it was necessary to improve the clothing preparation. Then, water-proof and a higher number of layers were used.

The only equipment used in this exercise is a Garmin Etrex GPS Unit (Figure 1), supported by a table containing the UTM coordinates for each point. After a quick overview about the basic use of the unit, each group was directed to the corresponding course.

Figure 1 – Garmin Extrex GPS Unit

This report refers to the procedures taken by the Group 1, who navigate by the course number 2, from the first point to the sixth point. The track log mode was turned on without any change in the settings. For the first points in the course, a method was applied to find them; and then another for the further points. The first consists in fixing one of the coordinates and, after that, fixing the other coordinate. This way takes a longer time, but would guarantee to arrive in the correct place. Then, the X coordinate was taken in consideration, and after being in the correct place in the X axis, the same was done to the Y coordinate. By looking at the changes in the coordinates on the unit screen, it was possible to guarantee that the direction was correct. The internal compass of the unit was also used to be certain of the direction.

However, after two points, it was noticed that a more convenient and effective way could be used to navigate from one point to another. The GPS contains a tool called “Where to?”; the coordinates for the target point are input there, and the unit will automatically show the direction on the compass and the distance to there. With this way, a lot of time was saved, and it wasn’t necessary to keep the eye on the GPS all the times, allowing to be aware of the environment around more carefully. Also, the direction and distance were automatically update as the group moved, so there were no worries about the lack of precision in case the track was missed because of some obstacle – such as elevations, dense vegetation or restricted areas. The precision was never perfect since the area consists in woods, but the margin of error, based on the PDOP, could be constantly monitored and kept in an acceptable level.

After passing through all the points, the tracklog was turned off and later downloaded in the computer. For that, it was necessary to examine the DNR Garmin software, connecting it to the GPS unit by an USB cable and acquiring the data stored in it. The data can be exported as a shapefile based on points or lines. The first choice was line, but later on it was known that the ideal type would be points. Then, Arc Tool Box was used, and the command “Feature Vertices to points” enabled the conversion from lines to points.

All the students were supposed to follow the same process and all the data would be available for the class. The files were located on a protected folder, reason why it was preferable to create a new geodatabase in the personal folder – where editing is allowed – and import the data (Figure 2). Besides the geodatabase, dataset were created to maintain organization and guarantee the coordinate system uniformity. In this case, the Eau Claire County System was used: since the tracklogs would be used only for presentation purposes, it was no longer necessary to use the UTM coordinates. In this case, the coordinate system covering the smallest area will have the minimum distortion and that’s why the county coordinate system was chosen.

Figure 2 – Geodatabase

However, as it happened before, some track logs were available as lines, so it was again necessary to run the “Feature vertices to points” command in Arc Tool Box. After having all the data prepared, three maps were elaborated: an individual map containing my own path in the activity; a group map referring to the tracks from each of the group components; and, for last, a map containing the paths taken for the whole class components.

The course points were also available, so they were added to all the maps and symbolized accordingly to the course they belong to. Also, it would be interesting to have an idea of the shortest path that could be taken between the points. For that, it’s necessary to create lines between the points. The command “Points to Line” in the Database Management in the Arc Tool Box was used to have this result. However, if it was simply run only inputting the source and output, there would be a connection line between all the points. That wouldn’t represent the idea of three different courses, as it’s needed. Then, the “Line Field” was use to indicate which field in the attribute table would differentiate the lines created.

Figure 3 – Use of Point to Line tool

Then, it was possible to symbolize both lines and course points accordingly with their course. Labels were also used to assess the readability of the maps. Different levels of emphasis were used depending on the map being made and the amount of data associated. Transparency and lighter colors were used when these features were not the main point of the map.

For the map with the track logs of all the students, they were separated in the corresponding groups and each group would have the same color to help the interpretation. However, when dealing with the group map, the three track logs were symbolized in different colors to analyze the differences and similarities between them. In this case, since the other courses were not part of the analysis, a higher scale focusing only in the second course was use. The same scale was used for the individual map, as well as a higher tone for the points and lines of the course, so a comparison would be easily done.

The maps were essential to support the analysis of accuracy and precision of different collections, as well as to notice different behavior taken in the path, depending on the obstacles found. The use of the satellite image was important to recognize different types of vegetation and its effects on the paths taken.

Discussion

In terms of accuracy, it’s interesting to examine the individual map (Figure 4). In the fourth course point, the GPS acquire some points close or even on the highway, where the group clearly didn’t go to. The same problem doesn’t occur in most of the other places and although the area was vegetated, it wasn’t much different for the others.

Figure 4 – Individual Track logs map

Thus, the most reasonable explanation for this lack of accuracy at this point is the fact that in the fourth course point, the group stopped for a moment to rest and set the GPS to the next point (Figure 5). The longer time at this point can be noticed by the high amount of points taken there. When dealing with a path, collection done by a GPS have the accuracy compromised when the GPS unit stays for a longer time in the same position. It’s different when collecting a point feature class, where the unit collects a number of points, ignore the outliers and calculate the average of the others.

Figure 5 – Quick stop to rest and set the GPS to the next point.

It’s also possible to notice that after the sixth point, the collection soon was stopped. That was not intentional, but the battery was low and after the sixth point, there was no much need of looking at the GPS so frequently, then it turned off automatically and this was only noticed later.

As well as in the last exercise – with the map and compass – the snow depth in this activity was really high (Figure 6), compromising how fast the group could move between points. Then, a tactic used was to avoid hills and dense vegetation areas – that would compromise even more. So, the natural trails were used as much as it was possible. This involves a higher distance, but would be more effective.

Figure 6 – Snow depth reaching Andrew’s knees.

This behavior taken in the paths can be notice both in the individual map, but also in the group map (Figure 7): all the track logs follow the contour lines, showing that there was not a high change of elevation by avoiding hills. Between the fourth and fifth point, the track taken was also longer than it could be, because an area closed by fences was being avoided. Another feature avoided was the dense vegetation at east, the group only got inside tit when it was really necessary to get to the point. To walk through it was complicated, so the trail was preferred.

Figure 7 – Group Track logs Map

As said before, the settings for the track log in the GPS units were not changed before going to the field. This is very clear when comparing the three tracks in the group map. There’s much more points in Kent’s track log, making it even look like a line, while the other two track logs have a smaller amount of points collected. This is part of the settings for the track log, you can set the time interval for the data collection: the lower the time interval, the more points you will get. It’s necessary to find the balance between having a good amount of data, but without compromising the file storage in the GPS.

For last, a map covering the tracks taken by all the students in this class (Figure 8) can give a general idea of the activity. There were six groups divided in three courses, odd number groups would go to the points in ascending order, while even number groups would do it in descending order. Groups 1-2 were supposed to be in the course two, groups 3-4 in the course three and groups 5-6 in the course one. More or less, all the groups were able to navigate over the corresponding courses and the paths taken were similar. Thus, it’s possible to affirm that the groups had kind of the same idea and completed the task successfully.

Figure 8 – Class track logs map.

Conclusion

The activity for this week proceeded much smoother than in the week before. The points were easier to be found, the navigation itself took less than two hours and all the points were covered. However, that doesn’t necessarily mean that the GPS navigation is better than with the map and compass. Specifically for this group, because mistakes were made, the navigation with map and compass was complicated. However, if the appropriate steps were taken, trusting in the compass, a different scenario would be in comparison.

Still, the step count and the need to stop every once in a while to maintain the compass direction delay the process; while with the GPS, the path is automatically corrected in case it goes out of the direction. Then, in this matter, there’s no doubt that the GPS navigation is more effective than with the map and compass.

In the other hand, the precision can be an issue when dealing with the GPS. As mentioned, when the unit is standing in the same place, the accuracy is compromised. It was essential to have three units per group: sometimes a single unit had a high error, putting in doubt if the flag found belonged to the appropriate course. In these occasions, to check other GPS units was useful to guarantee the right placement. The problem with the GPS lack of accuracy is that it’s not possible to know which element has a problem: direction or distance. By using the compass and pace count, the analysis of which one might be dubious.

However, these errors didn’t compromise the navigation, which happened very well, even being in a dense vegetated area – where the PDOP tend to increase. Therefore, it’s not a surprise that the traditional mode was taken over by the technology of the GPS. Especially when dealing with areas not affected so much by multipath effects and other types of errors, there’s no doubt that the GPS navigation is more effective and appropriate for the fast paced routine most of companies and governments have. It doesn’t mean, though, that the traditional technique should be neglected. Although it’s not the preferable way to acquire data or navigate, it should always be known by the geography professionals, so they know how to deal with their tasks if the technologies fail on them.

Navigation Part II - Map and Compass

Introduction

The last report covered the map making and preparation for the following week activity. Then, this report refers to the navigation activity itself occurred at the Priory on last Monday, March 4^th. As said before, this is one piece of a bigger exercise that consists in analyzing different ways to navigate. For this week, the method of navigation was the use of a compass and a reference map. In the following weeks, the navigation with a GPS unit will be covered. The map used for this activity is the one produced in the last exercise by the group, along with the compass; the space count will also be used.

Methodology

The activity consisted in navigating over different levels of elevation, inside the woods, during the formation of a snowstorm. Thus, appropriate preparation was necessary. The first step was to dress properly to go to the field.

One important feature that was not included in the maps yet was the course points where each group would need to go to. The feature class for these points was not available on purpose, so the class could practice the technique of plotting points in a map. Then, a table with different UTM coordinates for each point was given to the students, who started to plot the points in the map (Figure 1). For that, the closest coordinate needs to be found in the grid. Then, considering the distance between grid labels, the point should be apart from the label at the necessary amount, which is an approximation.

Figure 1 - Use of table of coordinates to plot point in the map.

After having the points correctly plotted, it’s created a line between them to represent the path the group should follow. To keep track of this path, it’s necessary to have a known direction. For that, the compass was used to calculate the azimuth from/to each point. The first step to acquire the azimuth value is to correct the compass with the magnetic declination. Because Eau Claire has a declination close to zero, this procedure wasn't necessary in this case. Then, the travel-arrow in the compass is placed in parallel with the path. Holding the compass firmely, to avoid any movement, its housing is turned to be in parallel with the map north. (Figure 2) This is not extremely exact since you can only guarantee the precision by eye. One tactic is to use the lines inside the compass to compare to the grid lines.

Figure 2 - Calculating azimuth with the compass.

Having the values, a table with initial point, end point, azimuth and distance was created to keep organization of each path. However, only the first three fields were completed before the exercise. Instead of using the estimated distance each path would take – which could be done by having a ruler and calculating each path accordingly with the map scale – the amount of steps would be written there after the group walked each path.

In the field, to find the correct direction, it's necessary to turn the compass housing until the wanted value, and then turn yourself until the compass needle overlay with the compass housing "north". Then, the division of tasks within the group would help to increase the efficiency. I was responsible for holding the compass and guaranteeing the right direction by targeting a second person – Kent - who would go as far as he could and then adjust his position accordingly with my compass view. This model was chosen since the trees were almost indistinguishable one from another, so it would be hard to use it as a reference. After having the right direction using these two people, the third group mate – Joel – would walk counting steps to keep track of the distance already walked. When both arrive at the reference – Kent – the procedure starts all over again. Until by approximate calculations, it’s known that the course point was close. Following these procedures, it would be possible to find the necessary points.

Discussion

Some issues related with the precision of the measurements need some attention: in the plotting procedure as well as in the azimuth taking. In the first issue, as it was said, it's extremely rare that points would fall exactly in the intersection of the grid lines. Then, it's necessary to rely on approximations. At this moment, the interval of grid lines shows its importance. Of course that a low interval can clutter the map, but a big interval also compromise the precision in this task: the closer the grid lines are, the more precision you will have. Considering that, the choice of the group of dealing with 20 meters intervals can be considered consistent.

It's possible, even with large intervals, to have a high precision plotting. After calculating the relation between the coordinate labels and the coordinate you need to find, using a ruler, you would plot in the exact place it should be. However, this procedure is time demanding and such precision was not totally necessary with a 20 meter interval.

The precision is subject to the matter also when calculating the azimuth. Since there's a ruler in the compass, it's possible to place it exactly in the parallel with the path. However, the positioning of north can only be measured by the eye. As said before, the existence of north-south lines inside the compass were useful to be compared with the grid lines, which increased the precision of the measurement. Although it's still not completely accurate, the error shouldn't be larger than 5 degrees, what doesn't compromise the navigation in small distances as the ones this exercise deals with. It can be a huge problem, though, when dealing with enormous distances, as in some centuries ago with the marine development.

There's also another problem that didn't compromise the navigation only because the distances were small. The professor advised that, although he asked for an UTM grid, the correct way to navigate with a compass is using the Geographic Coordinate System (GCS). The reason for that is that UTM doesn't have a true north, since all the lines are equally apart from each other. In the real-world scenario, the closer to the poles, the closer the lines would be from each other. That's the way GCS grid lines would be (Figure 3).

Figure 3 - In the top a UTM grid for the United States; in the bottom, a GCS grid. The second has a curvature representing the true north of the map, while UTM doesn't.

It's necessary to have that because the compass relies on a true north, that is the one being showed by the needle. If your north is distorted by the map, that can compromise the accuracy of the measurements. Thankfully, since the area of interest is small, the curvature of the grid lines wouldn't be too high, so this specific navigation was not compromised.

Another matter that could have been improved is the organization of the table made after the point plotting and azimuth taking. As said before, three fields were completed, but the fourth that would have the distance was used as a reference to keep notes of how many steps the group gave.

It would be interesting if instead of having the distance after walking through it, the group had the calculated distance from the line. Using the scale, it would be possible to have it in meters, and then, using the pace count of Joel,  this could be converted to steps. Then, it would be easier to know how far the group were to the target point. Unfortunately, a ruler was not available at the time and the time was short to do this.

Another concern with the distance is that the pace count was obtained in a flat surface without snow. A totally different surface was faced in the field: steeps with about 30 cm of snow. The pace differs in this case, being usually smaller than in a regular surface. That means that the groups should walk more steps than the amount calculated.

Also in the subject of the adverse conditions, it was possible to notice that more preparation need to be made to go back to the field. It was challenging to walk over the deep snow in the steeps, and since the exercise was inside the woods, the dense presence of branches was constant and frequently impacted the pathway of the group. (Figure 4) Rarely it was possible to follow a straight line, so a lot of times, it was necessary to contour any obstacle and go back to the right direction.

Figure 4 - Impact of natural issues on the navigation.

Following all the procedures mentioned until now, it was possible to get from the initial point to the second point, even though the group location was a little east misplaced. This fact brought the idea that some error might have been done in the direction.

In the field, the group discussed about the reasons for that, and it was thought that it was necessary to target the azimuth in longer distances. The reason for that is that if a small error is done in a first measurement when targeting  it's carried on in all the next ones. Then, the less stops the group would made, the less error it would have.

With that in mind, the same procedure was made to find the second point. After walking the necessary distance, the group faced a deep ravine. Then, the map started to be analyzed to support the identification of the area. Unfortunately, a misinterpretation was made: by examining the contour lines, it looked like the point would be in the top of the ravine. (Figure 5) Then, one kept at the correct point, given by the compass, and the others would go look around to see if they would find the point. A long time passed doing that until Martin Goettl - one of the instructors - came and showed that the point was not on the top of the ravine, but on its bottom. 

Figure 5 - Location of point 3 on the contour lines.

After analyzing better the contour lines, it was possible to notice that this was correct and could have been avoided. Two lessons were learned with that: do not doubt your compass - errors might be made, but they would not put you that far of track, as long as you keep careful with it. And also to analyze more carefully the information in the map, it doesn't help to have a very detailed map if the reader doesn't take the necessary time to interpret it.

At this point, it was already more than 5:00 PM, so Martin decided to take the group to the next point while still wasn't dark, and then go back to avoid the darkness.

Conclusion

The main learning obtained in this exercise was about the compass reliability. It was disappointing not to accomplish the goal of the project, however, it was important to make this mistake and recognize it. That way, it's guaranteed that the idea behind the error is understood and it won't be committed again. The idea of misplacement by user lack of precision is right, however, it wouldn't cause big consequences, so it's always essential to trust the compass and don't doubt that much the location you'll be placed.

The contour lines were part of the map to support the area identification, and they would be really useful if the correct analysis was made. Another lesson comes with that: only put information in a map if the reader is able to understand and interpret it correctly, otherwise it can be more confusing than helpful. In the case of this project, the users were knowledgeable about the interpretation of contour lines, and the problem was that it was necessary to be more careful in the reading. However, it's important to understand this relativity of information provided in a map, depending on the target audience. If something is supposed to be released for the public, it might not be a good idea to insert technical concepts and features.

For last, it's important to recognize the positive sides of using a compass and map: even inside the woods, the precision is not compromised. Sometimes, when inside a really dense forest, a GPS unit can have an error too high or even not acquire satellites enough to display the coordinates. However, technology keeps developing more and more to avoid these problems. The downside is that to navigate with compass and a map is a very time demanding technique. Nowadays, the world requires efficiency at a high rate, so more practical solutions replace this method.