Balloon Mapping & Mosaicing

INTRODUCTION

Our Geospatial Field Methods class constructed then launched a balloon mapping rig to collect aerial imagery of the University of Wisconsin Eau Claire campus.  The imagery was then georeferenced and mosaiced to  be used as an aerial map.

The class constructed the balloon apparatus prior out of a styrofoam cooler and  an empty soda bottle. A digital camera, tracking device and GPS were attached to the rig as well as a large weather balloon filled with helium.  A string was connected to the weather balloon and used to control the device

METHODS

The construction of the balloon mapping apparatus required careful preparation.  We had to measure each and every item used in the device so we knew how much the balloon mapping device would weigh.  

Figure 1- Students weighing each item used to
construct the balloon mapping device

Students tested and timed the parachute, constructed rigs for the balloon applications, determined the best camera for the launch and designed the implementation of the continuous shot (Figure 3) and tested the tracking device.

Figure 2- Implementing Continuous
Shot

Once the balloon mapping device was constructed, we filled the weather balloon with helium and measured the string to 400 meters.  We attached the string and balloon to the mapping device.  The next step was to launch the balloon mapping device.  This was done by unravelling the string until all 400 meters were unraveled.  Two students held the string connected to the balloon mapping device and walked around campus to collect aerial imagery of the area.  When we believed a sufficient amount of footage was captured and a sufficient sized area was covered the string was taken in so the mapping device was grounded.  The images were uploaded to a computer to be mosaiced together.

Two techniques were used to mosaic the aerial imagery; a website called mapknitter and georeferencing through ArcMap.

Mapknitter is a website that provides tools necessary to "knit" together aerial images to create a map.  A Google Imagery base layer was offered by the website.  This base layer could be used as a reference for the placement and scale of the imported images.  Once an image was uploaded it could be scaled and moved so it could be located in the correct position.  This was done repeatedly with numerous images until the images were sufficiently placed.

Figure 3: Aerial Imagery map created with MapKnitter (mapknitter.org)

The second technique was georeferencing with ArcMap.  Because there was such a large amount of images to be mosaiced, the class was divided into groups.  Each group created a mosaic of images of a certain area of campus.  Data was uploaded to a map document that would be beneficial to the process of georeferencing.  The data included a polygon feature class for my groups section and a CAD polygon feature class of the buildings on campus (Figure 4).  I used an imagery basemap provided by ESRI in the beginning of the process as a reference.

Figure 4- Group Section & Buildings feature classes

After this data was added the images were georeferenced to create a mosaic raster data layer.  Below are the steps necessary for georeferencing.

1.) Turn on the georeferencing toolbox

2.) Click the "Control Points Tool"

3.) Zoom to the current image

4.) Click a point on the current image that can be easily referenced to the buildings feature class

5.) Zoom to the Group Section layer

4.) Click on the area that matches the point previously selected on the current image

The image will move to a new location using the georeferenced point; do this repeatedly for each image until the image is placed in the correct area.  This process is repeated for each image until an area is accurately represented on the map.

The design of the mapping devices were improved upon and then implemented into the launches.  The class launched the balloon mapping apparatus multiple times so the improved devices could be used.

Figure 5: Final mosaiced raster dataset of the aerial images for section 4

Discussion
This was the first experience with balloon mapping for the students and professors in this class.  Trial, Error and Editing was crucial to the process.  The class analyzed each step of the process and fixed the problems that arose; doing so helped the class to find the best way to collect aerial imagery.  A fin was attached to the balloon mapping apparatus.  In my opinion the fin improved the device the most.  It helped manage the wind, so the images were collected at more uniform angles.

The first launch resulted in somewhat disastrous results.  Students took the device over the Chippewa River on a very windy day, the string snapped and the weather balloon was lost.  Luckily, the camera and tracking device were placed in a floatable box, so we were able to retrieve those objects.  The next time the balloon mapping device was launched the students reeled in the string while crossing the river so there was less tension on the string.

ArcMap 10.1 produced a better result and it was easier to georeference the images in this technique.  It was also a good resource to use because you could go back and edit the control points.  This wasn't available in Mapknitter, so if a project was greatly distorted you had to delete the image and start over.

The images taken from the balloon are not at a constant altitude or angle.  This makes it hard to match the images perfectly and some of the areas are distorted because of this.  To avoid this problem as much as possible, the images overlapped each other in many areas.  This problem can be seen in the area of the walking bridge and Schofield Hall in the final map.

Aerial Imagery Mosaicing

Introduction
Our class has created and implemented a balloon mapping rig in the previous weeks.  This is an innovative and cost-effective way to collect aerial imagery.  In order to use the aerial imagery, the images collected by the balloon must be georeferenced and mosaiced.  This report concentrates on the process of both mosaicing and georeferencing images from our balloon mapping.

Methods
Two techniques were used to mosaic the aerial imagery.  For both techniques the images were uploaded to a desktop after the balloon was grounded.  The techniques used were very different; the first technique was using a website called mapknitter, the second technique was georeferencing through ArcMap.

Mapknitter is a website that provides tools necessary to "knit" together aerial images to create a map.  A Google Imagery base layer was offered by the website.  This base layer could be used as a reference for the placement and scale of the imported images.  The images had to be uploaded to the site one at a time.  Once an image was uploaded it could be scaled and moved so it could be located in the correct position.  This was done repeatedly with numerous images until the images were sufficiently placed.  Once this was complete, the map had to be exported so it was visible to all users of the mapknitter site. The map I created on mapknitter is seen in Figure 1.

Figure 1: Aerial Imagery map created with MapKnitter (mapknitter.org)

The second technique was georeferencing with ArcMap.  Because there was such a plethora of images collected by the balloon, the class divided sections of the campus into groups to lighten the workload for all students.

I started a new map document then loaded data that would be beneficial to the process of georeferencing.  The data included a polygon feature class for my groups section and a CAD polygon feature class of the buildings on campus (Figure 2).  I used an imagery basemap provided by ESRI in the beginning of the process as a reference.

Figure 2- Group Section & Buildings feature classes

After this data was added the process of georeferencing could begin.  This process if not very complicated, but it is time consuming and must be done carefully.  Below are the steps necessary for georeferencing.

1.) Turn on the georeferencing toolbox (Figure 3)

Figure 4: ArcGIS Desktop 10.1 Georeferencing toolbar

2.) Click the "Control Points Tool"

3.) Zoom to the current image

4.) Click a point on the current image that can be easily referenced to the buildings feature class

5.) Zoom to the Group Section layer

4.) Click on the area that matches the point previously selected on the current image

The image will move to a new location using the georeferenced point; do this repeatedly for each image until the image is placed in the correct area.  This process is repeated for each image until an area is accurately represented on the map.

Zooming between layers is helpful because the aerial imagery is not spatially referenced and is located very far from the needed area.

The georeference control points can be edited using the "Control Points Table" (Figure 5).  The control points are labeled by a number and when clicked on, the control point will be highlighted on the map.  Editing mainly consists of deleting control points if it distorts the image or the image's location on the map.

Figure 5: Control Points Table

Results

Figure 6: Final mosaiced raster of the aerial images

Discussion

Although I was apprehensive to use ArcMap to mosaic the aerial imagery together, I believe ArcMap 10.1 produced a better result and it was easier to georeference the images in this technique.  It was also a good resource to use because you could go back and edit the control points.  This wasn't available in Mapknitter, so if a project was greatly distorted you had to delete the image and start over.

The images taken from the balloon are not at a constant altitude or angle.  This makes it hard to match the images perfectly and some of the areas are distorted because of this.  To avoid this problem as much as possible, the images overlapped each other in many areas.  This problem can be seen in the area of the walking bridge and Schofield Hall in the final map.

Field Navigation IV

INTRODUCTION
Navigation in the field is incredibly important in field methods.  Accuracy in the field is dependent on the type of navigational resources available and can be skewed with the simplest miscalculation.  In the previous weeks, our class used different type of navigational resources to navigate through a newly acquired property for UW-Eau Claire, The Priory.  Maps, compasses and GPS units were used as navigational resources.  Students were put into groups of three and given a specific course to navigate.  Each group had to find waypoints in order to finish their course.  When the GPS units were used groups plotted points at the waypoints and a tracklog was used to note the course.  After we navigated the course in the field we used ArcGIS to import the GPS data and to create maps of our routes.

Each activity built on our knowledge of field collection.  The activities also introduced the students to other ways of navigating.  It was important for us to experience working in the field because we learned to overcome challenges that were presented by the weather, terrain and technology.

2.)This week we used the navigation maps from the previous exercise and applied our pace count to find waypoints at The Priory.  This straightforward exercise presented challenges due to the weather, terrain and lack of navigation technology.

3.) This week, we expanded on the navigation exercises of the previous weeks.  A GPS unit was used to navigate to waypoints without the use of a map or compass.  Students were provided a list of Lat/Long points by the professor for each waypoint.  Students activated the tracklog feature of the GPS unit in order to track their route throughout the activity.

4.)You have the class period to complete all 15 points from all three courses. The first group finished wins.  Make sure you use the punch on your cards at each flagged location.

METHODS

For the first weeks exercise only a map and compass were used to navigate The Priory.  Each student had to calculate their pace count before going in the field.  A pace count takes into account how many steps a person takes within a given distance.  This information allows a person to know how far they have traveled without the use of a GPS unit.  The distance for our pace count was 100 meters.  To determine my pace count, I walked at a normal pace counting every pace (every other step) for a pre-measured distance of 100 meters.  I repeated this process three times and took the average of the count-70 paces.  Knowing my individual pace count helped me to account for the distance I travel while navigating at the priory.

Two navigation maps were created for the first week's exercise.  The first map was an overview of the area (Figure 1), while the second was more precise and include topography (Figure 2).  Our professor supplied data included CAD drawings, aerial imagery and polygon feature classes.  Topographic data was also provided by the USGS.  The data was projected to NAD 1983 UTM Zone 15 North so a UTM grid could be applied to the maps.  A polygon feature class of the boundary was supplied by our professor as well as a point feature class of the waypoint locations.  This data helped us to reference our location in relation to the waypoints.

Figure 1- Overview navigation map

Figure 2- Navigation Map with 2 and 5 foot contours

When we reached The Priory on our first day of navigation,our professor provided a list of X and Y coordinates of the waypoints (Figure 3).  We used these coordinates to plot the points on our navigation map. We then used a compass to note the angle of direction on our map.  This information would be used in the field to better navigate the waypoint courses.  We also measured the distance in meters from one waypoint to the next so we could use our pace count in the field to determine our distance.

Figure 3-X and Y coordinates of waypoints provided by Joseph Hupy

Once in the field, we started at point 1A.  We used our compasses to find the correct angle of direction.  We sent one person out about 150 feet and aligned their position to the necessary angle (Destination).  One person stayed behind to make sure the angle of direction was followed (Angler).  The other person walked while using their pace count to the person who was aligned with the angle of direction (Runner).  We kept track of how many paces it took for the runner to reach the destination so we could determine how much further we had to travel to reach our waypoint.  We broke up the distance between two waypoints so we could send out the destination person to an area where they were still visible to make sure we kept the correct angle of direction.  This process was repeated over and over to navigate through the course.  Once we reached a way points, we punched a course card given to us by our professor with the stamp at each waypoint.

During the second navigation activity students were allowed to use a GPS unit and map to navigate the course.  To begin we had to find the starting point of our route, the location was indicated by the list of lat/long points given to us by our professor.  At the starting point, we activated the tracklogs on the GPS units.  We made sure to activate only when we reached the starting point so only our course was tracked.  From the starting point, we used the lat/long feature of the GPS unit to navigate to the first way point (Figure 4).  We observed the increase and decrease of the lat/longs on the GPS unit to determine which direction to travel.  This was done for all six waypoints on our course.  After we had found each waypoint, we traveled back to the starting point to complete the course.  Upon reaching this point, we turned off the tracklog.

Figure 4-Navigating with the GPS unit

Figure 5- Zac & Phil located a waypoint

Using the DNR Garmin application, students uploaded their individual tracklogs onto a computer.  Through this program, the tracklog could be easily converted into a point shapefile.  The shapefile was then imported into the class geodatabase.  Once the data was imported, three maps were created.  One map showed the tracklogs for every student in the class (Figure 6).  Another map showed the tracklogs for my group (Figure 7) and another for my own tracklog (Figure 7).

Figure 6- Map of the tracklogs for each student in the class

Figure 7- Map of my group's tracklogs

Figure 8- Map of my individual tracklog

For the third activity, we used a GPS unit and map again to navigate to waypoints.  For this activity groups had to navigate to every waypoint, 15 in total.  We were also given paintball guns to add some excitement to the activity.    The same techniques were used as the previous week.  The same three maps were also created for this activity (Figure 9).

Figure 9-Week three maps: Class, Group and Individual Tracklogs

DISCUSSION

These activities taught me how different technologies can be used for navigation.  It is easy to assume the the highest techology is always best, but these activities showed me that it is possible to navigate accurately with simply a map and compass.

I also learned a lot about working together as a group through these activities.  Our group worked together very well, this helped our group to navigate efficiently.  One thing that did not work well for our group was using the pace count.  The pace count was difficult to use  because we measured our individual pace count on a flat surface with no obstacles before this exercise.  We found that our pace counts came up short for each waypoint in the field due to rough terrain and the amount of snow on the ground.

Technology does not always make navigating easier.  Although we were allowed to use a GPS unit to navigate in the last two weeks, it was not easier than the compass and map navigation.  It was somewhat difficult to determine the direction of travel using lat/long the the GPS and a group member had to be constantly watching the lat/long numbers to make sure we didn't stray off of our direction.  Even though it was more difficult to navigate with a GPS unit, it took less time to navigate using this technique.

The transformation from the GPS unit to a GIS shapefile caused the features to be somewhat skewed.  Waypoints did not fall exactly in the correct location and the tracklogs were somewhat inaccurate as well.  This is one deterrence that is unfortunate but can be fixed through editing in ArcGIS.

CONCLUSSION

All of the techniques that we used to navigate were important in their own way.  It is important to know not only how to use these technologies individually, but also how to use the technologies as a combination.  We used techniques that are not technologically advanced (map, compass) and technologies that were advanced (GPS units).  The activities showed the benefits and drawbacks of each technique.