UAS III - Balloon Mapping

Introduction

     Unmanned aerial systems (UAS) can take on many different forms.  In previous labs we learned how basic UAS units work and the different ways to attach a GPS and a camera.  On Monday, April 21, 2014 the Geog 336 class returned to the Eau Claire Indoor Sports Center grounds (Figure One).  The plan was to get really good imagery of the entire property and a little outside of it.  This required group thinking in how we would make sure to cover the whole are and get enough overlap to make sure not spots were skipped over.

Figure One - At the center of this map is the Eau Claire Indoor Sports Center grounds.

Methods

Balloon March

     A large weather balloon was used as our UAS for the day.  In order to fly the balloon, it needed to be filled up with helium.  When properly filled up, the balloon was about three feet in diameter (Figure Two).

Figure Two - Cody is holding on to the balloon to that it does not fly away before we are ready.

After completely filled, a hardy piece of rope on a spool was attached to the balloon so we could have control over it.  An additional string attached to the rope holds the GPS and the camera (Figure Three). 

Figure Three - Joe Hupy has just attached a simple camera and GPS to the balloon rope by a string.  The weight of the devices should be enough to keep the camera point downward.

The camera was set to take a photo every five seconds.  About four students traded off having control of the balloon while the camera was snapping photos.  

PhotoScan

Click Workflow on the Tab list.  Click Add Photos.  Only add the photos that are necessary.  If many (over 200) pictures are used, the program will take hours to complete the process.

When the photos are added, return to the Workflow tab and click Align Photos.  This will create a point cloud.  Click Build Mesh to create a Triangulated Irregular Network (TIN) from the point cloud.

Next, click on Create The Texture under the Workflow tab.  This needs to be turned on in order to see a difference in your images.  Look for the Texture icon under Tabs to do this.  Cameraicon can be clicked to turn off the blue squares.

To able to use the image in other programs, it needs to exported as a .jpg, .tiff, or a .png file format (Export Orthophoto).  A .tiff files may be best.  This file can now be brought into ArcMap.  It would also be a good idea to add imagery as a basemap.

Open the Geoprocessing Tool-set in ArcMap and click on the Viewer icon (button with magnifying glass).  The .tiff file will open in a separate viewer.

Control points need to be added to the photo shows up where it is supposed to be spatially (Add Control Points).  Once this option is clicked, select a point on the orthophoto, then click on corresponding location on the satellite image.  Get a widely dispersed set of control points to pin down the orthophoto against the ArcMap basemap.  At least 10 control points should be used to ensure that the photo is not skewed, stretched, or otherwise distorted in any way.  Once this is done, click Rectify in the Georeferencing toolbar.

Geosetter 

In Geosetter, the images that you want to use need to be selected.  They will go into a separate viewer box.  Make sure none of the photos have blue markers on them, this mean coordinates are attached to them.  

Click on the icon labeled "2" in Figure Four.  This makes the tracklog embed and select-able into the images.

Click Synchronize with Data File in the new window that opens up.  Input the GSX track log (Figure Five).

Figure Four - The GeoSetter interface.

Figure Five - Embedding the tracklog by time into the images.

To save images, close the program and click "yes" when the prompt asks you to save.  The coordinates will also be saved to the images.

Results

Figure Six - This image shows the amount of overlap of the images used in the mosaicking process.

Figure Seven - This is the result of the mosaicked images.  The orientation is not corrected because it has not been georeferenced yet at this stage.

Figure Eight - This is the result of the images from the other camera.  This camera took images that were a little darker, which can easily be corrected, but this is the raw data.

Figure Nine - This is a DEM of the mosaicked georeferenced orthophoto.  

Conclusion

     Using a balloon for a UAS was found to actually work pretty well.  Even with a cheaper digital camera and GPS, mapping from imagery can still be done.  The combination of these collection methods along with PhotoScan and GeoSetter can make a fairly accurate map even on a budget.  Planning is still an essential part of flying this kind of UAS.  If the weather would have been poor that day, the balloon may have not been the best choice for a UAS.  Luckily, the day our class went mapping was relatively sunny and the wind was not too bad.  If time was an issue, the balloon may not be the best choice either.  Walking with a balloon on a rope can be time consuming, especially if the area of interest is larger.  For the purposes of this exercise, the balloon mapping worked very well.