Aerial Mapping With UAS I and II

Introduction

Aerial imagery can be processed and used in many different ways for many different reasons. The broader view and different vantage points of aerial imagery are huge benefits for many different reasons. Equipment that utilizes aerial imagery can be in the form of a balloon, kite, UAS, or rocket. The class used to of the former ways, the UAS and balloon, to view and process aerial imagery. Many preparations go into aerial imagery including using cameras, GPSs and other technical equipment. The class got to go outside and test the equipment at the Eau Claire Soccer Fields. This blog is two-fold. The first part is focused on image taking, processing, and the mosaic method. While the second half is a UAS mission pre-planning and flight.

Study Area

The Eau Claire Soccer Fields are located approximately 1 mile south of UW-EC campus. The fields are a large open area near residential housing and the Eau Claire Indoor Sports Center. The openness of this area allows for great flying. The area was suitable for the balloon because it had a great range of motion and could fly very high (500 ft). This ability to fly high allowed for a larger area to be captured. For the UAS the openness of the area allowed for easy maneuvering and easily accessible control points.  

Methods

The balloon was a simple large rubber helium balloon attached to a string with a picavet rig. The picavet rig is attached to the string and is where the camera and GPS are attached. Two cameras were attached to the picavet rig, these were a Canon Sx260 and a Canon Elf. The reason for 2 cameras is to get as many shots as possible and see the difference that multiple mediums take in the same area. The GPS was attached to know where the location was for the future process of mosaicing. Once all the equipment was set up the balloon was then lifted into the air at preplanned height of 500 feet. The class then walked around the field to capture multiple images. The route that the class walked was made to utilize the largest area so that many images could be captured. The route was made for minimal overlap, but some overlap is good. Hundreds of images were collected for mosaicing.

After the fieldwork was all done image mosaicing had to take place. Image mosaicing is basically stitching images together to make one large image. This is where hundreds of images come in handy as well as overlapping of images.

Figure 1: The balloon before take off. This shows a size reference for the balloon.

Figure 2: The two cameras and the GPS mounted on the picavet rig

Figure 3: The balloon ascending into the air

PhotoScan

To create mosaiced images in Photoscan add the photos you want under the Workflow tab. After adding the photos go back to Workflow and select Align Photos. This alignment of photos creates Point Cloud which are points of the photos. After the alignment select Build Mesh from Workflow. The mesh will create a TIN which is a Triangular Integrated Network. This means that triangles are created from points to create pieces of an image. In tabs click Texture. To export the image to use in other program click Export Orthophoto. The best option is to save it as a TIFF. After the TIFF is saved and exported open ArcMap. This step is needed only if the image is not geotagged. To geotag the image open Geoprocessing. Open an image of Eau Claire that has been geotagged. Click Viewer which is the magnifying glass this opens a spate view with the area that is not georeferenced. Adding control points to the image will help geotag. To get the track log another software program is used. This is Geosetter. Geosetter will help create GPS points and rectify the image.

Figure 4: An image mosaiced together in Photoscan. As one can see the area is quite large

Figure 5: Another mosaiced image from Photoscan

UAS Methods

There are many pre-planning methods that go into UAS use. If any step is missed the whole operation could be a mess. Tests should be ran before the UAS start up.  This includes waiting for a GPS connection and a connection between the UAS and software that is used to fly. The software the Professor Joe Hupy uses is Mission Planner. Mission Planner is freeware that can be used by anyone. Connection to Mission Planner from the UAS is signified by a green light on the software. No less than 3 people should run a UAS mission. The 3 members ideally should be a pilot who manually controls the UAS, a pilot at the computer, and an engineer that knows all the software. One should first know the topography of the land before flying as to best map out a flight plan.

Figure 6: Professor Hupy using the Mission Planner software prior to UAS launch

For Mission Planner there is a grid of points. These points are referred to as waypoints and are number in sequence. The first point is home and the UAS will return home when it has hit all the points. If the UAS is at 60% and is not close to home the pilot should force the UAS to go home. Once the UAS lands the pilot disarms the UAS and makes sure that everything is off. Professor Hupy’s Y6 rotocopter has a flight time of roughly 15-20 minutes. The area that was chosen had a flight plan less than that so no issues arose.

Figure 7: Professor Hupy's Y6 rotocopter prior to flight. Next to the copter is the controller

Discussion

UAS and other alternative aerial imagery processes have many positives and UAS definitely looks to be the future of aerial imagery and remote sensing. With UAS the cost is cut down and the areas acan be explored more broadly. The alternative of UAS is a booming industry and can be used for anything from police work to agriculture.

Conclusion

UAS removes the human element and allows for a more expansive area of work. The camera does not have to be that advanced on any form of aerial imagery but to think of the future of camera resolution it is amazing. UAS work is more expansive than the current alternatives of balloons, kites, and rockets. The future is very bright with these advancements.