Community Garden Phantom Flights

Introduction

For this weeks activity, the class met at the Community Garden right behind South Middle School in Eau Claire, WI. Students practiced with setting up the GCPs constructed in the previous week and collecting the coordinates of the GCPs using a survey grade GPS. Students were then introduced to the DJI Phantom Advanced which was then used to map the garden. The imagery along with the GCPs was to then be processed in Pix4D.

Methods

Using the GCPs that were constructed the previous week, students set up GCPs 1-9 around the garden in a well spaced out fashion. The GCP coordinates were then collected using a survey grade GPS unit where the unit was placed directly over the GCP before collecting the point. GCP coordinates were collected in order from 1 through 9, that way the numbers on the GCPs themselves would match up with the GCPs in the Pix4D project when transferred over into Pix4D.

Phantom Flight 1

After the coordinates were collected, the instructor introduced students to the DJI Phantom Advanced and went through certain controls and how to set up a flight before launching the UAV. For this flight, the flight was flown at 70 meters and captured images of the garden that contained the GCPs.

The images were then processed similarly to that of the previous exercise 'Processing Pix4D Imagery Using GCPs.' The instructor provided the images for flight 1 in a separate folders and the GCPs in text file format which could then easily be transferred over into Pix4D.

Step 1: Create a new project in Pix4d. Give it an appropriate name (20170502_gardenphantom_gcps) and save it to a personal folder created for this assignment

Step 2: Add images from folder 20170502_garden_phantom_70m > Flight1

Step 3: Go into the editing options for the camera and change the Shutter Model to 'Linear Rolling Shutter'

Step 4: Select '3D Maps' for the template

Step 5: Go into Project > GCP/MTP Manager and click on 'Import GCPs' and select the file 'GCP20170502_MASSAGED.txt' and change the Coordinates Order to the 'Y, X, Z' option

Step 6: Uncheck processing steps 2 and 3 and click 'Start' to begin Initial Processing



Results/Discussion

Conclusion

Constructing GCPs

Introduction

For this week's activity, the instructor guided students through the process of constructing homemade ground control points (GCPs). As discussed previously, GCPs assist in georeferencing aerial imagery by attaching a coordinate to the GCPs themselves which is critical for the orthorectification of remotely sensed imagery. Creating GCPs by hand can be cost effective and will last a very long time depending on the quality of the material used.

Methods and Results

Figure 1: GCP construction material

The material used for the GCPs was a black, high density polyethylene sheet (8' x 4' x 1/4")(figure 1).

Figure 2: GCP cut down size

Using table saws, the polyethylene sheets were cut down into squares as seen in figure 2. The pieces were then laid down across bed sheets in preparation to be spray painted.

Figure 3: Spray painting triangle side 1

Using a wooden cutout in the shape of a triangle, the cutout was placed on top of the black square. Using neon pink spray paint and firmly pressing the cutout to the black square, the triangle was painted onto one side of the square (figure 3).

Figure 4: Spray painting numbers

While allowing the first triangle to dry, using neon green spray paint, numbers were painted onto what would be the adjacent black triangles on both sides in numerical order (figure 4). Each GCP was numbered "1, 2, 3,..." and so on.

Figure 5: Spray painting triangle side 2

Once the first triangle was dry enough, using the wooden cutout once again, the second pink triangle was painted opposite of the first triangle (figure 5). Once all GCPs were spray painted with triangles and numbers, they were then allowed to completely dry (figure 6).

Figure 6: Final result of GCPs

Conclusion

The GCP construction went smoothly without incident. Approximately 16 GCPs were made within about a 45 minutes time span which was pretty efficient. Initially the triangles were going to be green and the numbers pink, but these were switched at the last minute in hopes that the pink will stand out better in the imagery compared to the green color. These GCPs will be used in a future activity.