UAV Flight with GCPs Covering the Eau Claire South Middle School Community Garden

Introduction:

On May 2nd, 2017, at 3pm, class visited Eau Claire's South Middle School Garden to fly the DJI Phantom 3 and DJI Inspire and capture NADIR and oblique imagery, and collect GCPs with a 2 cm accurate GPS to aid with spatial accuracy in later processing. This experience aimed to give experience in the field with what comprises a UAS flight, and was less focused on the processing aspects which have already been covered and can be seen in the past posts below.

Methods:

Nine GCPs were laid out in the garden on a three by three grid, making sure that the outermost GCPs were close to the fence, and that the grid covered sufficiently the entire garden. The GCPs had numbers painted on them for identification in the images later, but were laid out in a snaking pattern up and down the garden grid the pattern of which was noted in case the numbers were not able to be seen in the imagery for any reason. The locations of each numbered GCP were important because each GCP corresponded to a same numbered point that was recorded on the survey grade GPS unit.

Figure 1: GCP Collection

Figure 2: Screen of the GPS Unit Showing Horizontal and Vertical Precision

When collecting the GPS points with the unit is was of vital importance to make sure the unit was completely vertical using the leveling bubble on the shaft of the unit. This ensured the coordinates at the top of the unit (where communication with satellites was from) were the same as the coordinates at the point at the bottom of the shaft where the shaft met the center of the GCP board. It was also of vital importance that the GPS unit was set up to be using the UTM coordiate system. Points were taken in the same snaking pattern as the GCP boards so that the numbers on the boards corresponded with the numbers of the points being taken.

Figure 3: GPS Leveling

After getting the GCPs taken, the class could move on to UAS flight. As the location had been used before for testing, it was known that there was LTE signal, and that the Verizon MiFi device would successfully be able to supply WiFi. Because of this, flight planning was left for the field as base map data could be pulled down in the field. If it was unclear that there would be signal, basemaps would have been cached in advance onto the control tablet int he control software.

Figure 4: The DJI Phantom 3 Advanced

This availability of internet connection was also vital when it was found that the DJI done would need to update its firmware. Firmware updates on DJI drones are not optional, and drones will not fly unless the newest updates have been done.

Figure 5: South Middle School Community Garden

After the updates, the Phantom was flown. The drone was planned there in the field to make a snaking pattern covering of the polygon created in the software covering the garden using an elevation of 70 m AGL (above ground level). The takeoff and landing points were made to be the same, and the rally point was also that same point. Rotors and other pieces of the aircraft were then attatched. The takeoff was then made manually as is always done. After takeoff, and rising to an appropriate elevation to play around with controls, turns were made in all directions and all other functionality was tested to make sure that the automated mission would be a success. Then, the drone was raised to the elevation that the mission would be conducted at before starting the mission, as is good practice so that the drone would not hit anything at lower altitudes en-route to the start of the mission. When the drone returned to its starting position and began to beep, letting the PIC (pilot in control) that the mission was over, the PIC gave the drone the command to begin automated descent and landing.

The result if the phantom flight is shown below. The markings are of the nine GCPs.

Figure 6: Overview of NADIR Phantom Flight with GCPs

The Phantom also flew another flight using the same procedures. This flight was planned to capture oblique imagery along the road, however. The three dimensional model created from that data, processed in Pix4D just like the NADIR imagery except with the three dimensional model template option selected, is shown in the below figures. This flight flew a corridor along the road, and therefore covers far less area. The area it does cover however is more accurate. This can be seen when contrasting the sides of the cars that face away from the garden on the opposite side of the road as the garden in the NADIR and the oblique data models.

Figure 7: Oblique 3D Model

Figure 8: Alternate View of Oblique 3D Model