Lab 6 GCP's in Pix4D

Introduction

• In this blog we look at how we took Pix4D and how we made an orthomosaic with GCP's. Ground control points or GCPs are marking on the ground made by the surveyor to give him/her exact locations to go off when making the ortho. This allows the ortho to be created with less errors, because as the images are overlapped you know the exact location of the GCPs and can use them to make sure the images are stitched together correctly. 

Processing

• First off the data i wanted was added to the computers C drive. Next I opened up Pix4D and added a new project and check the XYZ coordinate system which needs to be YXZ in order to correctly work.
• I next checked all the images that i wanted to use and selected rolling shutter. then selected to only do Initial processing Figure 1 shows us the initial processing taking place. 

Figure 1

• The metadata for the flight is Date Flown: June 13th, 2017

• UAS Platform: M600 Pro
• Sensor: Zenmuse X5
• Altitude Flown: 70m
• Ground Control GPS: Trimble UX5
• Ground Control Coordinates: WGS84 UTM Zone 16
• UAS Coordinates: WGS 84 DD
• Pilot: Peter Menet

• After the processing was done we had a point cloud Figure 2, and a PDF report with the processing and data analysis 

Figure 2

• The next step was to correct the GCP's in figure 2 they were already corrected but when first done the points were floating in space with no correct position. To do this i went to each data set and browsed around until i found the correct marking in the picture. Most were pretty distant. it normally took marking the point on 2 images before the computer was able to identify the correct point. After this was done the GCP's  showed their position on the ground as correctly placed.

• After all this was done I could now finish the processing. This took around an hour similar to the previous lab. Once  the processing was done we got figure 3 which shows all the corrections it made from before. At point you can see it corrected the altitude from which the photos were taken and bought the GCPs down to an accurate position

Figure 3

•  Then I selected triangle to mesh the points together to create a nicer looking image as seen in figure 3 and figure 5.  After all the processing is done we moved the data out of the C drive.  As seen in the images the ortho is neatly stitched together and shows pretty accurately a picture of the area.  The processing had given us useful information which i then open ArcMap.

figure 4

Figure 5

• Figure 6 is the complete image of the mapping which i used information derived from the proccessing in Pix4D and added it to ArcMap. From that I added the main ortho with a scale bar and direction indicator. Then added title watermaker and metadata. After the easy stuff was done i added in a indicator map which marks the site on a zoomed out map, a DSM to give us heights and finally topographic image.  

Figure 6