Collecting and Using GCPs with PIX4Dcatch and the Emlid Scanning Kit

This article will demonstrate how to collect and use ground control points in the PIX4Dcatch app as well as best practices for scanning the face of a building using the PIX4D + Emlid Scanning kit. 

In this article I will demonstrate how to use the survey function in Pix4Dcatch to incorporate ground control points in your Pix4D scanning kit scans. We will start in the Survey tab by tapping New Collection, naming our survey file, and setting our coordinate system. With our survey project created we can start marking our targets. Note that if you process your scans in Pix4Dcloud you’ll need to collect your GCPs before you scan, as seen here. With our RX on a survey rod we will plumb our rod over our GCP and tap New Point. From this screen we can name the point, set our rover rod height, add a description and reference photos if desired, and finally, set our averaging time for the point collection. Tap Measure and after we finish averaging, we will have coordinates for our first GCP. We can then repeat the process for the rest of our GCPs.  

Once we have all our coordinates collected, we can get ready to scan. We will tap on Capture, then the Tools menu in the bottom right corner. Tap Tag Detection and Import Point Collection, then select our recent survey project which will enable auto-tags as well. We can then install our RX back on our scanning kit handle along with our phone. Since I am trying to capture this facade of the building, I’m also going to install my survey rod into the bottom of the handle so I can get a good capture of the whole face. For best results I will make one low pass and one high pass keeping a steady pace and consistent distance from the building face. I’ll also make sure to recognize both GCPs in the scan so I can tie this scan to them as well as the scan from my aerial drone collection for accurate merging.  

With our scan complete we can now export it to Pix4Dmatic or upload it to cloud for processing.