Who can use this feature
Owners and editors with a Pro + subscription
Including ground control points (GCPs) into your processing workflow can increase the positional accuracy of your orthomosaics, DSMs, and DTMs in the x,y, and z dimensions. It is however a multi-step process that can be a little time consuming, but is not complicated.
Capturing GCP data in the field
Make sure that your ground control points will be clearly visible in your drone mapping images. Ideally you have a minimum of five and they are spread out over your entire capture area. Learn more about GCP numbers and distribution here.
Survey in your GCPs, preferably using a differential GPS (dGPS).
You may also opt to use a PPK system to correct your data.
Export your GCP data (y,x,z) to a CSV file. It should look something like that below. It should have ONLY four columns being the GCP point name, Northing, Easting, and height.
Matching GCP data to images
This process can be a little fiddly. It's summarized in the steps below, but we recommend you watch the short video at the end of this section to fully understand the requirements.
Upload your GCP csv file from the previous step into the GeoNadir GCP matching site.
Your .csv must contain 4 columns (as above)
The first row must be the header and contain GCP Label, Y, X, Z
Each subsequent row contains the label and coordinates of your ground control points (in the selected coordinate system units specified by the EPSG code)
No cells can be left blank
GCP labels must be unique
Specify the coordinate reference system of your CSV using an EPSG code or a PROJ string
Tag your GCPs with their location on a minimum of three (preferably five or more) matching photos. Please make sure that there are no spaces in the file names of the photos.
Download the gcp_list.txt file - it should look something like the image below
Uploading matched GCPs to GeoNadir for processing
Add a single dataset to GeoNadir for uploading
In the upload dialog box, scroll down to the point where you can add your matched GCP file
Browse for or drag and drop your matched GCP file
Add other metadata as required
Click to upload as usual
If you have other datasets to upload, you can continue to do so while these data are being processed.
For more about the complexities of GCPs in marine environments, catch up with our blog here.
See the video below for a complete example of the workflow