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Including GCPs in image processing
Including GCPs in image processing

Add ground control points to increase your the accuracy and precision of your drone mapping products

Karen Joyce avatar
Written by Karen Joyce
Updated over a week ago

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

  1. 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.

  2. Survey in your GCPs, preferably using a differential GPS (dGPS).

  3. You may also opt to use a PPK system to correct your data.

  4. 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.

  1. Upload your GCP csv file from the previous step into the GeoNadir GCP matching site.

    1. Your .csv must contain 4 columns (as above)

    2. The first row must be the header and contain GCP Label, Y, X, Z

    3. Each subsequent row contains the label and coordinates of your ground control points (in the selected coordinate system units specified by the EPSG code)

    4. No cells can be left blank

    5. GCP labels must be unique

  2. Specify the coordinate reference system of your CSV using an EPSG code or a PROJ string

  3. 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.

  4. Download the gcp_list.txt file - it should look something like the image below

Uploading matched GCPs to GeoNadir for processing

  1. Add a single dataset to GeoNadir for uploading

  2. In the upload dialog box, scroll down to the point where you can add your matched GCP file

  3. Browse for or drag and drop your matched GCP file

  4. Add other metadata as required

  5. Click to upload as usual

  6. If you have other datasets to upload, you can continue to do so while these data are being processed.

See the video below for a complete example of the workflow

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