Collect ground control points
Set your ground control points using an RTK unit and easily identifiable markers. Check out our detailed instructions here. You can also ask your projects surveyor for the ground control points.
Upload ground control points to Manager
Click the + button in the bottom toolbar and select GCPs. Then drag and drop a .csv or .txt file with your GCPs or click the + Import GCPs button and locate the file. This only needs to be done once for each project unless you collect additional GCPs at a later date.
Select a Known or Custom Coordinate System
By default, WGS 84 is selected but you can type in an EPSG codes to find your coordinate system or choose to use a Customer Coordinate System.
Confirm columns are correct
The GCP tool expects coordinates to be in x, y, z order. If the coordinates are y, x, z you will receive a warning. Change the order using the drop-downs at the top of the columns.
If using a Custom Coordinate System
Once you insert your control points you will get a new column called “Geolocate in Map”. Choose a Control Point and click in “Geolocate in Map” in that row:
You’ll get a view of the Ortho. Use the ortho to locate the control point and click on it. You need to do this process for two Control Points.
This process is used to place the GCPs over the ortho so that we are able to choose the right photos for the control point.
Tag points in photos – Smart GCPs
After uploading your GCPs turn on the Ground Control Points toggle and click on Georeference GCPS in the toolbar.
First, click on the GCP (circle with X) you want to tag in photos. The GCP’s border and X will turn blue and it will mark in light blue the photos that possibly contain the mark of the control point. Then select the photo you want to tag the GCP in. A popup with the photo will appear. You can zoom and pan to find the GCP. For best results try to tag the pixel in the middle of the GCP. Click Save once you’ve selected the middle of the GCP.
Repeat this process until the GCP is completely blue, which required four photos. You can process with fewer photos per GCP but the more the better.
Step 6 (Optional)
After tagging the photos to your GCPs, you may choose to use some control points as “Checkpoints”. Checkpoints are not used to enhance the accuracy of the outputs, they are used to independently measure the accuracy of the results by comparing the surveyed location of the control points to their location in the processed outputs.
- Checkpoints should only be used if there are at least 5 other points available to be used a Control Points (GCP).
- Checkpoints should be inside the site, not on corners.
- To obtain the most conservative accuracy value, place checkpoints as far from GCPs as possible.
- After validating accuracy with checkpoints, reprocess flight using all points as Ground Control Points to further enhance accuracy.
Sample layout for GCPs in green and Checkpoints in red:
“Ideal Ground Control and checkpoint layout on a 40 acre / 16 hectare site, using 8 GCPs and 5 Checkpoints.”
Confirm and process
After you have tagged at least two GCPs in two photos each you can process. For good results, we recommend tagging at least 5 GCPs in 4-5 photos each.
Click the Process button to process with GCPs.
Analyze and export
With georeferenced orthos Site Scan’s analysis tools become even more powerful. Overlay, compare flights, and measurements benefit from the improved accuracy of georeferencing. Additionally, your ortho, DEM, and point cloud (.las) will all be georeferenced in your desired coordinate system.