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Control Points (GCPs and CHPs) File Format for Data Processing


We’ve made it as easy as possible for you to upload your control point coordinates no matter what type of control point marker you use. All you need is a simple text file, in addition to your photos, for processing. You or your survey team will be able to create this text file in a couple of minutes!

Our Skycatch data processing pipeline accepts two types of control points: ground control points (GCPs) and checkpoints (CHPs).

  1. GCPs are used during the data processing step to accurately georeference and calibrate your images.
  2. Checkpoints (CHPs) are not taken into account for processing and calibrating your models; CHPs’ coordinates are used to assess the accuracy of your project by comparing its true predetermined locations with the positions of processed ground control points. CHPs help you see the amount of error in a project.

Here are a few notes about using control points with Skycatch:

  1. The coordinate system you define for your site and the coordinate system for your control points must be the same. They should either both be in a GPS coordinate system (lat,lng,alt) or in a planar coordinate system (x,y,z).
  2. Control points should have survey grade coordinates as this will have a high impact on the accuracy of the data processing.
  3. You may use your own control point markers or use Skycatch control point markers. The advantage of using Skycatch control point markers is that we use computer vision to automatically detect and mark them in pre-processing. Download the printable files for Skycatch control points here.
  4. If you are not using Skycatch control point markers, you must manually upload and mark your control points by following these instructions.
  5. Our control points marking tool is only available to HPP and premier plan customers. If you’re interested in trying out the marking tool, let us know at support@skycatch.com.

Control Points processing with local coordinates

You can submit control points in a GPS coordinate system (lat/lng/alt) or a planar coordinate system (x,y,z) in our web uploader. If you are using local coordinates, the site coordinate system can consume a localization file (.tp3 or .gc3). You can verify that the coordinates are in the correct location when reviewing the data before upload - the control points and the photos should be in the same location.

Using local coordinates to specify the site coordinate system is a feature that is only available to our HPP customers. If you’re interested, we’d be happy to tell you more about the HPP plan. Please email us at support@skycatch.com, or learn more about the HPP plan here.  

Save your Control Points File with a .csv file extension

The uploader only accepts a .csv file extension for control points. Mac users can right click a file folder and select "Rename" to rename the file extension. Windows users can follow the instructions provided here to rename their file extensions.

How to Format Data In Your Control Points File

The control points file must have .csv as the file extension and a header line formatted as:

            a. If using Skycatch control point markers and ID tags: "name, type, y, x, z, tag” or “name, type, lat, lng, alt, tag”

            b. If not using Skycatch control point markers and ID tags): “name, type, y, x, z” or “name, type, lat, lng, alt”

The following 6 columns of information should be in each file:

1. "name" - the name of the control point

2. “type” - GCP or CHP

3. "y" or "lat" - Northing or Latitude value

4. "x" or "lng" - Easting or Longitude value

5. "z" or "alt" - Orthometric Height (Elevation) or Height above the ellipsoid

6. "tag" - If not using Skycatch control point marker, this “tag” column should not be in your file.

If using Skycatch control point markers: The tag ID number in the “Add Control Points" step of the upload process is the ID number located in the lower right hand corner of each Skycatch control point. 

 

Control points file examples

Here is an example of a .csv control points file in a GPS coordinate system, with Skycatch control point marker ID tags:

You can download the following example files to use as a template for formatting your control points. Simply replace the data under the headings row with your own data.

  1. Skycatch Tags, GPS Coordinates Example.csv
  2. Skycatch Tags, Planar Coordinates Example.csv
  3. No Skycatch Tags, GPS Coordinates Example.csv
  4. No Skycatch Tags, Planar Coordinates Example.csv
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