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Custom coordinate system Ground Control Point enhancements in Site Scan Manager

06-15-2021 06:10 PM
Esri Contributor

Previously, when uploading Ground Control Points (GCPs) in a custom coordinate system to Site Scan Manager, users were always asked to geolocate two of the points on the map. This allowed Site Scan to define the custom coordinate system in its backend system including placing and rotating the points on a World map. Scaling is done using the chosen units.

Occasionally, users would select approximate locations when locating their two points, because an orthomosaic had not yet been processed for example. This could introduce a rotation unintentionally when in fact the custom coordinate system was aligned with true north. This affected the accuracy of the coordinate system transformation and led to an offset when comparing the processed outputs to data that was not in the same custom coordinate system.


This June 7th, 2021 update to Site Scan Manager introduces a new option when uploading GCPs in a Custom Coordinate System called "Rotated from True North":

  • No (Default): now only 1 GCP must be geolocated, and the define Custom Coordinate System will not be rotated. This should be used when the Custom Coordinate system is not rotated from True North. Approximate geolocation of the point will not affect output accuracy. Uses Transverse Mercator projection.
  • Yes: identical to the previous process, two points must be geolocated to input the rotation of the Custom Coordinate system. This option should be used when the custom coordinate system is known to be rotated. Users should make sure to precisely geolocate two points using an already processed orthomosaic. Uses Hotine oblique Mercator projection.

Additionally, when uploading a new GCP set, users now have the option to reuse a custom coordinate system previously defined within that Site Scan Project. If this option is used, geolocating one or two points on the map is not necessary. This functionality ensures that results processed with different GCP sets in the same custom coordinate system align when viewed and analyzed in Site Scan Manager. Accuracy of the outputs when exported remains unaffected, as previously.


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