Ground Control And Check Shots in Pix4D

Discusses the difference between ground control points and check shots and how to use each of them in Pix4D to obtain survey grade accuracy
Attributes of GCPs and Check Points
(1) GCPs are used to rotate, scale and orientate the project in a real world location or in some cases in a "Local Coordinate System)
(2) GCPs are typically statically placed around the outside edge of the project with at least one GCP in the interior of the project
(3) GCPs should not be more than 1,000-1,500 feet apart
(4) Check Points are used for independent verification of the accuracy of your project
(5) Check Points are randomly spaced throughout the project
Types of Ground Control Points
(1) 3D Points (X, Y, Z)
(2) 2D Points (X, Y) (no elevation information)
(3) Z only (not applicable for Drone work)
Types of Check Points
(1) All the same types as GCPs
(2) The Z is very important for elevation verification
Format of GCPs
(1) Standard format is X, Y, Z. Used mainly by non-surveyors
(2) Northing, Easting, Elevation (Y, X, Z) is commonly used by surveyors
(3) Latitude, Longitude Elevation (Y, X, Z) is the native output from most survey grade GPS systems. The elevation is generally not is generally not Mean Sea Level (ellipsoid elevation).
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