Difference between Ground Control Points (GCPs) and Check Points

Introduction

It is common in photogrammetry and airborne LiDAR to use control points and check points, since they are essential to ensure the accuracy and reliability of spatial data. Although they may appear similar, each serves a distinct function within the data acquisition and validation workflow. This short article will explain the difference.
It is possible to use the inside LP360 in the following workflows:

• Control Points Report

• TVGO TGCP workflow

Control Points

Control points, often referred to as Ground Control Points (GCPs), are accurately surveyed locations on the ground with known coordinates, typically obtained through GNSS (Global Navigation Satellite System) measurements. These points are used during the data processing stage to georeference imagery or LiDAR point clouds, aligning them correctly within a global coordinate system. Control points also play a critical role in vertical bias correction, helping ensure that elevation data corresponds precisely to real-world heights. Their inclusion reduces both systematic and random errors, improving the overall model fidelity.

Check Points

Check points, by contrast, are independent reference locations that are not used during the processing phase. Their main purpose is to validate the accuracy of the final dataset. By comparing the model to these independent ground-truth measurements, surveyors can compute Root Mean Square Error (RMSE) values to quantify positional accuracy. These results are then used for accuracy reporting, confirming that the processed data meets industry standards.

Summary

In essence, control points guide and correct the model during processing, while check points evaluate its accuracy after completion. Together, they form the foundation of reliable, high-quality geospatial data production.

📚 Reference

Learn more about the difference and how to use them in the ASPRS Positional Accuracy Standards for Digital Geospatial Data (2024)