Ground Control Point Placement Guide & Field Log
Place ground control points correctly and record their coordinates in the field. Poor GCP distribution is one of the most common causes of a warped or mis-scaled model. Use the placement rules to lay out control, then record every point in the field log so nothing is lost between site and desk.
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Ground Control Point Placement Guide & Field Log
Place ground control points correctly and record their coordinates in the field. Poor GCP distribution is one of the most common causes of a warped or mis-scaled model. Use the placement rules to lay out control, then record every point in the field log so nothing is lost between site and desk.
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Why GCP placement decides your accuracy
Ground control points tie a photogrammetric model to real-world coordinates and hold its scale and shape. Where they are placed matters as much as how accurately they are measured: control clustered in one area lets the far side of a model drift and bow. Spreading control to the edges and corners of the survey area, and varying its height, is what keeps a model true.
Placement rules
| Rule | Why it matters |
|---|---|
| Distribute to the edges and corners of the area | Prevents the model bowing or dishing away from control |
| Vary GCP height where the site has relief | Controls vertical scale, not just plan |
| Keep targets flat, matte and clearly visible | Glossy or creased targets are hard to pick precisely |
| Each GCP visible in at least 3–5 images | A point seen in too few images cannot be solved reliably |
| Reserve check points not used in alignment | The only honest measure of achieved accuracy |
| Avoid placing on loose or moveable objects | A shifted target corrupts the whole solve |
How many control points
| Project type | Minimum GCPs | Check points |
|---|---|---|
| Single façade / small structure | 5 | 2–3 |
| Full building exterior | 8–10 | 3–4 |
| Site or campus (drone) | 10–15+ | 4–6 |
| RTK/PPK drone with good base | 4–6 (verification) | 3–4 |
GCP field log
| GCP ID | Description / location | Easting / X | Northing / Y | Elevation / Z | Method |
|---|---|---|---|---|---|
Check point log
| CP ID | Description | Easting / X | Northing / Y | Elevation / Z | Residual (mm) |
|---|---|---|---|---|---|
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