Are You Placing GCPs Correctly?
Best Practices for GCP Placement:
- Distribute GCPs evenly throughout the survey area—across both horizontal and vertical extents.
- Include multiple elevations, elevated features (e.g., berms, benches) and lower areas (e.g., pit floors), while placing GCPs to help fixing the model in 3D space more effectively.
- Use at least 3–10 well-distributed points, depending on the size of the area.
- Ensure each GCP is clearly visible in multiple images from different angles (minimum 3–4 images).
- Mark GCPs clearly using checkerboards or contrasting targets so that they can be easily and precisely marked during processing
| Aspect | Good Practice | Common Mistake |
| GCP Quantity | 3–10+ spread across site | Too few GCPs |
| Vertical Placement | Include multiple elevations | Placing GCPs on similar elevations |
| Surveying | Use RTK/PPK for high precision | Low-accuracy GPS or manual estimates |
| Image Coverage | GCP visible in 3–4+ images | Poor visibility / edge of images |
| Marking Accuracy | Zoom in and mark precisely | Rough or inconsistent marking |
How GCPs used in ShapeMetriX Referencing Workflows?
In ShapeMetriX, GCPs are incorporated during the image alignment and scaling phase and their usage depends on the referencing workflow users choose.
Referencing Workflow:
- After loading data and setting parameters, ShapeMetriX generates the full 3D model (coarse + dense reconstruction).
- In the final step, externally surveyed GCPs are used to reference the model.
- The user marks GCPs in the images after reconstruction.
- ShapeMetriX performs a final geo-referencing step, aligning the model to the surveyed coordinates.
Note: The absolute accuracy of the final model is only as good as:
- The surveying accuracy of the GCP coordinates.
- The precision with which GCPs are marked in the images.
