Georeferencing
Tie the project to a real-world coordinate system, and reconcile grid distances with ground distances.
Setting a coordinate system
Tools › Coordinate System assigns a CRS by EPSG code or PROJ/WKT definition. The CRS is saved with the project and shown in the status bar. Without one, the project is in local coordinates and scale-factor calculations are off.
Grid vs ground
A map projection necessarily distorts distance, and a measurement taken at elevation is longer than its projection onto the ellipsoid. So a distance has two values:
- Grid distance — the distance in the projected coordinate system (what your coordinates give).
- Ground distance — the true distance on the terrain (what you'd measure with a tape).
They are related by the combined scale factor:
grid = ground × combined · combined = kgrid × kheight
kgrid = projection distortion (from the CRS) · kheight = R / (R + H), R = Earth radius, H = elevation.
Where it shows up
| Place | What you see |
|---|---|
| Status bar | Grid and combined scale factors at the cursor; selected alignment's grid and ground length (with the mm/km difference). |
| Distance Inquiry (Grid/Ground)… | Distance between two points reported both as grid and ground. |
| Scale Factor Report… | A heatmap and statistics of the scale factor across the project area. |
Why it matters
For setting-out and quantities over long projects, the grid/ground difference
is real — kilometres of alignment can differ by metres. yucad3d keeps both
numbers in front of you so you never set out the wrong one.
The scale-factor formulas are in the Formula reference.