These coordinates describe the geographic footprint of the 3D terrain model exported from demo3d.
Two coordinate systems are shown: WGS84 (universal GPS standard) and Lambert-93
(the French national grid used in the source data).
Centre
The geographic centre of the model's bounding box, in decimal degrees (WGS84).
This is the point Google Earth and the IGN map zoom into by default.
Format: latitude° N, longitude° E
SW / NE corners
South-West and North-East corners of the rectangular footprint.
Together they define the bounding box of the printed terrain model.
The Lambert-93 values below are the original coordinates from the demo3d export file.
Lambert-93 is a metric projected CRS (EPSG:2154) — values are in metres from a French national origin.
Footprint size
Real-world dimensions of the terrain covered by the model, in metres.
A 2 000 × 2 000 m footprint at scale 1:8 000 produces a 250 × 250 mm physical model.
Formula: footprint (m) ÷ scale = print size (mm)
Base altitude (z_base)
The lowest elevation kept in the model, in metres above sea level (NGF-IGN69 datum).
The terrain is "sliced" at this altitude to create a flat base for the physical print.
All vertical relief is measured relative to this value.
Scale
The ratio between the printed model and reality. 1:8 000 means 1 mm on the model = 8 m in the field.
Horizontal and vertical scales are equal (Z scale × 1.0 = no vertical exaggeration).
Z scale
Vertical exaggeration factor applied to the model. × 1.0 means the relief is true-to-scale —
heights are neither stretched nor compressed compared to the horizontal dimensions.
Values above 1.0 would make mountains look taller than they really are.
Coordinate systems
WGS84 (EPSG:4326) — global GPS standard, used by Google Maps, Google Earth, and this map.
Coordinates are decimal degrees of latitude and longitude.
Lambert-93 (EPSG:2154) — French national projection, used by IGN and in the demo3d source files.
Coordinates are in metres (Easting / Northing).
Conversion between the two systems is performed using the pyproj library.