Generate contour lines as DXF, from IGN data

Pick the parcel and the interval: GeoAlt computes contours on the real relief and exports them as DXF 3D, elevations included.

Contour lines turn relief into CAD-usable lines: every polyline carries its elevation, and the plan becomes readable for an earthworks contractor as for an architect. GeoAlt computes them on demand from IGN elevation models and delivers them as DXF 3D.

What usually gets in the way

Elevation models that need rework

Public elevation models arrive as geotiff tiles or raw clouds: they must be assembled, filtered, then run through contour computation in a GIS.

Contours without true elevations

A DXF whose polylines are flat (Z = 0) forces manual elevation entry: the file loses its CAD value.

A fixed contour interval

Flat or steep ground, study or execution: the useful interval changes. An export locked to one value does not fit every use.

The GeoAlt computation

Interval of your choice
From a fine interval on flat ground to wide steps on a slope: the interval is a computation parameter, not a hidden option.
DXF 3D with true elevations
Every polyline carries its Z in the territory’s coordinates (Lambert 93 and IGN 69 vertical datum for mainland France): the file opens directly in AutoCAD, BricsCAD or Illustrator.
Preview before export
Contours render on the map, overlaid on the parcels and the orthoimagery: adjust the interval before paying for the export.
LiDAR class filtering
The terrain model can exclude vegetation and buildings (LiDAR classes) for ground contours, or include them for a surface model.
Generate contour lines as DXF, from IGN data
The public demo computes contour lines on a real parcel and shows the resulting DXF export.

Try it on a real parcel

The public demo computes contour lines on a real parcel and shows the resulting DXF export.

Open the demo

Supported formats

  • DXF 3D (3D polylines, true Z)
  • SVG for layout
  • PDF plan with overlaid contours

Stated technical limits

  • Contours follow the source model resolution: 1 m grid (RGE ALTI) or local LiDAR HD density.
  • In areas covered only by RGE ALTI, no class filtering: the surface model includes buildings and tall vegetation.
  • Contours are not a boundary-staking document.

Frequently asked questions

Is the DXF AutoCAD-compatible?

Yes: standard 3D polylines, Lambert 93 coordinates, elevations in metres. The file also opens in BricsCAD, QGIS and most DXF viewers.

Which interval should I choose?

0.25 to 0.50 m for flat ground or a platform, 1 m for rolling terrain, 2 to 5 m for a slope. The preview lets you judge before exporting.

Do contours follow the ground or the surface?

Your choice: LiDAR class filtering gives a ground model (ground only) or a surface model (ground, buildings, vegetation).

Can I bring the contours into SketchUp?

Yes: the DXF imports into SketchUp Pro, and the Sandbox “From Contours” tool builds the 3D terrain from the polylines.

Compute your contour lines

Enter a cadastral reference, choose the interval, preview, then export the DXF.

Open the application