IMPORTDEM — Import DEM

Imports a digital elevation model (ASCII Grid or GeoTIFF) as a surface.

• Command: IMPORTDEM · Global name: _IMPORTDEM
• Ribbon: Topography › Terrain data

Imports a gridded digital elevation model (raster) and creates it as a surface, like SURFACE: a mesh of triangular faces on which CONTOUR works. It reads the DEMs of the Spanish CNIG download centre (MDT05, MDT25 and MDT200) and any other in ESRI ASCII Grid (.asc) or GeoTIFF (.tif).

Usage

1. Enter IMPORTDEM or click Import DEM in the Terrain data panel of the Topography tab.

DEM file (.asc or .tif):

2. Choose the file. The Import DEM dialog opens with the grid size and the coordinate system of the file.
3. Check the Source coordinate system, choose the clip and the subsampling and click OK.
4. With Window, specify the two corners; with Boundary, select a closed polyline.

Select a closed polyline as boundary:

Options

• Source coordinate system: the one stated by the file is proposed (GeoTIFF EPSG GeoKey, the .prj of the ASCII Grid or the zone in the CNIG sheet name, such as …_ETRS89_HU30_…). If the drawing has no coordinate system it adopts it; if it has another one, the data are reprojected to it, with a warning when the datum changes (for example, from ETRS89 to ED50).
• Clip and subsample: All (the whole sheet), Window or Boundary, in drawing coordinates.
• One cell of every: takes one cell of every N in rows and columns. With 0 it is chosen automatically for about 30,000 points.

Command line

After the file, the same questions as in the dialog are asked; Enter accepts the proposed value.

Source EPSG <…>:

Subsample, one of every N cells [Auto] <Auto>:

Clip [All/Window/Boundary] <All>:

Notes

• The Spanish IGN and CNIG DEMs are in ETRS89 / UTM, in the zone of the sheet (EPSG 25829, 25830 or 25831); the Canary Islands, in REGCAN95 / UTM 28. If the drawing is in ED50 (EPSG 23030…), the datum change uses the official grid when installed (see Georeferencing).
• A DWG face mesh holds at most 32,767 vertices: if the requested subsampling gives more, it is increased with a warning.
• The centre of each cell is used; cells without data (NODATA) are skipped.
• Where to download official DEMs for Spain and other countries: Map servers by country.

See also

IGNDEM · SURFACE · CONTOUR · LANDXMLIN · GEOGRAPHICLOCATION