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v.out.vtk(1grass) GRASS GIS User's Manual v.out.vtk(1grass)


v.out.vtk - Converts a vector map to VTK ASCII output.


vector, export, output, VTK


v.out.vtk --help
v.out.vtk [-cn] input=name [layer=string] [output=name] [type=string[,string,...]] [precision=integer] [zscale=float] [--overwrite] [--help] [--verbose] [--quiet] [--ui]


Correct the coordinates to fit the VTK-OpenGL precision

Export numeric attribute table fields as VTK scalar variables

Allow output files to overwrite existing files

Print usage summary

Verbose module output

Quiet module output

Force launching GUI dialog


Name of input vector map
Or data source for direct OGR access

Layer number or name
Vector features can have category values in different layers. This number determines which layer to use. When used with direct OGR access this is the layer name.
Default: 1

Name for output VTK file

Input feature type
Options: point, kernel, centroid, line, boundary, area, face
Default: point,kernel,centroid,line,boundary,area,face

Number of significant digits (floating point only)

Scale factor for elevation
Default: 1.0


v.out.vtk converts a GRASS vector map in binary format to the VTK ASCII output.

If the output parameter is not given, the output will be send to stdout.


The following vector types can be exported together in one VTK ascii file:

  • point
  • line
  • centroid
  • boundary
  • area
  • face
Category data (cat) for the selected vector type and layer will be written as scalar data with name "cat_{vectorname}". If no cat exists, the value will set to -1 as normal cat’s are always positive. If a vector has more categories in one layer, only the first category will be exported.
3d vectors are supported by default. The created VTK data always includes x, y and z coordinates (z = 0 if not a 3d vector map). Note that you can easily convert your 2d vectors into 3d vectors with v.drape.
Because of the 32bit limits of OpenGL which is used by VTK, visualisation errors may occur if the grass region contains coordinates greater than 1.000.000 and vector coordinates with 0.01 - 0.001 meters precisison. For this reason, the flag "-c" was added. The coordinates are transformed to smaller coordinates (by decreasing the coordinates with the region center).
If the "-c" flag is used and the data should be visualised together with other data exported via *.out.vtk modules, be sure the "-c" flag was also set in these modules. But this will only work with data from the SAME location (The reference point for the coordinates transformation is based on the default region).
The GRASS vector data is converted into the polydata format of VTK:
  • vtk Vertices -- representing points and centroids
  • vtk lines -- representing lines and boundaries
  • vtk polygons -- representing areas and faces

The VTK file can be visualized with VTK Toolkit, Paraview and MayaVi.


If areas or faces are exported, the data have to be triangulated within Paraview or MayaVi.


Spearfish example:

Export the soils with cats in layer 1:

v.out.vtk input=soils type=area layer=1 output=/tmp/soils.vtk
Export the streams with cats in layer 1:
v.out.vtk input=streams type=line layer=1 output=/tmp/streams.vtk
Write the archsite vtk output to stdout with cats in layer 1:
v.out.vtk input=archsites type=point layer=1




Soeren Gebbert


Available at: v.out.vtk source code (history)

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© 2003-2020 GRASS Development Team, GRASS GIS 7.8.5 Reference Manual

GRASS 7.8.5