## DESCRIPTION

Outputs raster maps in VTK-ASCII format. Map's are valid raster map's in the current mapset. output is the name of an VTK-ASCII file which will be written in the current working directory. If output is not specified then stdout is used. The module is sensitive to region settings (set with g.region).

Elevation, scaling, point/celldata, vector and RGB Data are supported. If the map is in LL projection, the elevation values will automatically scaled to degrees. It is supposed that the elevation values are provided in meters. If the elevation values are in a different unit than meters, use the scale parameter to convert the units.

If no elevation map is given, the user can set the height of the map by one value. Point or cell data are available. Also scaling is supported for this elevation value. The elevation value must be provided in meters.

The RGB input requires three raster maps: red, green, blue - in this order. The maps must have values between 0 and 255, otherwise you will get lots of warnings and the values are set to 0. More than one RGB dataset (3 maps) is not supported.

The vector input requires three raster maps: x, y, z -- defining the vector coordinates - in this order. More than one vector dataset (3 maps) is not supported.

## NOTES

This filter generates:

- structured points with celldata or pointdata if no elevationfile is given
- structured grid (not recommendet) with pointdata if an elevationfile is given
- polydataset with pointdata if an elevationfile is given (default)

and puts this in a simple VTK-ASCII file. Nor XML or binary output are supported. It is possible to choose more then one raster map to be written to the VTK-ASCII file. Each cell-/pointdata is named like the raster map it represents. You can visualize this file with the VTK Toolkit, Paraview and MayaVi which are based on VTK. If you have a raster map with partly no data, use the threshold filter in paraview to visualize the valid data. Just filter all data which is greater/lesser than the chosen null value in the VTK-ASCII file.
If elevation map is chosen, a polygonal grid is created with quads, but the user can choose also triangle strips or vertices. These dataformats a documented at VTK Toolkit.

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 center point of the default region).

### Difference between point- and celldata

r.out.vtk can export raster cells with different representations.

- pointdata -- the cells/values are represented by the center of the cell. Instead of cells, points are created. Each point can hold different values, but the user can only visualize one value at a time. These points can be connected in different ways.
- celldata -- is only provided if no elevation map is given. The cells are created with the same hight and width as in GRASS. Each cell can hold different values, but the user can only visualize one value at a time.

## EXAMPLE

### Simple Spearfish example

    # set region
    g.region n=4926970 s=4914857 w=591583 e=607793 res=50 -p

    # export the data
    r.out.vtk input=elevation.10m,slope,aspect elevation=elevation.10m output=/tmp/out.vtk

    # visualize in Paraview or other VTK viewer:
    paraview --data=/tmp/out.vtk

### Spearfish example with RGB data

    #set the region
    g.region n=4926990 s=4914840 w=591570 e=607800 res=30 -p

    # using r.in.wms to create RGB data to get a satellite coverage
    r.in.wms layers=global_mosaic mapserver=http://wms.jpl.nasa.gov/wms.cgi \
             output=wms_global_mosaic

    # export the data to VTK
    r.out.vtk rgbmaps=wms_global_mosaic.red,wms_global_mosaic.green,wms_global_mosaic.blue \
              elevation=elevation.10m output=/tmp/out.vtk

    # visualize in Paraview or other VTK viewer:
    paraview --data=/tmp/out.vtk

Paraview RGB visualization notes
To achieve proper RGB overlay:

- In Paraview, click "Apply"
- Select the "Display" tab and choose "Color by" to switch from input scalars to rgb scalars
- Disable the "Map Scalars" check button in the display tab to avoid the use of a lookup table

## SEE ALSO

r3.out.vtk, r.out.ascii, g.region
GRASS and Paraview Wiki page

## AUTHOR

Soeren Gebbert

Last changed: $Date: 2014-11-28 15:27:47 +0100 (Fri, 28 Nov 2014) $