Cartographic projection in VisIt

VisIt (as of version 2.6) will provide a transform operator to apply cartographic projections to 2D grids. The input can be an image file, conveniently displayed with the TrueColor plot, and then mapped, or a spherical shell, e.g. the result of an Extract Subset on a 3D (R,Theta,Phi) grid, or a 2D grid often found in netcdf databases.

The projection is implemented via VTK's libproj4 library, which implements the cartographic projections. See the PROJ.4 page for more details.

The input is expected to be a 2D VtkStructuredGrid or vtkRectilinearGrid with longitude ranging from -180 to 180, and latitude ranging from -90 to 90 degres. If your data has a different range, you must scale and translate it first before applying the projection. In the example below, we used an image file of pixels resolution (xres, yres). Pixels in the TrueColor plot are assumed to be square, so a scaling by [360.0/xres, 180.0/yres, 1.0] in [x,y,z] was applied + a translation by [-180.0, -90.0, 0.0].

Not all projections are currently available, to simply keep the pull-down menu smaller. If you need a specific projection, please ask on the mailing list.

Examples of some standard projections

Mollweide projection Winkel II projection Hammer projection Eckert IV projection Aitoff projection