Lighting effects can provide important visual cues when elevation maps are combined with other kinds of data. The shading resulting from lighting a surface makes it possible to "drape" satellite data over a grid of elevations. It is common to use this kind of display to overlay georeferenced land cover images from Earth satellites such as LANDSAT and SPOT on topography from digital elevation models.
When the elevation and image data grids correspond pixel-for-pixel to the same geographic locations, you can build up such displays using the optional altitude arguments in the surface display functions. If they do not, you can interpolate one or both source grids to a common mesh.
The geoid can be described as the surface of the ocean in the absence of waves, tides, or land obstructions. It is influenced by the gravitational attraction of denser or lighter materials in the Earth's crust and interior and by the shape of the crust. A model of the geoid is required for converting ellipsoidal heights (such as might be obtained from GPS measurements) to orthometric heights. Geoid heights vary from a minimum of about 105 meters below sea level to a maximum of about 85 meters above sea level.
If you want to combine elevation and attribute (color) data grids that cover the same region but are gridded differently, you must resample one matrix to be consistent with the other. That is, you can construct a geolocated grid version of the regular data grid values or construct a regular grid version of the geolocated data grid values.
It helps if at least one of the grids is a geolocated data grid, because their
explicit horizontal coordinates allow them to be resampled using the
geointerp function. To combine dissimilar grids, you can do
one of the following:
The following two examples illustrate these closely related approaches.