Apply a hillshade effect to a DRG

The basic procedure is to generate the hue and saturation layers from the DRG grid with the COLOR2HUE and COLOR2SAT functions, and the value layer from the COLOR2VAL function on the hillshade grid.

For the hillshade component, you can use the results from HILLSHADE on the elevation grid. However, you may get better results using the SAI command.

Finally, use the GRIDCOMPOSITE HSV command to combine the color information of the DRG with the grey hillshade effect.

The following example illustrates this procedure. The elevation grid is called 'reddem' and the DRG is 'drgutm'. Note that DRGs are usually available in higher resolutions than elevation datasets, so the example includes steps to address this.

Code:
  Grid: SETWINDOW reddem
  Grid: SETCELL drgutm
  Grid: drgclip = drgutm
  Grid: demmean = FOCALMEAN (reddem)
  Grid: &DESCRIBE drgclip
  Grid: demhires = RESAMPLE (reddem, %GRD$DX%, BILINEAR)
  Grid:
  Grid: hue = COLOR2HUE (drgclip, drg.cmap)
  Grid: 
  Grid: sat = COLOR2SAT (drgclip, drg.cmap)
  Grid:
  Grid: SAI demhires demsai
  Grid: SAI sai60.cmap 315 60
  Grid: val = COLOR2VAL (demsai, sai60.cmap)
  Grid:
  Grid: GRIDCOMPOSITE HSV hue sat val