How To: Apply a hillshade effect to a DRG


Applying a hillshade effect to a USGS DRG can be accomplished with a series of GRID operations, as shown in this document.


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.

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

You may alter the values for the SAI command (in particular the altitude) to enhance or reduce the effect of the hillshade.