Create a Two-grid Composite

Use the Grid and Image > Display on Map > 2-Grid Composite menu option (GRIDIMG2 GX) to place an aggregate of two grid images on a map. The tool is typically used to create shaded relief maps and allows you to input two separate colour tables to display together to provide different colour effects.

2-Grid Composite dialog options

Grid 1 name

Select the first grid name.

Script Parameter: GRIDIMG2.GRID1

Colour method

Select the colour method as one of the following options: As last displayed, Default, Histogram equalization, Normal distribution, Linear, Log-linear.

  • The method "As last displayed" will display each grid as it was displayed the last time the grid was viewed, and the colour tables will be ignored.
    If the selected colour scheme is an .itr file or a .zon file, the colours are already attributed to data ranges, and this entry remains disabled.

    • Script Parameter: GRIDIMG2.ZONE1

    Colour table

    Select the colour scheme for rendering the image of the first grid. If you mouse over the colour scheme entry, a tooltip will display the name of the colour table in its folder. To modify the selection, click on the colour entry and then navigate through the scheme categories.

    Script Parameter: GRIDIMG2.COLOR1

    Contour interval

    Specify the contour interval for the selected grid.

    Script Parameter: GRIDIMG2.CONTOUR1

    Grid 2 name

    Select the second grid name.

    Script Parameter: GRIDIMG2.GRID2

    Colour method

    Select the colour method for the second grid, "Default/Last", "Histogram equalization", "Normal distribution", "Linear", "Log-Linear" or Shaded relief". The "Default/Last" method will display the grid as it was displayed the last time the grid was viewed and the colour table will be ignored.

    Script Parameter: GRIDIMG2.ZONE2

    Colour table

    Select the colour scheme for rendering the image of the second grid. If you mouse over the colour scheme entry, a tooltip will display the name of the colour table in its folder. To modify the selection, click on the colour entry and then navigate through the scheme categories.

    Script Parameter: GRIDIMG2.COLOR2

    Render method

    Select the render method.

    ADD - All the colours are added together.

    BLEND – All the colours are added then divided by the number of valid (non-dummy) colours.

    BLEND EQUAL – All the colours are added then divided by the number of colours.

    Script Parameter: GRIDIMG2.METHOD

    Application Notes

    Click the New Map button to display a grid on a new map. Click the Current Map button to display the grid on the current map. (For a script file, set 'Script Parameter: GRIDIMG2.NEW' to 1 to create a new map or 0 to use the current map). If a new map is specified, the range of the grid is used to create a basic map layout. The MAPSET GX is called to create the new map.

    A standard configuration is to use the COLOUR.TBL for Grid 1 and the LGREY.TBL for Grid 2.

    When using ER Mapper ternary colour images, the band numbers should be specified for each colour grid.

    As an example, for an ER Mapper file named "Weshade.ers(ERM)", the following should be entered in the three colour bands:

    Red-Cyan grid Weshade.ers(ERM;band=0)

    Green-Magenta grid Weshade.ers(ERM;band=1)

    Blue-Yellow grid Weshade.ers(ERM;band=2)