Create a 2-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

Specify the colour zoning method for rendering colour distributions. Select one of the options below:

  • As last displayed: the grid is displayed in its last viewed state: its previous colour transform is used, and the currently selected colour scheme will be ignored.

  • Default: the default colour distribution method is used.

  • Histogram equalization: your data values are evaluated, and the zones are statistically determined, such that data is equally divided among the histogram bins.
  • Normal distribution: your data is assumed to be normally distributed, and the zones are determined based on the standard distribution for a standard bell curve.
  • Linear: the range of data values are divided linearly into even increments.
  • Log-Linear: the zone values are updated based on the log distribution of the data, and the data is displayed using the log-linear colour distribution.

  • Shaded relief: the grid is displayed as a shaded relief image.

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:

  • As last displayed: the grid is displayed in its last viewed state: its previous colour transform is used, and the currently selected colour scheme will be ignored.

  • Default: the default colour distribution method is used.

  • Histogram equalization: your data values are evaluated, and the zones are statistically determined, such that data is equally divided among the histogram bins.
  • Normal distribution: your data is assumed to be normally distributed, and the zones are determined based on the standard distribution for a standard bell curve.
  • Linear: the range of data values are divided linearly into even increments.
  • Log-Linear: the zone values are updated based on the log distribution of the data, and the data is displayed using the log-linear colour distribution.

  • Shaded relief: the grid is displayed as a shaded relief image.

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)