How to add two grids together

Mapper has the functionality to add two grids/DTM together. The procedure is as follows:

1.   Load the required grids into the viewport by clicking the ‘Add GIS Data’ button from the Home menu. 

2.   Double click on the Superimpose Grid tool which can be accessed from the Toolbox. This will open a new window with the available grids as shown below.

3.   Choose a Base Grid. This serves as the primary grid input.

4.   Choose an Additional Layer. This serves as the secondary grid input.

5.   Choose the impose methods:

a.   Output Extent:

·       Combine boundaries – the extent of the output will be the combined extents of the base and additional grid inputs.

·       Use base grid boundary – the extent of the output will be the same as that of the base grid input.

b.   Superimpose option

·       Replace all base data – superposition of the two grids will be performed and applied to all cells within the specified output extent.

·       Replace NoData only – superposition of the two grids will be applied only to NoData cells in the base grid within the specified output extent.

c.   Output File

·       Replace existing base grid – the output of the superposition of the two grids will overwrite the existing base grid.

·       Create new grid – the output of the superposition of the two grids will be written in a new file.

6.   Use the browse button in the output grid box to specify the name and the location of the new grid file to be created by the tool. Output format can be either binary (flt) or ASCII (asc) formats. In addition an option is provided for the tool to automatically load the new grid file into the Flood Modeller viewport when the calculation process is complete.