Procedure Library for Changing Grid Elevation Values.

The purpose of this procedure library is to explain how to change the elevation value from meters to feet, for example, in a DEM grid. This is necessary because the Project Grid function in Arctools does not successfully convert the elevation to feet.

Andy Freed

6/1/2001

Tools: ArcView 3.2, Map Calculator, 3D Analyst

This procedure requires that you have your DEM in grid format.

Open the Grid

· Make sure 3D Analyst is loaded.

· In a View, add the grid you want to modify

Use Map calculator

· Select the grid theme

· Open the Map Calculator by selecting Analysis/Map Calculator

· Select the Grid you opened from the layers list.

· In the equation below, multiply the theme by 3.28 (for meter to feet) or any conversion factor you desire. (GridLayer) * 3.28

· Click Evaluate

Save New Grid

· A new grid will appear in the View, Choose Convert to grid from the Theme menu.

· Save the grid with a recognizable name, possibly something that will signify the fact that it uses a different elevation unit.

Create a TIN

· If you want to create a TIN (Triangulated Irregular Networks) with the new Grid, now is your chance.

· With the grid selected, choose Convert Grid to TIN from the Theme menu.

· Save the TIN, and choose a Z-tolerance value in z-units (feet). I chose 5 feet because I wanted a detailed TIN file to work with.

· Wait.

Modified 6/1/2001

For additional Information, see the 3D Analyst manual from ESRI.