Adjusting pixel values for a lake

Typically, a lake does not have features that can be used for matching during extraction of a digital elevation model (DEM). Therefore, lakes in a DEM often contain failed pixel values or incorrect elevation values.

Tip: You can also use this procedure for other DEM-editing tasks, such as neutralizing cloud-covered areas. When clouds obscure a large area over rugged or mountainous terrain, the area can sometimes be too complex to interpolate. To avoid confounding the data, you can set the entire area to the background value.

To adjust pixel values for a lake

In Focus, open the file containing the DEM you want to modify, and make sure the DEM layer is selected.
Tip: You may want to also open some reference data to help you identify the areas in the DEM to edit.
On the Maps tab, make sure the DEM layer is selected.
Click the Layer menu, and then click DEM Editing.
The DEM Editing window appears.
To work with a bitmap mask, do the following; otherwise, proceed to step 4:
1. In the DEM Editing window, click the Edit via Bitmap tab.
2. Click Create Mask Layer.
  For more information on creating a mask layer, see Creating a new bitmap-mask layer.
3. Click New Polygon, and then draw a bitmap over the lake to be updated.
4. Under Area Fills Under Mask, in the Method list, click Specified Value.
5. In the Value box, type a value for the lake elevation.
6. Click Fill.
If you want to remove the contents of the mask, click Clear Layer. To save the layer, click Save.
To work with a vector mask, do the following:
1. In the DEM Editing window, click the Edit via Polygons tab.
2. Click Create Polygon Layer.
  For more information, see Creating a new vector-mask layer for details.
3. Click New Polygon, and then draw a polygon over the lake to be updated.
4. In the Operations list, click Constant Elevation
5. In the Elev. (Elevation) box, type a value for the lake elevation.
6. Click Apply.
If you want to discard the mask layer, on the Maps tab, right-click the layer you want, and then click Remove from Area. To save the layer, click Save.