I am looking for a way to adjust/edit the values in a DEM file, for example, to grade a detention pond and berm into existing LiDAR data. I have tried messing around with point shapefiles and the IDW tool, but I am wondering if there is a better way. I can provide any additional details as needed.
QGIS has a simple and effective plugin named "Serval" that I believe will help you out. To install Serval, select Plugins > Manage and Install Plugins > All > and scroll down to Serval, and click the Install Plugin button. A Serval toolbar section is thus created.
Using Serval is pretty straightforward. It has 3 modes:
Probing: Use this mode to change the value of a single cell. Click on a cell with the eyedropper cursor. The cell's band value(s) will be displayed in the Serval toolbar spinbox(es). Type in a new value(s) and - Voila! - the cell is updated.
Drawing: This mode is useful if you need to adjust multiple cells to the same value(s) (for example, you want to set all the cells in your detention pond to the same elevation). Select the Serval Drawing button and then enter the new value(s) in the spinbox. With the pencil cursor, click on those cells that are to receive the new value(s) and - Voila! - the cells are updated.
Erasing: When this mode is selected, clicked cells are set to the raster's NoData value.
The Serval toolbar has undo and redo buttons. However, if you exit the QGIS project, all changes are immediately applied to your raster. Thus, it is a good idea to make a copy of your raster prior to using Serval.
There is a similar product for the Arc Desktop environment: ARIS Grid and Raster Editor. However, it costs $400, and that's on top of the price to purchase Arc Desktop.
I've used Serval and ARIS, and they both get the job done just fine.
If you are using ESRI products and you have point data with the proposed final elevation values of your project you can create a TIN from those points. Convert the TIN to a raster. Then replace that portion of the DEM with the raster version of your berm and pond. There is a lot of help to get you there online and these steps use standard tools.
Some considerations are:
- Ensure that your points use the same vertical datum as your LiDAR.
- Build a polygon that represents the extent of the proposed construction to act as a barrier (hard polygon in TIN speak) to limit the TIN and resulting raster to the extent of the project.