Someone sent me a question about a month ago asking how they could get a first-return lidar DEM out of the Digital Coast Data Access Viewer (DAV). I thought that should have been pretty obvious, but I’d make some screen shots and show them how to do it. It turned out that it wasn’t as obvious as I’d thought and was perhaps worth a GeoZone post. In case you’re wondering why you’d want only the first returns from a lidar survey, those are going to be the points that best represent the top of the canopy, buildings, etc.
Once you’ve picked your lidar datasets in DAV and started the checkout procedure, you’ll need to check the box that lets you edit all the output options (see figure 1). Until you check that box, everything else on the page is grey and you’ll only get the default choices.
Once you’ve got some options to work with, you’ll also need to check the box near the bottom to “Use Advanced Options.” You’ll probably have to scroll down on the page a little bit to see all the options, as in figure 2. Now you’ll see a drop down menu for “Return Types.” One of the choices will be “First” if the data have multiple returns. Select it and your outputs will only use first returns.
That’s all there is to it. We’ll be starting work on revamping the DAV soon, so if you’ve got ideas for improvements or features you’d like to make sure remain, please put in a comment to let us know.