ArcGIS Terrains

Tuesday, 22 July, 2008

ESRI have been busy bees in the 3D geospatial world and one of the “new” features in ArcGIS 9.2 (OK, I know 9.2 isn’t that new with SP5 out and 9.3 imminent!) is the ability to create “Terrains”. Clearly ESRI realise that a huge new sector of data capture is via LiDAR (initially airborne, but increasingly terrestrial) and given that performance in ArcGIS (generally) is, as Ian would say, as good as a chocolate teapot, they needed to come up with some ways of improving data visualisation (re-drawing speeds). Not only that, but given that many people don’t use server-side databases, the personal geodatabase was increasingly looking long in the tooth, using a bespoke format, and just not designed for the job (i.e. it can’t store more than 2Gb). LiDAR, and more generally raster, data can surpass this limit quite quickly.

So terrains have been born that essentially take the idea of pyramid layers (i.e. subsampling) and applies it to vector data. And by vector data we are primarily talking about LiDAR point clouds and their conversion to TINs, but that then can include things like breaklines, drainage, masks etc etc. So its not exactly revolutionary but very much a step in the right direction. The ESRI Instructional Series has two useful introductions on terrains.

And to create them? Well you need 3D Analyst installed and, you would hope, there would be a single “whizzy” button that says “Create Terrain”. However hope is too much in the world of ESRI and it has to be more complicated than that. Firstly you need to create a file geodatabase (in Catalog). Yes, thankfully ESRI have seen the error of their ways with personal geodatabases and finally have a format that is easily transportable and unlikely to corrupt. It can also store upto 1Tb per table which is handy. Once you have said geodatabase, you need to create a feature dataset inside it (note its a dataset, as in a collection of classes) and then put your terrain data inside the dataset. So if your LiDAR has come as a 3D shapefile then this needs to be exported into the feature dataset. Only then can you run the Terrain wizard to create your terrain (right click on the feature dataset, goto New and then Terrain). Note that the wizard does automate the terrain creation process and the individual tools are available in ArcToolBox. The 3D Analyst PDF does have some further info.