How do i Use DEM Data and how it is affecting the Landscape?

Started by PeterParker, February 09, 2014, 07:22:45 AM

Previous topic - Next topic

Oshyan

Georeferencing only means the terrain is positioned at the correct place on the planet, without it the terrain is still "on the surface", it just shows up at the 0,0 coordinate origin.

The demo was done with Terragen 3.1 (not yet released, coming later in February) that has some improvements for working with DEM data when georeferenced and far away from the coordinate origin. Until the release of 3.1 it may be advisable to avoid Georeferencing unless you're certain you need it. Keep in mind that the primary benefit of georeferencing will be for real-world projects *that require a correct planetary context*, or for situations where you're trying to align multiple adjacent or overlapping DEMs. If you are only loading a single DEM tile and don't intend to ever view it from a planetary context, there's really no point in using georeferencing.

Richard, if you're aiming for real-world scales (terrain area as well as height), then you shouldn't ever need any heightfield modifiers on a georeferenced terrain. If you're not using georeferencing then you might. If you're having issues with incorrect scales when georeferenced, that's probably a bug and something for which we'd need some example files to look into it.

Last but not least, the National Map Viewer above is by far the best resource, both in terms of functionality/flexibility, and in my opinion in terms of ease of use for getting specific areas. Some places have data that is "easy" in that you just click a square and it downloads the data directly, but they lack the flexibility and modern data that the National Map Viewer has. So I'd strongly recommend figuring out whatever problems you might be having with that site and get it working, then learn to use it (it's fairly simple) as it really is the best option at present. Try finding 1/9 arc second NED data in easily usable form elsewhere...

- Oshyan

Matt

You can use Georeferenced DEMs in 3.0, with the georeference checkbox checked, but you should adjust the coordinate system in Terragen so that the DEMs are centred at the top of the planet. If you go to the Planet node (usually this is the node named "Planet 01"), you'll see there is a parameter called "Lat long at apex". This defaults to 0,0. Different values cause different parts of the georeferenced world to be placed at the top (the 'apex') of the Terragen planet.

Here are the steps to do this:

1) Go to the Geog Heightfield Load node (the one that loads the DEM data and has the "georeference" checkbox). Copy one set of lat-long coordinates (for example, "NW corner lat long") using the button with the clipboard icon.

2) Go to the Planet node and paste the coordinates into the planet's "Lat long at apex" parameter using the clipboard button.

That's it. You only need to do that once with one of your heightfields. If you have multiple heightfields nearby that are all georeferenced, they should line up correctly with the first heightfield, with one corner of the first heightfield being placed at the apex of the planet.

Terragen 3.1 will work better with heightfields placed further away from the apex of the planet, but I would still recommend doing this in 3.1 because there are many reasons why it's better to work near the origin (which is the apex of the planet if you don't move or resize the planet).

Matt
Just because milk is white doesn't mean that clouds are made of milk.

PeterParker