I was checking the import of USGS DEM's and followed the info in the manual, and unchecked the resize and center box in the options, but when I tried to import two adjacent 1:24000 scale DEM's they still ended up centred on top of eachother and not in their true geographic relationship. Is this a bug or am I missing something? I converted the new USGS SDTS files to the native ascii format for import to Vue4, and there is no loss of data, so I can't understand why it doesn't understand the positioning in the file. The manual mentions the terrain offset dialog box but I didn't see that come up. Also noticed that my Vue4 extras CD did not have any example DEM's as mentioned in the manual !! Is it a problem with using the 1:24000 DEM's and the fact they are in a UTM projection? Any ideas people :) I can still merge the DEM's other ways and create a true-height image, but I'm curious to know why the method in the manual failed for me. Lester

Forgot to say I'm using Vue4 version 4.02-02 if that is important :)

Have you ever heard of the program "3Dem"? it's a shareware program, which reads all of the typical and atypical types of DEM files. I cannot remember the URL, but a simpel search would turn it up, I'm sure. I have done very very little with DEM files, so am not one to offer any advice, but while experimenting with 3DEM with DEM files from the USGS, I found that Vue did import correctly, and in the "right place" the DEM files that 3Dem had converted. It seems as if that might be the key to proper DEM imports. Again, I know so little about it. DEM's are on my list of things to learn about, but I haven't really gone into it yet. :(

Attached Link: http://www.visualizationsoftware.com/3dem.html

Here, try this for 3 DEM, if you're interested....

Thanks for the info Mike. I tried out 3Dem and it is fast and works with both the old style USGS DEM's and the new standard of SDTS. It doesn't write USGS DEM format output, but you create a binary terrain matrix. I load that into Wilbur (did I put the link up for that!) and save the image out as a true-height field for Vue4. By the way, is there a limit to how big an image map can be used in Vue4?

To have two or more items import in relational positions, I believe they need to have been created (or exported) in those positions to begin with. In other words, if the DEMs you brought in weren't in next-to-each-other positions when they were created/exported, they'll import as individual objects instead of related objects. Hope that makes some sense okay. I'm not a DEM expert. (Where is Cheers when you need him?) I've used some rather large image maps up to 5000 x 5000. No problem, and I would suspect that they could be larger. It takes a little while for the material to load when you first apply it (or when you open a scene containing it), but there's no noticeable slowness after that initial bit. :)

That's an interesting point about the relative position of the DEMS. The test I did was with two "adjacent" DEM's which are 1:24K UTM USGS ones, and as such the edges are not square which may explain some things possibly! It did look like they were importing as individual objects. I think the larger-scale DEM's may be unprojected so they could provide a test too. It should be noted that the USGS DEM's (1:24000) issued prior to June 2001 had positional and other errors present, so make sure you get the latest ones from: http://www.gisdatadepot.com

Attached Link: http://www.big-i.com/tutorials/DEMs.html

Here's something else yopu might find interesting, at the link. It's a tutorial written about the "geographically correct" way of importing DEM's. The tutorial was written for Bryce 4, but the technique for Vue isn't different enough to matter. Well, the author, "Dig Real", who comes here occasionally, is really into DEM's and is now a Vue user as well. The site above, Big-I, also has alot of forums, and Laurie is the moderator of the Vue forum over there. It's pretty active, and Dig hangs out there mostly. He's been looking for people with interests in using DEM's with Vue. :)

I must say that no software beats Terragen for DEM's, they are always flat on the edges and you can merge dozens of them to create a huge terrain. WorldBuilder, Vue 4 and Bryce 5 all have problems with edges which is wierd since 3DEM/TG can do the job in no time and perfectly for so little money. Wilbur has a resolution/size limit no? Cheers!

As far as I know Wilbur does not have a size limitation, think it depends on how much memory it can grab from your machine. I have in the past got terrains with huge dimensions into wilbur! I had a look at the terrain editor, and it limits the terrain size to a maximum of 2048 x 2048! I can't find a way of increasing these values if I have a terrain with greater values to go in true-scale. Not sure how you could get a 5000 x 5000 pixel image map in without losing quality and true-scale Varian, but maybe there is a trick to it. I match the pixel size of the image map I load to the dimensions of the terrain I create in the terrain editor, which I assume is correct :) Lester

Hmmm...I used Wilbur in the past but not enough to notice the size limit, I was sure it was 256x256 but I might have been wrong. the beauty of Terragen is that you can load a 4096x4096 terrain from 3DEM...I wish we could have an export to Vue from within 3DEM then it wouldn't be a pain to import dozens of merged DEM's! :) Cheers!

Did someone mention my name? Mike, buddy, of course. :) (Mike, we need to talk.. ya really have to stop associating me with them damn dem files! ) J/K

Earlier this year, I became aware of all sorts of nasty stuff about DEM files, so when the USGS started a mailing list, I signed up pronto. Seems that there are 5 or 6 variations of SDTS DEMs. The variations are mostly errors and omissions in the data. If any of us in the 3d art community think we're fustrated trying to get DEMs to align, imagine how folks who make a living using em feel. They're not a happy group. Even more fustrated, must be the guys who try to write utilities for merging and converting DEMs.

The last word from the USGS, was that as of Oct 1, 2001.. all SDTS DEMs avail from them, would be of the same format, with all corrections in place. What's weird is I haven't heard any varification that this is now true. Folks on the email list are just as unhappy as ever.

With all that being said, I suspect that even perfect DEMs won't align in Vue. Only the position will be correct. As was already mentioned, the edges of adjoining DEMs can't align. From my experiments (I'm no expert.. nor a code writer), the way apps like 3DEM work, is by filling in the gaps between edges, maybe even an averaging thing. I tried doing that manually once.. thousands of polygons for each edge.. won't try THAT again! :) Anyway, 3DEM is easy to use for merging, and you won't see that seam in Vue, even if you place the camera right on it.

For anyone who just wants to convert an SDTS DEM to a standard ASCII one, SDTS2DEM is a great utility that has been updated to work with post Oct 1 SDTS DEM files. I can't find my link at the moment, but the 3DEM site Mike linked can probably lead you to it.

Hiya Dig! As I had said a while back, I tried your tutorial, and yes, I could not see any seams. I seem to also remember there were people at the Vue list at the time claiming there was no seam problem to begin with. shrug But I never was aware that the DEM format was so screwy to begin with. :P