Geotiff terrain vs Height multiplier question..

[yesmine]

I'm working with a new 1/9arc second terrain downloaded from the National Map Viewer site, then exported from Global Mapper as a Geotiff file.  I'm no Global Mapper expert, but following instructions all seemed to come out okay.  The GeoTiff height field was then imported into Terragen with "Flatten surface first" turned off, since I read in the forum that that was recommended, and so far so good.

What I'm trying to understand is why, rather than importing with a near-correct y-axis scale,  the vertical scale was off by quite a lot making mountains and peaks look like mile-high spires.

I knew it was only the height scale because the top-down view in 3D preview was fine..so the x and z scale was okay. Adjusting the "Height multiplier" amount and dropping it from 1 to about .04 gets the vertical scale to finally look about right, but I'm curious if anyone has an idea what may have caused it to not import with the y-axis defaulting to the correct height. Or is it normal to have to adjust the "Height multiplier" to get it down?

In either case, is there a way to determine what the true height multiplier should be as opposed to just guessing by appearance? Any other GeoTiff hints will be appreciated.
Thanks...

[heriosan]

I've been having the same issue, though it sounds inverted to yours. Importing a TER exported from GeoControl comes into Terragen very short, and I have to set the height multiplier to 2 or 2.5. A very curious thing...

[mash]

I tried a exporting a Geotiff from Global mapper and had the same problem with vertical scale but exporting as a DEM from Gloabal mapper file the data came into TG 3 OK and the scale matched a loaded 1/3rd arc second file.

I did try to load a 1/9 arc second file straight in to TG3 and the data came in with all the terrain stretching into the ground.

[yesmine]

Thanks to you both...I'm at least glad to know it isn't just me. I have typically used DEMs since some resolutions can be downloaded in that format. But at 1/9arc second, it comes in GridFloat or ArcGrid, which needed to be converted in Global Mapper. So I thought I'd try a GeoTiff thinking it might be a simpler way to go, and it does work though here we are. If I have time I'll experiment and see if there's something in the settings that corrects the y-axis stretching, but I'll stick to DEM for now.

It would be interesting, for future reference, to know whether GeoTiff's and DEM's have any different impact on the program or machine performance as far as RAM or rendering.
Thanks..

[Oshyan]

GeoTIFF and ArcGrid are both natively supported in Terragen 3, and the new 3.1 update that is now available improves some of the handling of it *when georeferenced*. In general I would recommend *not* converting or otherwise editing the original data. If you do need to convert/edit, do as little of it as possible and make absolutely certain that you're outputting with unmodified georefrencing info (this requires an application like GlobalMapper that is aware of such data).

If you're having problems with imported data, first try turning off Georeferencing and look at the terrain at at the 0,0 coordinate origin. If it's still "offset into the ground" or something, the next question is whether it's the original, unmodified data, or an adjusted version. If it's the original data, it may be a bug we need to look at and we'd want to look at the same data on our end.

- Oshyan