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Using RAW Export from PullSDTS
A project walkthrough by Bill Allen & Cecilia Ziemer
A project walkthrough by Bill Allen & Cecilia Ziemer
PullSDTS home [_Top_|_RAW Export_]
Note: The following techniques have been proven on Windows ME and Mac OS9, and should also work on Unix/Linux if suitable image editing software is available to the user.
Although it can be better to use the mesh representation of an SDTS DEM file, there are many situations when simple heightfield export can serve as well or better (perhaps faster or simpler) than mesh.
In Figure 1 at right is a Bryce 5 rendering by Cecilia Ziemer of a terrain created from a square grayscale TIFF file. That file was cropped from an image composited in Photoshop 5.0 from four "new SDTS" 10m DEMs exported as 8-bit RAW files from PullSDTS 2.0 beta 2b. (Where to get DEMs--digital elevation models.)
The results could be expected to be better yet if we could work from Pull's 16-bit RAW export (65,500+ grays vs. 254). Bryce 5 doesn't accept 16-bit grayscale files, and Photoshop 5.0 is very limited in what it will do with such files (e.g., it won't composite them). So this page will show everything done in 8-bit, but the steps would be very similar for 16-bit grayscale.
Because you are working with so few grays, you want to "equalize" (spread) them between the minimum and maximum elevations for the terrain you are after. This min/max might be for one or more DEMs in their entirety, or it might be for a particular terrain feature. If for one full DEM, you can simply click on Grays: Equalize to Self in the RAW File Export Settings dialog. In fact, using the [GIF Save] button may be all you need, exporting the already prepared equalized-to-self DEM preview. (Note that 10m DEM previews are reduced 33% to fit the same preview space as 30m DEMs.)
For DEMs to be composited later, perhaps in Photoshop, you need to use Grays: Equalize to Range, and type in the elevation Range: __ to __. To find the values to type in here, [Select] an SDTS DEM transfer DDF collection, or click on the [SDTS Report/Load] button, which is available whenever an SDTS transfer tarball or TAR has been selected. Jot down each DEM's elevation range and use their collective min/max.
In the example here, we were concentrating on a mountain with a base above 4,000 ft. and a peak elevation of 8,215 ft., which are the values you see used in Figure 2 at right. (The peak is Mt. Ellsworth in the Henry Mountains on the upper northwestern side of Lake Powell in southeastern Utah.)
RAW file export will be best (will have better "granularity") if you choose Units: Feet or Units: Decimeters. And you may find that Fill: White is easier to work with for compositing.
All RAW File Export Settings are preserved in Pull across sessions until you change them, so you only need set up your export once, then just load each DEM and export it in turn.
If you don't add a header to the RAW export file, Pull will offer a file name like TicabooMesa_1109x1392_PC.raw. This includes the quad name, its WxH pixel dimensions, and whether the file is in "PC" or "Mac format" (relevant only for 16-bit files). You need these details to complete the RAW import dialog, such as in Figure 3 in Photoshop 5.0 at right.
If you do use a header, be sure to give its size (128 bytes) to the receiving application's import dialog. The WxH and format details will be in the header, which a "hotshot" user can read by looking at the very top of the file's guts (in Notepad or by using a command line "type" command, etc.), but isn't something most people will want to do.
Figure 4 at left shows the four 10m DEM RAW 8-bit images placed in Photoshop as layers with gaps remaining between them. Note that the higher Mt. Hillers peak at top left is blown out to white, and the lower-elevations at the bottom are blown out to black, both as the result of equalizing to a range of just 4,000 to 8,215 ft. to get the maximum grayscale range for the mountain at the center of these four DEMs.
You can see in Figure 5 at right that these RAW files interlock perfectly, something that may not always be the case, especially if you are using pre-2001 "old SDTS" DEMs. If all the RAW files were exported from Pull with the same Equalize-to-Range setting, there should be no visible seam once the files have been butted up against each other. This is true even if the files are a mix of using decimal meters and feet for elevation--as these four files were. (Mixing whole meters with decimeters or feet might create a noticeable seam.)
Figure 6 at left shows a scaled-down lossy JPEG of the 855-pixel square TIFF that was cropped from the center of the composite of the four DEMs. You can download this 166Kb TIFF (use right-click on Windows, or click-and-hold on Mac, to save this file to disk). Try it yourself in Bryce or any other application that can work with 8-bit grayscale heightfields.
Cecilia Ziemer concludes this exercise by taking the Photoshop TIFF into Bryce 5: "I created a terrain and opened it in the Terrain Editor, hit New, and set the grid to 1024x1024. The TIFF was loaded into both windows under the Pictures tab (to prevent it from blending with white). There was no further editing of the terrain. I deleted the Bryce ground plane and chose Simple Black Background from Sky and Fog, and set ambient and shadows to about 50%. The material is an altered Sandstone (under Rocks & Stones) rescaled and filtered for Altitude in the Texture Source Editor. It was rendered at 1000x800 and that scaled down 50% in Photoshop to appear as you see in Figure 1 above."
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