WorldBuilder Tutorials

DEM Tutorial

Four Ways to Convert USGS DEM Files for Use in AWB

USGS DEM files (DEM= "Digital Elevation Model" topographic files) allow you to recreate real-world landscapes in WorldBuilder (AWB). There are four types of DEMs which are commonly available, but AWB can directly import only two types, They are the 30-meter and 90-meter standard USGS DEM files (ASCII binary), which cover only the US. AWB does not yet directly support the SDTS DEM format or the GTOPO30 DEM format. The data from these last two formats can be used indirectly, however, as we'll see below.

Only a few 30-meter standard DEMs are available free off the Web, but 90-meter ASCII DEMs, SDTS DEMs and GTOPO DEMs can be downloaded for free. One great advantage of the SDTS format over the standard USGS DEM format is that the resolution is 9 times greater. This makes it possible to have landscapes with greater detail in AWB. The major advantage of GTOPOs is that they are about the only easy way to obtain landscape data covering the entire planet.

Using DEMs in AWB can range from 'easy' to 'complicated,' but the effort is well worth it. You can recreate and do close-up 'fly-throughs' of incredible real-world places like the Grand Canyon, Hawaiian Islands, Mount Etna, Nile River Delta, etc.

Below are several ways to convert these formats for use in AWB, each with its own advantages-disadvantages. The easiest method is listed first.

Standard DEMs come in mostly 10-meter, 30-meter and 90-meter resolution. The 10-meter and 30-meter DEMs are hard to find for free on the Web, but the 90-meter DEMs (with the lowest resolution) are readily available.

Advantages:

• Easiest to convert into AWB, using the standard Import feature. No conversion is necessary.

• New feature, called Isolines, can convert these standard DEMs to a skeleton-line-based landscape.

Disadvantages:

• AWB does not support the Skin feature on this type of landscape, meaning you can't change the resolution, use footprints, create erosion, or use evolution and roughness. Isolines offset this somewhat.

• Not easy if you need to use more than one DEM for your project.

NOTE: A few standard DEMs will be of poor quality -- that's just the way the USGS created them.

A) DOWNLOADING THE USGS STANDARD DEM FILES:

The higher resolution 30-meter standard DEMs are less common. There are some California 30-meter DEMs at:

ftp://130.166.124.228/ca_dems.2/clickable/overview.htm

Some very high resolution 10-meter DEMs of Washington State can be downloaded from:

http://wagda.lib.washington.edu/data/dem10m/

For the 90-meter topo data of the entire US, download the USGS files free from:

http://edcwww.cr.usgs.gov/glis/hyper/guide/1_dgr_demfig/index1m.html

a) For the 90-meter DEMs, use the USGS Online State-by-State Index to find your map.

b) Select the 'Uncompressed' rather than the 'Compressed' version. It is easier to use.

c) Download and rename the file from ***.gz to ***.dem. THIS IS VERY IMPORTANT, otherwise AWB will not recognize the file.

B) USING THE DEM IN AWB (THE FUN PART!)
a) Open a New Scene in AWB.

b) Select "FILE> IMPORT> USGS DEM" and locate your downloaded file. Make sure it has a ***.dem file extension. When you click on it, AWB will process it and ask if you want to "Place the LANDSCAPE in WORLD CENTER." Answer "YES" unless you have some reason not to do so.

c) The file will show up in the upper-right Object Tree as 'DEMSurface.' Unless you need to keep the old Landscape, just delete it. If you keep it, you need to hide it to keep it from rendering. You can work with the DEMSurface just like any other landscape and add textures, trees, etc. As mentioned, though, you cannot presently add erosion, or footprints, or change the default resolution. Pretty much everything else, though, works the same as a standard Landscape.

Advantages:

• Of the DEMs that must be converted, SDTS files are the easiest to use.

• After being converted, they are easy to place into AWB, using the standard Import feature.

• New feature, called Isolines, can convert these standard DEMs to a skeleton-line-based landscape.

Disadvantages:

• AWB does not support the Skin feature on this type of landscape, meaning you can not change the resolution, use footprints, create erosion, or use evolution and roughness. Isolines are able to offset this somewhat.

• Not easy if you need to use more than one DEM for your project.

NOTE: A few SDTS DEMs will be of poor quality -- that's just the way the USGS created them.

A) DOWNLOADING THE USGS SDTS FILES:
For the topographical data of the US, download an SDTS DEM file free from:
http://edcwww.cr.usgs.gov/doc/edchome/ndcdb/7_min_dem/states.html

Use the USGS Online State-by-State Index to find and download your map (note that only about 60% of the US is online). In theory, you can find an exact spot in the US, but it's tricky -- the USGS lists the maps only by name, usually named for some local feature, such as the name 'Bartlett Dam.' You have to know what you're looking for. The best way is to get a USGS hardcopy index from a local store that sells USGS topographical maps, or use latitude and longitude for your selected area.

B) UNZIP THE FILE:

a) The downloaded file will look something like this sample:
30_2_1_967620_tar

b) For backup, copy the file, and then select it in Windows Explorer with one click.

c) If there are any underscores (_), change them to dots (.). It should then look like this:
30.2.1.967620.tar

d) Sometimes, the file will download with the letters 'gz' after it. If so, remove them.

e) Under 'Options' in your zip program, the option for 'No CR/LF' should be unchecked. This is VERY IMPORTANT--otherwise, the file won't unzip correctly.

f) Double click the file to unzip it.

g) For SDTS DEMs, you will extract about 20 files that look like this: 1184CATD.DDF, 1184CEL0.DDF etc. These are the basic USGS files used to produce the landscape.

C) CONVERTING THE SDTS DEM TO A STANDARD DEM.
a) Download the sdts2dem.zip conversion program from the BLM site at:
ftp://ftp.blm.gov/pub/gis/sdts/dem/win95/

Unzip the file and check the readme.txt file if you want to know more about how to use it, but it's very easy. The following instructions are from the readme file:

b) Start SDTS2DEM by clicking on 'sdts2dem.exe' in Windows Explorer.

c) Click the "Select Input SDTS" button. Then find your directory of SDTS files. Once you have found the extracted files, click on any of the '*.DDF' files.

d) Click the "Select Output DEM" button. Select a directory and filename for the
converted output DEM. The program will automatically add a standard ".DEM" file extension.

e) Click the "Convert" button and within a few seconds, the selected SDTS files will be converted to a standard USGS ASCII DEM and stored with your output filename.

D) USING THE DEM IN AWB (Same as in METHOD 1).)

a) Open a New Scene in AWB.

b) Select "FILE/ IMPORT/ USGS DEM" and locate your downloaded file. Make sure it has a ***.dem file extension. When you click on it, AWB will process it and ask if you want to "Place the LANDSCAPE in WORLD CENTER." Answer "YES" unless you have some reason not to do so.

c) The file will show up in the upper-right Object Tree as 'DEMSurface.' Unless you need to keep the old Landscape, just delete it. If you keep it, you need to hide it to prevent it from rendering. You can work with the DEMSurface just like any other landscape and add textures, trees, etc. As mentioned, though, you cannot presently add erosion, or footprints, or change the default resolution. Pretty much everything else, though, works the same as a standard Landscape.

Advantages:

• You can use multiple DEMs joined together more-or-less seamlessly.

• Here you can use the 'Skin' feature on this type of landscape, meaning you can change resolution, use footprints, create erosion, and use evolution and roughness.

Disadvantages:

• Much more complicated with more steps to camplete.

• Final resolution is close to, but a little less than that with Method 1.

• Isolines won't work with this method, so you won't have any skeletons in your landscape unless you draw them in yourself.

A) DOWNLOADING THE USGS SDTS FILES:
The same as METHOD 1).

B) UNZIP THE FILE:
The same as METHOD 1).

C) PREPARING TO VIEW THE FILES.
a) The U.S. Navy has a highly useful free-download DEM-viewer available. Get the zip file from:
http://www.usna.edu/Users/oceano/pguth/website/microdem.htm

b) Unzip, install, and then open the program, which is called MicroDEM.

D) WORKING WITH THE FILES IN MicroDEM:
a) Select 'File/ New DEM' in MicroDEM. Find the directory with the extracted SDTS. Double click the first file, which in our sample would be '1181CATD.DDF.' MicroDEM will open and show you a top view of the landscape, usually gray reflectance (a sun-shaded view), though it might be the color view.

b) If you need multiple DEMs, start out by clicking the 'IN-OUT' button, then 'MERGE' and select your first DEM file. Just keep opening additional DEM files one-by-one. Make sure they are actually next to each other in the real world, and MicroDEM will join them all together somewhat seamlessly -- sometimes there are a few artifacts, but they rarely show in AWB.

E) CONVERTING THE FILES IN MicroDEM:
a) At this point, you can zoom in and check out the image for areas of interest to you, using the Magnifying Glass icon. VERY IMPORTANT: If you zoom in 2 times, for example, this translates into 2 times 2, or 4 times the file size. If you stay zoomed in, this file will be VERY large when you use it later in AWB. Undo the size increase by zooming back out when you are finished looking.

For a great 'almost-3D' perspective color view of the DEM, select 'MODIFY/ DISPLAY PARAMETERS/ REFLECTANCE' and then checkmark 'ELEVATION COLORS/ OK.'

b) When you are finished checking it out, get rid of the Grid pattern so it won't appear in AWB. Select 'MODIFY/ GRID/ SET GRID' and check the box for 'GRID/ NEITHER.' Also uncheck the box for 'MARGINAL INFO.'

c) If you are not already at the color view, then select the menu 'MODIFY', then 'DISPLAY PARAMETER' and then 'ELEVATION.' You'll see the false-colored view.

d) Select the menu 'MODIFY', then 'ELEVATION' and then 'GRAYSCALE.' You'll see a grayscale view (different from the reflectance) in which 256 shades of gray represent different Z-elevations, ranging from white as highest to black as lowest. In a minute, you'll use this grayscale to create a file for use in AWB.

e) Later in AWB, you'll need the elevation range for this DEM. From the top toolbar, select 'ANALYZE,' then 'ELEVATION HISTOGRAMS.' The top visible window will show you the 'RANGE' in meters. In our example, it is 455 to 1076 meters. Write this down to use later.

f) You'll need the image's X-Y scale later for AWB. Find the Grayscale image again on the desktop and click to bring it forward again. Select 'INFO' and write down the values at 'DEM POINTS ON MAP.' In our sample, it is 388 by 465. These are the X and Y coordinate values, with the X value listed first.

g) Select the menu 'FILE' and then 'SAVE IMAGE' to your hard drive.

h) Use Photoshop, or a similar program, to crop the image if you only want to use a smaller part of the total image. You can also crop it in MicroDEM if you want to go to the trouble of learning how to use the program. Then save it in your favorite format: jpg, tga, or bmp.

Note: If you crop and use less than the full grayscale, this will change the X, Y, and Z values. You can read the new X and Y in pixels under image size in Photoshop. You will just have to use your eye and guess at the approximate Z values later in AWB, but they will be within the limits of the range of Z-values that you obtained earlier.

If you use the full DEM image, it will be the same as the USGS paper map of the same name. It will cover about 7.5 minutes of latitude and longitude, or about 6-7 miles on each side (for the middle latitudes).

F) USING THE IMAGE IN AWB.
a) Open a New Scene.

b) In the Object Tree, select 'LANDSCAPE/ SKIN/ + / LANDSCAPE PICTURE PROFILE.' Use your elevation range from MicroDEM for the Min-Max values. In our example, it was 455 to 1076.

c) Choose 'SELECT AREA' if you want a higher resolution. You can raise the mesh count for the whole image, but that will add more rendering time. It is best to create a smaller area in Area Editor and then increase the mesh multiplier. Usually 2-3 times is enough for sufficient detail, without much loss of speed.

d) Hit 'PICTURE/ FILE/' and load the DEM image that you just created.

e) Select 'LANDSCAPE/ SCALE.' Change the X and Y settings to multiples of your image pixel size, like 388 x 465, or 3880 x 4650. X, or east-west, which is always the smaller figure.

f) Select 'LANDSCAPE/ SETTINGS' to set the POINTS. Usually 128, 256, or 512 is enough.

g) From 'SKIN,' add any modifiers that you want, like erosion, footprints, etc. Last, hit 'SKIN/ RESKIN' and have fun creating your new landscape.

METHOD 4) Converting a GTOPO30 for use as a LANDSCAPE PICTURE PROFILE:

Advantages:

• Can use multiple DEMs joined together seamlessly.

• You can use the 'Skin' feature on this type of landscape, meaning you can change resolution, use footprints, create erosion, and use evolution and roughness.

• The only easily accessible data of the entire planet.

Disadvantages:

• Much more complicated with more steps to do.

• GTOPOs have considerably less detail than SDTS DEMs -- about 140 times less. Only large features will show up.

• Isolines won't work with this method, so you won't have any skeletons in your landscape unless you draw them yourself.

A) DOWNLOADING THE GTOPO30 FILES:
For topo data of the whole world, get a GTOPO30 DEM file free from:
http://edcwww.cr.usgs.gov/landdaac/gtopo30/gtopo30.html

Use their site index to pick and download the map for the part of the world that you want.

B) UNZIP THE FILE:
a) Same as METHOD 1), except the downloaded file will look something like this sample: w180s60_tar.gz

b) For backup, copy the file, and then select it in Windows Explorer with one click.

c) If there are any underscores (_), change them to dots (.). It should look like this:
w180s60.tar.gz

d) Sometimes, the file will download with the letters 'gz' after it. If so, remove them.

e) Under 'Options' in your zip program, the option for 'No CR/LF' should be unchecked.

f) Double click the file to unzip it.

g) For GTOPO DEMs, you will extract about 8 files that look like this: w180s60.dem, w180s60.hdr, and w180s60.gif, etc. These are the basic data files used to produce the landscape. The GIF file is a low-resolution image of the area.

C) PREPARING TO VIEW THE FILES.
The same as METHOD 3).

D) CONVERTING THE FILES IN MicroDEM:
The same as METHOD 3).

E) USING THE IMAGE IN AWB.
The same as METHOD 3).

Happy Landscaping, and if you have any problems, contact me.

Allen Whitt