Get Satellite Terrain Data into Terragen

We all know how many times we try and do something different in Terragen - rays, new textures, new camera angles, the only thing we struggle changing is the terrain - Trying to get features using those heavy-handed terrain tools is a nightmare, the mountains always look the same. Well, now they don't have to.

Welcome to the world of satellite data. Ever wanted to do a scene based on something like Mount St. Helens, how would you generate a terrain like that in Terragen? Get yourself off to the United States Geological Survey (USGS).

In this tutorial, I am going to show you two different methods of retrieving your data in the SDTS/DEM and GeoTiff-DEM formats. The GeoTiff DEM format will require you to download a free and small program called 3DEM, I recommend you also use this program for managing your SDTS/DEM format files too, but it isn't essential. I will reveal all in this tutorial. In addition, if you are downloading DEM files in the SDTS format, you will also need Winzip. All links are in the Questions and Answers part of this tutorial.

Before we get going, I think we had better bust through some of the jargon I will be using here.

What is a DEM file? A DEM (Digital Elevation Model) is digital representation of height data. DEM files come in different scales, for example, a 1:24,000 scale DEM (7.5 minute) represents a block of land 30 meters x 30 meters and a 1:250,000 scale DEM (also known as a 1-degree or a 3" DEM) has a resolution of 90 meters x 90 meters.The DEMS we will be handling here are the 1:24,000 type. If an individual DEM does not cover the entire area of interest, then multiple DEM files can be tiled together to make one large DEM by utilizing a 3rd party program like 3DEM.

What is a Quad? - For the purposes of this tutorial, Quads and DEM files (see above) are the same. The correct usage is to refer to the Quad as the area of data and the DEM as the data type, Quads can come in various different formats.

Can I get DEMS from any part of the world? Sadly not that easy. All DEMS are available for the United States in high detail, there is other data available for other parts of the world but it is extremely lacking in detail - You can write to your local government to obtain detailed information however. To make it easy on yourself, stick with the US files.

Is this the only way to get data? No, there are other methods of obtaining data - the methods shown here describe the easiest methods of obtaining data to your requirements. There are other web sites around, most of which will charge for data and also some Terragen sites which have limited DEMS already pre-converted to terrain files for you to download freely.

I want to learn more about DEMS, has anyone written anything on them? Yes, there is a text based tutorial written for the Terragen community here which explains in further details the various types of satellite data available (including for example MARS data), where to get them, and how to load them into Terragen.

I have two formats of DEM files?, one with a .DEM extension, the other is a collection of files, what is the difference? The two formats are both readable by 3DEM, the single file is in the US ASCII DEM format, the collection of files is in the SDTS format. Terragen can read the SDTS format directly via the firmament plugin.

Where can I download 3DEM? 3DEM is freeware and the latest version (15.6) available for download is here. NOTE: Earlier versions of 3DEM cannot read GeoTiff DEM Files correctly, please make sure you have the latest version.

Where can I download the Terragen firmament plugins? To enable Terragen to import DEM/SDTS files, you will need to download the firmament plugins from here.

Where can I download Winzip? The latest version of the popular decompression software is here.

Why can't I open TAR.GZ files in Winzip? In Winzip, Select Options>Configuration...>Miscellaneous from the menu and uncheck the box that says 'TAR file smart CR/LF conversion'. THIS BOX MUST NOT BE CHECKED

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The SDTS data is downloaded in small files, usually around 1Mb in size. These can be used individually, or combined to create a larger terrain. The web site used to obtain this information requires you to know the US State, the county and the Quad(DEM) name.

Finding the name of a Quad.

You can randomly select Quads for download, but if you know where your land feature is located, for example, Mount St. Helens is in the State of Washington in the county of Skamania (I found this out by doing a google search).

Knowing the location of your feature is not enough information however to obtain a quad file directly however, you need to know the name of the quad itself, I use a site which overlays the quads on top of standard US topology maps and is broken down into separate states - Digital Services When you load their page, select the State you need and from the choice of 3 PDF files, select the Quad Search (1:24k column), and an Adobe PDF file will be opened (There is a link to download the PDF viewer on this site) - this PDF file is around 1Mb in size (I recommend you save each one you open to your hard disk to speed up future searches) and will display a map. The states are coloured blue and the quad lines are in red. Each quad will be named here.

You will see from this image that the quad for Mount St. Helens is named "MOUNT SAINT HELENS" and you can also see the mountain itself occupies almost all the quad. If you downloaded the single quad for use in Terragen, you would find it extremely hard to get your camera far enough away to get an accurate enough representation of this wonderful peak.

The solution is to download the quads around this one too and combine them into one large terrain via the 3DEM program. The Quads I will download are "ELK ROCK", "SPIRIT LAKE WEST", "SPIRIT LAKE EAST", "GOAT MOUNTAIN", MOUNT SAINT HELENS" and "SMITH CREEK BUTTE". Notice also that the Quads for "Elk Rock" and "Goat Mountain" are in a different county, The county of Cowlitz.

Downloading DEM/SDTS data from the GIS Web site

The Geographic Information System(GIS) supplies its data in many formats, we are interested only in the DEM/SDTS format, Go straight to this page.

GIS DEM Download Page

The following map will be displayed, click on the State which has the data you need, in our case, it is Washington at the top left (WA).

The next screen to be displayed will be the County selection screen listing all available counties within the selected state.

For our terrain, we will be selecting six DEM files across two states, CowlitZ and Skamania. Select the county required (I selected Skamania first) You will then see another page listing out the individual Quads available for download.

On this screen, you can see the size of the download (for Mount Saint Helens it is 1.6Mb), the format confirmation - Make sure it says SDTS and should you want to have this delivered on a CD, the price. To download this quad, select the GREEN down arrow. (The brown one is for those who pay for a special fast link)

The last screen you will see (are we there yet? hehe) shows the filename itself. The link you need is the one ending .TAR.GZ (10 meter) Follow the on-screen instructions to save this to your disk. Repeat the process for the other five.

You will now have a file on your disk (or multiple) ending with TAR.GZ

Unzipping your data

The downloaded data is delivered in a compressed format to speed the download, you will need to make the use of a program to return this back to its uncompressed format, the preferred program is called winzip - check the Q&A at the top of the tutorial for details on how to get it and possible problems.

Locate your newly downloaded file and load it into winzip. These data files have been combined together using unix and need a two stage uncompress, winzip will ask you if you want to uncompress them to a temporary folder, select YES.

The files contained in the compressed data will now be displayed.

Extract all these files into one directory to create your SDTS DEM data. You have now successfully downloaded and stored your data, the following parts of this tutorial can be followed to enable you to get the most out of your SDTS data.

Using the 3DEM Program

Loading DEM/SDTS data directly into Terragen

Obtaining GeoTiff DEM Seamless Data

What do we mean by seamless data? Simply put, this means there are no joins. The USGS has provided a method of enabling you to specify your terrain area which may overlap Quads, counties, even States. To give an example, to download a reasonable sized terrain from the DEM/SDTS web site required us to download six quads because of the immense size of the Mount St. Helens Mountain. To obtain this via a seamless method, it means that you can specify your top left corner and your bottom right corner and the data will be delivered in one file with no combining needed. Sounds good? Well lets have a look at the web site.

I am aware that this may not work on all browsers but I have not found out why. If it doesn't work for you, let me know so I can try and find a solution to this.

 http://seamless.usgs.gov/start.htm

When the screen loads up, you will be presented with a screen similar to this snapshot.

On the left hand side, there is a toolbar which allows you to do various things such as zoom in and out, pan and select an area for downloading. On the right, there is, by default a list of layers which have been placed on the map, these will change depending on the level of detail being viewed and can range from roads, state lines, waterbodys and so on. There is a good help system provided with this, the button is at the top right of this screen and will explain all the elements of this screen well.

As I don't live in the US, I usually try and find out any interstate names and cities near to where my target data is, a decent enough place to help is www.mapquest.com. Other methods include a web search for your item of interest to find a local map of the area.

Once you have located your area of interest, zoom into the required area on the map by dragging a rectangle.

Once you feel you are within range of your target area, you should turn off the layer called NLCD (transparent) and ensure you have the Layers which start NED and the 1/3 NED. The 1/3 NED layer holds some very new data which is more accurate than the SDTS data - you can get an idea from the map below for what to look out for - Washington and Oregon are made up from the newer more detailed data and the more contrasted looking area where you see Montana and Idaho are built from data using the old type of NED data. If your feature crosses this boundary, you will be advised to use just the NED data, otherwise use the newer 1/3 NED data. When we get to downloading, you will see the differences in filesizes and appreciate how much more detail has been included.

On this screen, you will also see I have located Mount St Helens on the map and am zooming in by dragging an area, the red box indicates your selection.

NOTE: A word about how much you are allowed to download at any one time. The maximum filesize for FREE download is 100Mb, if you go over this amount, you will only have the option to purchase the data on a CD. If you do go over the max, simply go back and re-select a smaller area. The more you use this system, the better your understanding of how large an area you can select and if you are on a modem, perhaps how long each data chunk would take to download.

Once you are satisfied with your selection, select the rectangle on the download toolbar (at the bottom left), your selection box will turn green to indicate you are making a final selection.

Notice on this map I have the GIS names layer and roads Layer selected to help me find the target.

When you drag your area and release the mouse, a new window will appear indicating your order is being procesed, shortly followed by a screen similar to the one shown below

From this screen, you can see the difference between 1/3" NED data and the older format - I always try and get the 1/3 NED where possible. You will need to change the format of this Data from ArcGrid to Tiff format before continuing to download your data. Click the "Modify Data Request" button to do this.

For our purposes, we are only interested in NED data and can ignore all other product which may appear. Change the format to Tiff from the pulldown menus as shown in the screenshot and ensure the archive is set to ZIP. Click the "Save Changes" button to continue

Your order will now be amended to reflect the new changes, you may also find the size of the files have descreased as Tiff files are smaller than the equivalent ArcGrid format.

When you have made your changes to this data, simply click the download link of your required data item. Here I selected the 1.3" NED - Tiff Format.

As with SDTS data, you will be provided with a compressed file which can be uncompressed using winzip as described above. The file contents however will differ as shown here.

You will also notice the files have already had a subfolder allocated to them, remember that for when you try and locate your files in 3DEM. You have now successfully downloaded and stored your data, the following parts of this tutorial can be followed to enable you to get the most out of your Geo Tiff data.

Using the 3DEM Program

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Load up 3DEM and select "File"->"Load Terrain Model" from the top menu. The following dialog box will appear.

Select Geo Tiff DEM from the options available and click OK

Select the file you wish to read. Although the Tiff file format has miltiple files, the dialog box will only display the file with TIF as its extension, select that and click OK.

"3DEM will export Terragen terrain in widths up to 4096 by 4096 in support of Terragen version 0.8 and higher. 3DEM attempts to find the best match between the terrain matrix width chosen in 3DEM and the fixed widths allowed by Terragen (256, 512, 1024, etc). The rules for dimension matching are as follows:

DEM width less than 383 results in Terragen width of 256;
DEM width from 384 to 767 results in Terragen width of 512;
DEM width from 768 to 1535 results in Terragen width of 1024;
DEM width from 1536 to 3071 results in Terragen width of 2048;
DEM width greater than 3072 results in Terragen width of 4096.

To ensure the best reproduction of the terrain surface, it is advisable to select an area in 3DEM that matches the allowable Terragen widths. Press the “F8” key to activate readout of Matrix Width. Then as the size of the 3DEM outline rectangle is changed, the width of the terrain matrix to be converted to Terragen terrain is shown as “Matrix Width” at the bottom right of the overhead view window. If possible, this value should be matched to one of the allowable Terragen widths of 256, 512, 1024, 2048, or 4096.

Large terrain areas are always scaled down to provide Terragen a maximum terrain width of 10000 meters. This maximum size results in the best appearance of Terragen sky, clouds, and haze. Terrain altitude is scaled in proportion, resulting in a miniature Terragen terrain model that preserves all surface detail." - Extract from 3DEM Help File © Richard Horne Visualization Software.

This will create a single file ending in .DEM, repeat the process for all quads you wish to combine making sure you place them all in a single folder.

Once all six quads are saved, Select "File"-"Load Terrain Model" and select the USGS DEM model, click OK, and in the following dialog box, select all six quads (Hold down the [CTRL] key while selecting

The order of selection is not important as 3DEM will use the internal values to determine the physical location.

There are two ways of saving your models, Save the ENTIRE terrain, or if the terrain is simply too big, you can subset the area and save this smaller area.

To save the entire terrain, select "File"-"SaveTerragen Terrain"-"Entire Terrain" and specify the new filename and folder.

To make a subset of your terrain, drag the corner of the terrain to resize the black selection box, any other click will reposition it.

Press the [F8] key to get an on screen display of the size of the resulting Terrain matrix within the selected area. Even if you are using the unregistered version, you can export terrains larger than 513 and resize them in Terragen. This is the preferred option as you will get more details in your scene. I generally export larger than the intended size for this reason.

In the screenshot above, you can see I have resized the selection box so the resulting terrain will be 2715. Following the rules of 3DEM however (see above - Calculating how big a Terragen terrain file will be when exporting) the actual Terragen terrain will be 2049x2049.

I have also changed the lighting and colours of the terrain to suit my tastes. The colours have been changed and stored, when I load a new terrain, I recall these colours. The lighting by default doesn't pick up the height too well for me, so I also change the Azimuth value to Zero

Find these settings under "Color Scale"-"Shaded Relief"

When you are happy with your selected Terrain size, select "File"-"SaveTerragen Terrain"-Selected Area" and specify the new filename and folder.Back to Table of Contents

I have hinted that it is possible to import your downloaded DEM/SDTS Quads straight into Terragen without bothering with 3DEM. You must ensure you have installed the firmament plugin (see Questions and Answers) before attempting this.

NOTE TO UNREGISTERED USERS: I must recommend the 3DEM method and export the the entire terrain as a 1025x1025, load it into Terragen and resize it to 513x513. If you use this method, you will only be able to select a subset of this Terrain and forego some of the detail you could otherwise make use of.

Here is how to get that data in.

Start with a terrain size of 1025x1025 - Unregistered users - select 513x513.

Select the Firmament DEM/SDTS option in the Accessories menu.

For the unregistered user, the following screen indicates the area you are able to select

For the registered users, this is the same file with the larger selected area shown

When you have positioned the red square in a suitable position, click the "FI" button to import the data.

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