Now you are ready to jump over to the Geocomm website and start the download process.

* Click the GIS Data tab across the top of the page.

* Click the Download GIS Data button.




* Click the Washington State image on the U.S. map.





* Click the Pierce County link.



* Click the 24K DEM link.


This next page is where you will find the quad names to download. Search the list and you will come to our first quad, Golden Lakes.


On the right side you will see two download links. A green one and a tan one. The green one is the free download, and the tan one is for the premium download accounts. The only difference is download speed. You also have the option to add them to the cart and purchase them on CD via the mail. However you get the files is completely up to you. I will be using the free method for this tutorial. Once you get to the download page you may have two options. The 10 meter and 30 meter image. This has to do with resolution of the image. The lower the number the finer the detail and better overall quality. For this tutorial we will be using 10 meter DEM data for all quads. Sometimes you will only have the 30 meter option. Always opt for the best quality possible, for obvious reason. There may also be cases where you have all 10 meter DEMs for most of your location but one quad will only have 30 meter available. That's a judgment call on your part. I've mixed and matched resolutions before and just made sure to keep that area out of the focal point of the rendered frame. It looked fine for the shot I was doing...again, your call.

For clarification issues I tend to rename the files being downloaded. As you can see in this case the default name does not represent something logical that we can distinguish quickly.



I would append the file name to be something like:

* "GoldenLakes - 1675707.DEM.SDTS.TAR.GZ"

Again, this is just me but I find with all the organization that will be needed in later steps it helps to keep quad names straight. Go ahead and repeat this process for downloading all 15 quads shown in this image.




Now that you have all of your DEMs downloaded you can extract the files. The *.gz file format is simply a compressed file that WinZip or WinRar should be able to extract with no problem. When extracting the files I tend to use the "Extract To" method and accept the default sub folder name. This is why you want to append the quad name to the beginning of the files when you are downloading them. That way you are left with a subfolder structure that is easily recognizable when browsing your project. When you extract the file you should have about 18 *.ddf files and a README for each quad.

NOTE: Occasionally I've ran into an issue where I download the quad *.gz file and when I extract it there is only one file inside. I have not yet figured out what causes this, but usually re-downloading and extracting the file again will fix it. You may need to try downloading from a different machine. That's usually what I do.

Now you are ready to start converting all of these files to something that Photoshop can read. For this we will be using a program called PullSDTS. In order to use this program you must have the Python plug-in installed on your machine. Launch PullSDTS and click the [Select File] button.


Locate the first quad folder and you will note that only one *.ddf file is listed. Select and load that file. Now click the [Copy] button to copy the header text to the clipboard.


Launch a text editor like notepad and paste the text into the new document. Repeat this process of copying and pasting the headers into this new document. This header information makes up what will be our rangeStatistics used in the conversion process. Information such as elevation, quad size, and world coordinates are in this file. I've attached a copy of my completed text file rangeStatistics.zip for you to download. What you need to do is scan through all 15 headers and determine what the lowest (min) elevation is and the highest (max) elevation for our entire range. You also will need to figure out what the Northwest and Southeast coordinates are for later. We will use the east and west coordinates to determine how wide our range is, too. I've done this for you in the text file and added this to the top of our rangeStatistics file. After you get all of this required information, it's now time to convert the data. Go back into PullSDTS and click the [Select File] button again. Re-load our first quad, then click the [Load DEM] button. You will now see a greyscale image of that quad in the left side window. Click the [Save RAW] button.