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USGS Elevation Data

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I was looking for some real-world elevation data and I found this sample from the USGS National Elevation Dataset (I''m using the 2-arc second integer file.) Supposedly this data has a resolution of 60m (2-arc seconds). So I dropped this into an old heightmap renderer of mine, and as you can see, something is not right here (this should be to scale): I tried scaling down the height values by about 1/50, resulting in this (note: this is not from the same spot as in the previous shot): This sample is of St. Louis, but I tried samples from other geographic locations, and they all have this same "terraced" look. Any ideas on what I am doing wrong? I don''t really think either of these screenshots look at all reasonable for 60m-resolution elevation data.

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Eric, I have some USGS data of Death Valley, California. The map encompasses a valley floor with an elevation 282 feet below sea level and an escarpment rising over 11,000 feet in elevation. It is a MUCH better set of data for testing heightmap algorithms. St. Louis is not exactly known for its mountainous terrain.

Your problem likely results from over scaling of the data and a limited resolution in the dataset. Even my Death Vallye data has this, but is virtually not noticable because the terraces are miniscule compared to the mountainous relief.

If you would like, I can email you the data, which I have reorganized into a very simple file of integers. I can provide you the source code to read the data too: about 10 lines of code.

I would like to see how your algorithm displays the data. Also, I may have a solution to completely eliminate the terraces.

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bishop_pass, your Death Valley data sounds great -- I would love to have a look at it. My email is eundersan@mail.utexas.edu.

Regarding these screenshots, they are from the track editor of a game I worked on a while back, called Hover. Each grid point is simply assigned the "sand" or "dirt" texture based on its slope. There was also a static LOD algorithm that reduced triangle density on flatter areas, but this was only used in-game.

Anyway I''m only using it now to experiment with real-world elevation data. I hope to find some good terrain for my next project, a downhill racing game.

Now for another picture, this time of Ranger Peak, WY. The data is from Charttiff.com -- they let you buy individual DEM "quads" for one dollar. The Ranger Peak quad is about 235x340, and I''d say about 200x200 of it is in view here. I scaled the height 1.5x.

Needless to say, this turned out a lot better than the USGS sample data. Charttiff apparently "cleans up" their original data, so I wonder how much of this is just algorithmic... regardless, I think it looks pretty good/natural.

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Cool!

I wish I could show you my screenshots of the same data, but I have since thrashed the code with modifications and that was a long time ago so I can''t easily get it back to working correctly.

If you want to see something kind of cool, I would turn the fog off, and pull the camera back enough to get the whole height map in the frame. And you might want to tone the scale of the altitude down a little. Try about 1/3 of what you are currently using.

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Sure...

Here''s your Death Valley map again, maybe more what you had in mind:


I liked this Death Valley terrain so I found some more. Here is Fall Canyon, from Charttiff.com:


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Eric,
I have a couple comments. What you are doing is cool, and I would imagine you are having fun with it. I notice that you have created an algorithm that selects whether to render sand or dirt. Although you argued against me (only a little though) in my Snow on terrain? thread, I think that thread (at least what I was proposing) was in the same spirit as your sand vs. dirt algorithm. Essentially, it proposes a preprocess of the terrain to identify those areas which would have snow cover, and contrary to many of the people who posted in that thread, the whole concept was not that complex. In my last few posts in that thread, which are very recent, I provided an equation to figure out the snow coverage. Bottomline: even Death Valley gets snow in it''s higher elevations! If you are interested, I could help you implement the snow calculations and we could see how they would look on your data sets.

I have some more data sets for you in the same format I gave you Death Valley in. I just have to find them. One is Owens Valley, which is about 100 miles northwest of from Death Valley and is actually considered a deeper valley (one of the deepest) because it has 14,000 mountain ranges rising in escarpments 10,000 feet above the valley floor on both sides of the valley. I think I have the Grand Canyon floating around on my hard drive also.

Fall Canyon! Is that the Fall Canyon in Death Valley? I hiked up that canyon about a year and a half ago. It becomes a slot canyon the further in you go.

Another useful calculation to run on the terrain as a preprocess is the contributing area function. It is a really simple function (about 5 lines) but it is really powerful. It will tell you the amount of water which flows through a cell, and you can use this data to determine the locations of rivers, creeks, streams, and areas of increased vegetation.

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Ah yes, I saw the Snow on terrain thread again when this forum was running "bishop_pass'' Greatest Hits" just recently

Regarding more complex calculations for snow cover or vegetation, I agree that they would be merited and I appreciate your willingness to help on this. However, it''s going to be a while before I begin work on the terrain engine for my current game. At this early stage I just wanted to determine the availability/viability of real-world elevation data (As I mentioned before, the terrain engine that rendered these scenes is from a previous game of mine).

Anyway, when I do eventually get back to the terrain, I will post some screenshots in this forum, and I look forward to feedback from you and everyone else

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