Target
Refer to Downloading Digital Elevation Data (SRTM) from USGS EarthExplorer - YouTube to learn to download real-world height map data from USGS. And try to import Houdini.
USGS：https://earthexplorer.usgs.gov/
0. Register an account and log in
If you don't have an account yet, you need to register an account here and confirm the email.
Then log in.
1. Define the area
First, define an area. (Note: This area is not the area of the last downloaded terrain height map data, because the last downloaded height map is segmented, and this area only indicates in which area to search for map blocks)
Open the USGS official website , and delineate the area in the first column on the left "Search Criteria".
Click with the left mouse button to draw an area in the clockwise direction.
2. Select Data Set
Click on the second tab "Data Sets".
The meaning of Data Set is currently unknown.
This is just to get the height field data, so I chose the same as the tutorial :
3. Download data
Click the Results button (or select "Results" in the page)
and wait for the data to load. . .
Once loaded, you can see the map tile data on the left. You can click the little foot icon to display its corresponding location:
Click to download
and select the format. I don't know these formats at present, so I chose the same as the tutorial
: after downloading, I get a picture in .tif format:
4. Import Houdini
Use the HeightField File node in Houdini to load tif images.
Initially, it should be flat. This is normal, after all, did not tell him the unit.
So the question is, what is the length and width represented by this tif image, and what height does its value correspond to?
Let me talk about the conclusion first. If you don't require special precision, you can:
- Size is set to 111
- Height Scale is set to 30
Effect:
The two values here are derived as follows:
5*. Determine the size of the data
First of all, for the plane direction:
you can view the information of the data:
you can know that its length and width are 1 longitude and 1 latitude.
- For latitude, it is about 111km
- For longitude, the equatorial part is about 111km and gets smaller the farther you go from the equator. This is also roughly regarded as 111km. (Actually, you need to multiply cos (latitude))
For the vertical direction:
I suspect that there is information about the real height corresponding to its value in the tif file format, but it is not visible in Houdini. But it is visible using QGIS . For example, if I load this picture, I can see that
the value in the tif picture can use the calculation range function of the HeightField Remap node:
in this way, you can know that the maximum value in the picture is 0.159823, which corresponds to the real height of 4891 meters.
So, the scaling is 4891/0.159823. It is about 30km. (I also tried another plot with a zoom value of about 30km as well)