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 Post subject: SRTM height data
PostPosted: Fri Jan 15, 2010 12:07 am 
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Joined: Thu Jan 14, 2010 11:59 pm
Posts: 1
I would dearly love to be able to directly import NASA SRTM (Shuttle Radar Topograpy Mission) height data directly.


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 Post subject: Re: SRTM height data
PostPosted: Sun Jan 17, 2010 10:56 pm 
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Programmierdochfix
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Joined: Tue Apr 27, 2004 12:53 pm
Posts: 892
Location: Braunschweig
Hi and welcome.

SRTM .hgt files are simple raw files. I managed to import them. I only have a few problems with the resolution until. Compared to the resolution of PnP the SRTM resolution of 30 and 90 meters is very poor. But I'll release an importer update for this very soon.


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 Post subject: Re: SRTM height data
PostPosted: Thu Jan 21, 2010 10:02 am 
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Programmierdochfix
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Joined: Tue Apr 27, 2004 12:53 pm
Posts: 892
Location: Braunschweig
Well... I have an updated version of the RAW import plugin which is capable of loading .hgt files.
It's not yet very comfortable, but at least it works.

Please extract the following file to the PlugIns directory.
Attachment:
PnPTCRAWHMapImportPlugIn.zip [96.17 KiB]
Downloaded 417 times


Now please start the whole terrain import from the overview map and select the "Heightmap import from RAW" plugin from the "Heightmap importers" group.

In the following open file dialog first select "All files (*.*)" in the file type drop down box, so you are able to select a .hgt file for import.

Use the following settings for the import:
Attachment:
hgt_import_settings.png [7.18 KiB]
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Important: PnPTC cannot import height values < 0! The .hgt format uses signed values. So heights below zero are possible. Zero height in .hgt format is the global water level. So if you are going to import coast regions or regions with height below the global water level, you have to offset the height. Example: You are importing a cost and the lowest value of the terrain is -200 meters (so 200 meters below the water surface). Then you have to use at least a value of 200 for the "Height offset" parameter in the settings dialog.

Next there is the really difficult part: How to match the .hgt file to the terrain surface of PnPTC. The available world-wide data set of .hgt files has a resolution of 90 meters. Only for north america data sets with a resolution of 30 meters exist. But this is still a very poor resolution compared to the resolution used within PnPTC. You can set the resolution in the "Terrain Properties" dialog (parameter "Detail element size"). But the maximum value there is 10 meters. So you cannot go down to the resolution of .hgt. Therefore you have to scale the data source which can be done within the last dialog ("Select import area") of the import procedure. You should limit the import area of the data source to the area available in PnPTC so that it will result into the correct metrical units. Please see the manual section 13.2 on page 72.

The last step is a point which will be optimized/simplified in the future in a specialized .hgt importer PlugIn. If you need some help obtaining the correct settings, please let me know.


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