Changes between Version 31 and Version 32 of Processing/SRTMDEMs
- Timestamp:
- Oct 12, 2011, 5:13:37 PM (13 years ago)
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Processing/SRTMDEMs
v31 v32 1 == Creating DEMs from ASTER or SRTM data == 2 3 '''** Note: The instructions below explain how to make an ASCII UTM DEM. If this DEM is intended for use with aplcorr, it will need to be a binary DEM instead. This is the same process but instead of r.out.ascii, use 'r.out.gdal format=ENVI type=Float32' from the lat long grass location. This will still need to be elevated to WGS84 and should be interpolated so there are no no-data values in the binary output **''' 1 = Creating DEMs from ASTER or SRTM data = 4 2 5 3 The ASTER GDEM is a global elevation dataset at 1-arc-second (30m) horizontal resolution, covering the earth from 83S-83N. More data about the dataset is available at http://www.ersdac.or.jp/GDEM/E/2.html, the dataset itself can be downloaded from http://www.gdem.aster.ersdac.or.jp/. … … 7 5 The Shuttle Radar Topography Mission mapped global elevations at a 3 arc second (90m posting) resolution between 60N and 56S. More information is available from http://srtm.usgs.gov/, and the data are available via the [http://earthexplorer.usgs.gov USGS Earth Explorer] 8 6 9 Both of these are relatively coarse for ARSF DEM usage but are sufficient in some cases. To create a DEM from these data: 7 == Obtaining the data == 10 8 11 1. Obtain data. ASTER should be used in preference to SRTM unless there is a good reason not to. 12 * ASTER from http://www.gdem.aster.ersdac.or.jp/. You will need to register, define the search area you're interested in and create an appropriate data order. 9 === Download from web === 10 11 * ASTER from http://www.gdem.aster.ersdac.or.jp/. You will need to register, define the search area you're interested in and create an appropriate data order. ASTER should be used in preference to SRTM unless there is a good reason not to. 13 12 14 13 * SRTM from http://earthexplorer.usgs.gov. Expand the "Digital Elevation" link on the left and tick the box labelled "SRTM". Enter bounding co-ordinates for the area you want data for, clicking the green "+" icon after each one. Note that this currently seems not to always work correctly for locations in DMS format (at least in Firefox), you may need to switch to decimal degrees (which work fine). Click on the "Search" button in the bottom-right, and you should be presented with a list of items matching your search (there should be only one thing in it). Click on the "SRTM" link (you may need to enable pop-ups if you've got them blocked), and you will be presented with a list of matching SRTM tiles and download links - download the data you want to use. Note that only SRTM 3-arc-second resolution data is available for sites outside North America. For sites in North America higher resolution data can be obtained via the USGS [http://seamless.usgs.gov/ Seamless Server] 15 14 16 2. The raw ASTER and SRTM data should be placed in ~arsf/ASTER and ~arsf/SRTM respectively (ARSF-DAN internal only - this isn't a requirement for use of azgcorr). 15 === Place files in repository and unzip === 17 16 18 3. Unzip the downloaded zip file. ASTER data will contain two GeoTIFFs (you want the "_dem" one) - the file name refers to the lat/lon of the bottom-left corner of the tile. For SRTM data, descend into the directory structure to find the file w001001.adf - this holds the actual data, though you can't move it without the rest of the directory structure. 17 The raw ASTER and SRTM data should be placed in ~arsf/ASTER and ~arsf/SRTM respectively (ARSF-DAN internal only - this isn't a requirement for use of azgcorr). 18 19 ASTER data will contain two GeoTIFFs (you want the "_dem" one) - the file name refers to the lat/lon of the bottom-left corner of the tile. For SRTM data, descend into the directory structure to find the file w001001.adf - this holds the actual data, though you can't move it without the rest of the directory structure. 19 20 20 21 If the ASTER data covers more than one tile, you will need to unzip lots of files - for convenience: … … 24 25 Each zipfile contains a file called Readme.pdf and piping yes into unzip lets us overwrite it each loop. 25 26 26 4. Fire up Grass. Select a location in lat/long projection using WGS84 datum (create one if none available), make a note of the selected location and mapset names. 27 == Creating DEM == 27 28 28 5. Import the data file. 29 === Scripted method === 30 31 Run asterdem.sh -a <aster_directory> -o <output_dem> 32 33 This will produce a lat-long binary DEM for use with aplcorr. If you want something else then you should use the manual method below. 34 35 === Manual method === 36 37 '''** Note: The instructions below explain how to make an ASCII UTM DEM. If this DEM is intended for use with aplcorr, it will need to be a binary DEM instead. This is the same process but instead of r.out.ascii, use 'r.out.gdal format=ENVI type=Float32' from the lat long grass location. This will still need to be elevated to WGS84 and should be interpolated so there are no no-data values in the binary output **''' 38 39 1. Fire up Grass. Select a location in lat/long projection using WGS84 datum (create one if none available), make a note of the selected location and mapset names. 40 41 2. Import the data file. 29 42 30 43 For ASTER data: … … 36 49 r.in.gdal input=w001001.adf output=<MAP_NAME> 37 50 }}} 38 39 '''Importing and patching multiple tiles'''40 51 41 52 If the data you have downloaded spans multiple tiles, then you will need to run the above but inside a for loop like so: … … 54 65 }}} 55 66 56 Once this is done, we need to stick all of the tifs together. First run 67 3. Patch tiles together 57 68 58 69 {{{ … … 83 94 Write down <MAP_NAME> somewhere - you will need it in a minute. 84 95 85 6. Quit Grass and then start it up again. Select a location using UTM projection for the target area or create one if none is available - make sure you've got the right UTM zone. Note you can also use whatever other projection you want, but this guide assumes you want UTM.96 4. Quit Grass and then start it up again. Select a location using UTM projection for the target area or create one if none is available - make sure you've got the right UTM zone. Note you can also use whatever other projection you want, but this guide assumes you want UTM. 86 97 87 98 Check [http://www.gpsinformation.org/utm-zones.gif] For the UTM zone 88 99 89 7. Move DEM to UTM location and set region. Here we can use the manual method of calculating the eastings/northings or simply grab them from the tile(s) we have input.100 5. Move DEM to UTM location and set region. Here we can use the manual method of calculating the eastings/northings or simply grab them from the tile(s) we have input. 90 101 91 '''Manual:''' 102 '''Calculate manually:''' 103 92 104 Use a conversion utility (eg see the spreadsheet at [http://www.uwgb.edu/dutchs/UsefulData/UTMFormulas.HTM#Spreadsheet http://www.uwgb.edu/dutchs/UsefulData/UTMFormulas.HTM#Spreadsheet]) to determine the boundaries of the target flight in meters within the selected UTM zone. If the flight spans two or more UTM zones, you will have to calculate the offsets appropriate to work out the east and west boundaries of the area. eg. If western boundary is zone 32 and eastern boundary is zone 33, for eastern value use zone 32, add 750000 to value from spreadsheet to find eastings relative to zone 32 bound. 93 105 … … 107 119 108 120 109 ''' Other method:'''121 '''Get from tiles:''' 110 122 111 123 - Set the northings/eastings to something very large e.g. … … 132 144 133 145 134 8. To elevate the SRTM/ASTER DEM to the WGS84 spheroid (as is required for LiDAR deliveries and LiDAR DEM patching) see [wiki:Processing/DEM2WGS84 Elevate an SRTM/ASTER DEM to the WGS84 spheroid].146 6. To elevate the SRTM/ASTER DEM to the WGS84 spheroid (as is required for LiDAR deliveries and LiDAR DEM patching) see [wiki:Processing/DEM2WGS84 Elevate an SRTM/ASTER DEM to the WGS84 spheroid]. 135 147 136 9. To output an ASCII DEM from the converted map, the instructions are the same as [wiki:Processing/NextMapDEMs those on the NextMap page]. Follow the instructions from about half-way down. Make sure to covert your DEM to an az-style header. '''If you want a dem for use by aplcorr then you need a binary dem - see the notes at the top of this page.'''148 7. To output an ASCII DEM from the converted map, the instructions are the same as [wiki:Processing/NextMapDEMs those on the NextMap page]. Follow the instructions from about half-way down. Make sure to covert your DEM to an az-style header. '''If you want a dem for use by aplcorr then you need a binary dem - see the notes at the top of this page.''' 137 149 138 10. When your DEM is finished, place it in ~arsf/dems and link it from within the individual projects. Make sure it's origin is contained in the file name e.g. <PROJECT_NAME>-ASTER.dem.150 8. When your DEM is finished, place it in ~arsf/dems and link it from within the individual projects. Make sure it's origin is contained in the file name e.g. <PROJECT_NAME>-ASTER.dem.