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12

This seems like a good place to describe a simple, fast, and more than reasonably accurate way to compute slopes for a globally extensive DEM. Principles Recall that the slope of a surface at a point is essentially the largest ratio of "rise" to "run" encountered at all possible bearings from that point. The issue is that when a projection has scale ...


12

Update: I think wget would be better, i just don't use it very often: wget -r -A.zip http://dds.cr.usgs.gov/srtm/version2_1/SRTM3/ Also see for some retrieval wait options (if you want to be courteous): http://superuser.com/questions/178297/wget-terminates-unexpectedly/178326#178326 You could curl the files with a little bit of text editor work. For ...


10

I'm guessing the horizontal units for your raster are in either degrees or arcseconds. You need to reproject this raster to a spatial projection where your horizontal and vertical units are the same (i.e., if the vertical units are in metres, then I suggest using UTM, which has horizontal units of metres). To reproject a raster with ArcCatalog/ArcGIS, look ...


9

For a local solution, GRASS can be scripted to do this: # extract raster values at our points # use cubic convolution for interpolation between DEM locations v.drape in=my_pts out=pts_srtm_elev type=point rast=srtm_dem method=cubic I ran an extended version of this for one of my use cases and performance of v.drape was no issue at all.


8

Data format I'll take it as a little exercise in how to program a data reader. Have a look at the documentation: SRTM data are distributed in two levels: SRTM1 (for the U.S. and its territories and possessions) with data sampled at one arc-second intervals in latitude and longitude, and SRTM3 (for the world) sampled at three arc-seconds. Data are ...


7

Download the source code from here http://www.osola.org.uk/elevations/index.htm SRTMGeoTIFFReader.php is the clever file the reads the GeoTiff and converts the elevation values (in meters) into Lat/Lng coordinates. I doubt this is exactly what you want but it does give you a solid base on understanding the process required to accomplish the task from your ...


6

Mike Migurski (of Stamen Design) recently made a major new open terrain map: details on his blog and I put up a quick map viewer for it. It does terrain relief shading with various DEM sources combined with roads, labels, etc from OpenStreetMap. The source code to generate the map is on GitHub.


6

TopOSM has terrain tiles - though limited coverage (US Only) http://www.toposm.com/us/ Full Details http://wiki.openstreetmap.org/wiki/TopOSM All the Rendering and Source files are available http://svn.openstreetmap.org/applications/rendering/toposm/ License is the same as Open Street Map OpenStreetMap Data is available under the Creative Commons ...


6

This is a fairly common problem to run into. My guess is that your SRTM data are still in geographical coordinates and has not been reprojected. As such, the elevation units are being measured in metres while the xy-units are in degrees. You need to use the z-conversion factor to convert the xy-units and z-units so that they are the same. The common approach ...


5

You can generate your own using Maperitive: generate-relief-igor command generate-tiles command A sample hiking map using such tiles.


5

A few thoughts: A previous answer correctly recommends resampling during display to smooth out the irregularities in the hillshade. This is primarily used for cartographic effect when you are finishing a map. Use the Image Analysis window to run a 5x5 smoothing window over the image Find better elevation data. 10 m NED Data is available for the ...


5

SRTM (Shuttle Radar Topography Mission) was a shuttle mission, no satellite involved. But essentially the satellites do not cross the poles. In a geosynchronous orbit, which most imaging satellites are in, you get a pattern like: This is great because it means that the orbit can be timed and most parts of the Earth get covered at around noon, getting ...


4

http://dds.cr.usgs.gov/srtm/version2_1/Documentation/Continent_def.gif You can use http://www.latlontoelevation.com/ lat/lng to get the Shuttle Radar Topography Mission (SRTM) data too.


4

gpsvisualizer.com will do this for you. I believe it is using GPSBabel and Google API in the background.


4

SRTM data is easy to download for a given area, I've use this site in the past. The files aren't huge, and you can get them as georeferenced TIFFs. Downloading the whole world might take a while, but a couple of tiles covers a pretty large area. The issue you might have is with horizontal resolution, which is about 90 metres for most of the world, and the ...


4

When you downloaded the data what format did it come in? By definition, if the data is a raster format, it can be considered 3D data, as it has a x,y,z value. If you are looking to have it extruded in ArcScene then you will want to do a few of the following things. Assuming your data is in a usable raster format (ie: GeoTiff) then you will want to do the ...


4

The interpolation modules in GRASS can work with a line vector, such as contour lines, to create a DEM raster. So you could create a DEM raster from your contour lines, then "correct" the ASTER GDEM with this data. The catch will be in matching elevations from the contour-based raster to the ASTER GDEM, to avoid a terrace effect at the edge. The procedure ...


4

We had good results with this approach: Convert original raster DEM (90 meters) to points Interpolate points to a new raster (finer resolution e.g. 10 meters) Create hillshade from new raster (step 2). It was a few years ago - so I can not remember the parameters exactly. But I guess we used a spline interpolation. Spline produced very soft surfaces. ...


4

I suppose that it is the result of r.shaded.relief. Have you set the correct resolution of your region of work (resolution of the SRTM layer, Res: 59.74514451 here) ? Resolution of the SRTM layer: Resolution of the region: Elevation; r.shaded.relief without grainy surface with the correct resolution


4

You might try the USGS SRTM FTP site. I can assure you that each of the tiles you list as examples are there in their proper .hgt format and there are no suspicious files in the associated zip file. And here is the tile S35E147, buffered with the surrounding eight tiles as well:


3

Simply put, there isn't one. By definition a coordinate system based on degrees is un-projected. In common parlance we say WGS84 is a "geographic" projection, but that's untrue, just for convenience. I think I remember reading about a software or process for accurately working with elevation models in un-projected geographic space but I can't locate it ...


3

It sounds like you need this as a generic solution, i.e. having all the world's elevation data available to you for any track you want to process, hence not wanting to store all the CGIAR data locally; the gpsvisualizer.com mentioned above (@Llaves) may be your best bet. If you don't need high resolution, the GTOPO data set (1km grid) is only ~300MB for the ...


3

The folks at telascience are starting to revive the OpenAerialMap.org project which is on hold for now. They have already processed NAIP which can be found at http://hyperquad.telascience.org/naip/ They also have world coverage of Landsat done. As far as contours, elevation, shaded relief, etc, part of the plan is to include SRTM http://srtm.csi.cgiar.org/ ...


3

You can also query with r.what or export the map to an ASCII matrix with r.out.ascii.


3

The length of the arrows is determined by the magnitude_map (which would usually be the slope). If you want the arrows to be of uniform length, you can just create a new map of ones (r.mapcalc ones=1) and use that as the magnitude map. You can then control the length of the arrows using the scale factor: d.rast.arrow map=aspectMap skip=50 magnitude_map=ones ...


3

You can use Maperitive to download SRTM tiles automatically and unzip them. Just zoom in/out to the area of your interest and it will download all the required tiles to your disk. And best of all, it's free. Here's a sample hillshading + hypsometric rendering generated using SRTM tiles in Maperitive:


3

FTP site ftp.glcf.umiacs.umd.edu Folder /glcf/SRTM I use Filezilla - fast and efficient


3

Here's what the original NASA's SRTM document says (emphasis is mine): File names refer to the latitude and longitude of the lower left corner of the tile - e.g. N37W105 has its lower left corner at 37 degrees north latitude and 105 degrees west longitude. To be more exact, these coordinates refer to the geometric center of the lower left pixel, ...


3

The "Marmota" project at FBK, Trento, Italy, is offering the functionality you seem to aim for: http://tev.fbk.eu/marmota/ There are a series of publications available on that site. Furthermore, see the related question here.


3

I would create a virtual raster with both images. You can do it in Raster > Miscelaneous > Build Virtual Raster (Catalog). It will be a quite small file that will allow you to open both images at the same time in QGIS, and set blending to them globally. That way the overlapping blending mode or transparencies won't show. Two overlapping images with ...



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