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Thread: 30m DEM of the world for free

  1. #1
    Staff Sergeant ZeroG's Avatar
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    Exclamation 30m DEM of the world for free

    Hi guys! I found some entries on the board bout that kind of data, but somehow too dispersed..

    While looking for the best free DEM available on the net, I found an amazing alternative to SRTM (3 arc seconds = 90m resolution). Now you might say..wow..what news...he lives in the US..but NO!

    1. ALL THE WORLD
    2. FREE

    http://asterweb.jpl.nasa.gov/gdem-wist.asp

    It is a project called ASTER and produces 30m=1arc seconds GEOTIFF.

    I tried it with Globalmapper, exported and XYZ file for Visitor and...WOW....I CAN EVEN SEE RIVERS NOW!

    Just register there for free and get the detailed data!

    Take care!
    Last edited by ZeroG; Feb 18 2010 at 22:08.
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  3. #3
    CWR² Developer Bushlurker's Avatar
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    This is interesting!

    ASTER data has been around a while... I used the raw unprocessed stuff to derive false colour composites and DEMs of Cyprus for an Archaeo project back in 2001/2... the data was free then too - from the USGS EROS center in Sioux Falls...
    However - coverage was drastically incomplete - most datasets were still unprocessed... the procedure was - you selected the unprocessed data you were interested in - then either processed it yourself, or added a "request" that those particular tiles be moved to "priority" list... eventually, and I mean sometimes several months later! - you'd get an email saying your tile was ready and was lurking in the "finished" section... and you could go FTP it...
    Long winded, but FREE! - Good 'ol NASA!

    Not long after that I think they got completely overwhelmed with requests and/or ran out of funding - because the whole project became paying-customers/institutions only.....

    Now it seems - they're back in the public domain

    ZeroG's link should get anyone interested past the data browsing stage... I've just had a look - the interface hasn't changed... it's picky and primitive - but straightforward enough...

    A brief word about the ASTER array - though I advise anyone really interested to go Google - I'm operating from 10 yr old memory here...
    The ASTER satellite is a multi-array that captures data on a per-tile basis at a variety of resolutions and bandwidths... the raw result is a datablock that contains multiple layers... height info is derived from several of these layers via cunning processing - others are "Registered Radiences at the Sensor" - in various visible and non-visible bandwidths and resolutions... those are the raw datablocks we used to play with if there was no processed data available...
    If the tile you're interested in HAS been processed - and it looks now like they've pulled it together - all areas I've checked so far were OK - then you'll see a variety of datasets available for that focus area...
    GDEM V001 is the DEM, of course...
    L1B is the processed version of the visible and near-visible light "cameras"... NOT a visible light image like Google Earth, but surprisingly handy nonetheless...
    If I remember correctly there were several slices at various light frequencies...
    Different things reflect radiance at different frequencies...
    So certain things stand out like beacons at certain frequencies...

    Concrete is a classic example... crop plants are another, trees a third... different absorbtion levels means they stand out on certain layers of the data..

    It wasn't my department at the time, but we had an Aussie professor on that project who spent all his time doing "land cover" maps from the L1A/B data...
    He had all sorts of complex data processing software to do it right enough - ERDAS Imagine springs to mind... and some other software package I can't remember... last time I heard he was working for the Chinese... I'll see if I can get in touch with him and ask a bit further... I'm thinking the L1B might be a source of ezee vegetation data that could be used to make shapefiles for Rockets Maskmapper...
    I'll post again if I make any progress in that area...
    Meantime... I attempted to reregister for some test downloads - it wouldn't let me!... Turned out it was because I was already registered from years ago! hehe
    So it IS definitely the same system I used before...
    Slight fuss to retrieve my old log-in details and no problems after that... ordered data granules (tiles) covering Scotland - my main AOI and NOT available back in the early ASTER days... it's there now...
    Got a confirmation email and an FTP pull link within a couple of minutes... slowish d/l but files are fine... geotiff format - loaded into arcGIS no problems, so should be fine in other .geotiff capable programs...
    The "granules" are rectified, so they know where they are in the world, though they're in standard Geo lat/long, like GE and most large-scale stuff...
    Just reproject into UTM, WGS1984 datum and whatever zone the target terrain is in and it'll all look immediately more familiar...

    At first glance the data looks good... could well be a massive bonus here for the guys doing 1:1 maps, or anything close... over 1:3 or more you lose any advantage the more detailed data gives you by compressing back to 1px=90m or more anyway... Since my Scotland map is more like 1:9! it was probably the wrong data to d/l... I'll see if Iwo Jima is available... that's my side-project map and it IS 1:1...

    Anyway... enough for now... Well spotted ZeroG!!! I'd forgotten all about ASTER years ago... I suspect a few 1:1 maps may be getting a new DEM soon....!


    **edit** OK - having checked for Falklands Islands coverage with no success it seems that NASA may still not have processed all their data... I'm pretty sure the satellite itself gave complete global coverage - but I could be wrong, and it might be more like the SRTM coverage... either way - not every area will have data available it seems...

    B
    Last edited by Bushlurker; Feb 19 2010 at 06:00.

  4. #4
    Staff Sergeant ZeroG's Avatar
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    Uh, okay...than ALMOST all the world

    I've downloaded complete Germany last night (bout 2,2 GIGS) and realized that there was a relavtive small area which was not covered...

    Anyhow, we should be happy to have free data at THIS level of detail. I wont pay 30 Euros for 1 square kilometer at detail level 2m or 5m, as the cartographic institituitons of the federal states tend to demand...its the same with VBS2...just too expensive for private needs

    P.S. : B, you seem to have a REAL passion for your job
    Last edited by ZeroG; Feb 19 2010 at 07:30.

  5. #5
    Falklands data should now be available from the ASTER site, I ordered it yesterday afternoon and got it in the evening, so if should be available for anyone now.


    Planck

  6. #6
    data is not available from the ASTER site.

  7. #7
    Gunnery Sergeant
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    lol

    your first post was necroposting ... good luck!



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