New hillshading on OpenSnowMap.org

The relief (hillshading) layer on OpenSnowMap.org have been updated. On the major part of the world, resolution jumps to 30m instead of 90m beforehand,thanks to the ongoing release of 1 arc-second SRTM data by NASA.


To mak a long story short, the relief is more precise by a x1.5 zoom factor.

For more details, here are the data used on the serveur to generate the hillshading.

Screenshot from USGS explorer on Google-map background

30m SRTM data are used where available. Up north, data comes from the EU-DEM for scandinavia, ASTER for Alaska, Canada, Greenland and Russia. In an area extending from Greece to Iran, I had to kept the 90m SRTM data from CGIAR, I hope to be able to update this area soon (done).

To assemble those datasets, I use a script based on python-gdal to merge the data by small 1×1° tiles, filtering SRTM data by a 3×3 average filter and ASTER by a 10×10 filter to reduce noise. Gdal utilities then re-assemble everythingin a big Tiff. For rendering, I took the opportunity to pre-calculate smaller Tiffs at lower zooms to reduce the load on the tile server. The map should showup more fluidly.

Contour lines will be updated from the same datasets, if I can optimize them enough to fit my disks.

2 thoughts on “New hillshading on OpenSnowMap.org”

  1. Stefan:

    Hello Yves,

    \n

    thank you for your explanation, that will help others alot! But could you\nplease explain, where you got the 1 arc-second file from? Did you register at\nthe EarthExplorer or is there a way without registrating?

    \n

    Thank you for your great work!
    \nStefan

    Yves:

    Hi Stefan,

    \n

    Not sure I can give the full address here, however LP DAAC ftp address is\npublished here (works through http too):

    \n

    https://lpdaac.usgs.gov/about/news_archive/ftp_ip_address_change

    \n

    I use the dataset that can be found in /SRTM/SRTMGL1.003/

    \n

    Download the index.html, then make it a file list with a few-\nfind-and-replaces. Feel free to contact me via the website if you want the\ncomplete file list to pipe into wget.

    \n

    Please note that it takes **DAYS** to download the entire dataset.

    \n

    Cheers,

    \n

    Yves

  2. Gigls:

    Did you thing about releasing the toolchain as Open Source?

    \n

    I would really like to see some free contour line and hillshade datasets in\naddition to OSM data for a free map construction kit.

    Yves:

    Hi Sven,

    \n

    Thing is, the tool chain is already released and open-source:

    \n

    http://www.gdal.org/

    \n

    Now, for a kit, I’m afraid I can’t help. My actual work is here: \nhttps://github.com/yvecai/DEM-scripts/blob/master/2015/merge_dem_hs_and_contour.py.

    \n

    The script is currently running for contours which I didn’t even looked at\nseriously yet, it will likely run for weeks. As this kind of work needs such\ntime to complete on a reasonable hardware, people wanting to do so needs\npatience more than a ready-made solution, I guess.

    \n

    Also, as DEM source does not change a lot, if you are happy with my work, I\ncan simply give the resulting files. Send me a private message in that case.\nBut if you’d like a different result, you’ll have to experiment yourself. If I\ncan help, I’ll be glad to answer any questions.

    \n

    Please don’t see no mischief in the readme.txt of the above github repo.

    \n

    Cheers, Yves

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