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.
Stefan:
Hello Yves,
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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?
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Thank you for your great work!
\nStefan
Yves:
Hi Stefan,
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Not sure I can give the full address here, however LP DAAC ftp address is\npublished here (works through http too):
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https://lpdaac.usgs.gov/about/news_archive/ftp_ip_address_change
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I use the dataset that can be found in /SRTM/SRTMGL1.003/
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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.
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Please note that it takes **DAYS** to download the entire dataset.
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Cheers,
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Yves
Gigls:
Did you thing about releasing the toolchain as Open Source?
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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,
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Thing is, the tool chain is already released and open-source:
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http://www.gdal.org/
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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.
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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.
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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.
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Please don’t see no mischief in the readme.txt of the above github repo.
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Cheers, Yves