[mapserver-users] Hello from Finland

[Rahkonen Jukka (MML)]

Hi,

-----Alkuperäinen viesti-----
Stefan Gofferje wrote:

> Terve Jukka,

> On 3/16/21 12:54 PM, Rahkonen Jukka (MML) wrote:
>> When it comes to memory usage with raster files, Mapserver is reading rasters with GDAL so in this case with https://gdal.org/drivers/raster/grib.html. I have never been playing with GRIB files and I do not know how well the format is optimized for features that are needed for making fast map services: fast access to subregions and overview levels. I have no idea how well GRIB files are indexed for random access, it there is difference between png and JPEG2000 encoding, and how well the GDAL GRIB driver can utilize the possibilities that the format offer.

> That sounds good. IIRC GDAL is pretty mature with its memory management. 
>At least I haven't manged to crash it yet :D.

>> The most common raster format that Mapserver services are using is certainly GeoTIFF and when they are tiled, compressed, and have overviews they work pretty well. It is certainly an advantage if you can use the GRIB files directly without conversions. I see that you are using Mapcache in front of Mapserver and it will help a lot if you pre-seed the tiles. If you do not pre-seed then each time when the user is the first visitor on some site the bottle neck will be Mapserver.

> That is a good point! Especially as the forecast data is updated every 6 hours. I will have to integrate that into my update script somewhow once I got there.

>> The Ls/Hs idea is interesting. I do not believe there is anything ready available but I know that my colleagues at the Finnish Geodetic Institute have made quite nice things with Mapserver and shell scripts running some GDAL commands. Should they be computed on-the-fly for the area that is visible on the map?

> I'm doing some GDAL stuff in shell scripts for beta.saakeskus.fi at the moment. You can indeed do some fun stuff with the GDAL tools. In the long run, I was thinking of changing from bash scripts to Python, though, because then I can make some more calculations than are possible just with the GDAL tools.

> Yes, I was thinking if it was possible to do that inside of mapserver. 
Finding _the_ highest and lowest point is fairly trivial with GDAL. 
IIRC, gdalinfo can output that info by default. A little more challenging is finding all points which are highest or lowest among their neighbors. That's what's needed for a weather map because usually, you have more than one high and one low area on one map.

Gdalinfo -stats reports the min/max values but not their locations. As far as I know there is no GDAL tool or Python script in the GDAL samples that can do that. Users have been asking for such tool in the mailing lists and in gis.stackexchange so if you find of create such utility please let me know.

For finding the local min/max areas you could perhaps try the gdaldem tools https://gdal.org/programs/gdaldem.html. Areas with slope=0 should be what you are searching.

-Jukka-

> -Stefan

-- 
  (o_   Stefan Gofferje            | SCLT, MCP, CCSA
  //\   Reg'd Linux User #247167   | VCP #2263
  V_/_  https://www.gofferje.net   | https://www.saakeskus.fi

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