I'm trying to create a specific projection with QGIS (something like that: +proj=lcc +lat_1=69.75 +lat_2=52.87 +lat_0=61.31 +lon_0=7.665 +x_0=0 +y_0=720 +ellps=GRS80 +units=m +no_defs). I have some grib files which contain these informations:

Input geometry:

Data comes from: 233 255 38 Projection : 3 Nlon,Nlat,Nlev : 720 800 65 South,West : 52.870000000000005 7.6650000000000000 North,East : 69.756418673948701 45.483402182515576 Dlon,Dlat : 2500.0000000000000 2500.0000000000000 Projlon,Projlat(1,2) : 20.000000000000000 62.399999999999999 62.399999999999999

Scan: WE:SN winds(grid) Lambert Conf: Lat1 52.870000 Lon1 7.665000 Lov 20.000000 Latin1 62.400000 Latin2 62.400000 LatSP 0.000000 LonSP 0.000000 North Pole (720 x 800) Dx 2.500000 Dy 2.500000

And I have my image (800 x 720) with top left corner at (0,0). The aim of this personnal projection is to put images in Lat Lon in WGS84.

How can I create this projection?

  • 1
    You can go to settings/ custom CRS. You have to choose the plus icon (add a CRS) then give a name put your crs string in the parameters section. You can test your settings also, just give a lat lon coordinates in WGS84 datum and see if the results are ok. If everything is working fine you have to choose ok. The new crs will be given an ID code and it will appear under "user defined coordinate systems" section in the CRS tool (the one that ask for the crs when a layer has no crs, or you are reprojecting) – Gerardo Jimenez Jun 8 '16 at 13:23
  • I see where now but what is the good crs string in the sight of these settings (for example the fact that 1px=2.5km)? – Maxime Blériot Jun 9 '16 at 4:13
  • I personally made some custom crs for Mexico (UTM and INEGI CCL). The way I test with scanned maps is First georeference the image and then I create a vector Grid in MMQGIS and superimpose it over the georefenced image. If my vector grid coincides with the grid of my map things are OK. As mentioned before I tested, for instance with a georeferenced soil map (1: 50,000) and a vector grid of 1 km and have excelent results. Is this what you have in mind? – Gerardo Jimenez Jun 9 '16 at 13:36
  • In fact, I have 2 differents ways to resolve my problem. I need to compare 2 images pixel by pixel which have differents map selection (Europe for one, Scandinavia for the other). First way: I need coordinates (Lat/Lon) for each pixel of my scandinavia image (which is a png file extracted from Grib file thanks to a Matlab script). After that, I could compare pixel by pixel the scandinavia area with Europe area. (I want to do that but I don't know how to have Lat/Lon for each pixel). Second way: I reproject my scandinavia image in Lat/Lon and then I compare my 2 images. – Maxime Blériot Jun 9 '16 at 17:38

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