Coordinate System – Converting Geotiff Web-Mercator into Azimuthal Equidistant Projection

convertcoordinate systemgeotiff-tiff

I have a geo-referenced tiff file, in the web-mercator projection; and I need it converted to an azimuthal equidistant projection.
I'm new to GIS and can't figure out how to do this.

I'm open to using any program for any OS, as long as it gets the job done.

And as far as OS-specific is concerned, I have computers with : Linux-Debian, Mac OX 10.6.8, Windows 7, and Windows XP.

Best Answer

Your source tif is in Pseudo mercator, but the extent stored inside the file is in degrees. This can not be interpreted correctly by gdalwarp, and so it delivers the untouched source file. You can get the correct extent in pseudo mercator coordinates from https://github.com/mapnik/mapnik/wiki/XMLConfigReference : -20037508.34, -20037508.34, 20037508.34, 20037508.34. With that, you can set the extent with gdal_translate manually before reprojecting.

The target projection is not covered by EPSG, but ESRI has invented a code 102016, which is included in GDAL and QGIS as EPSG:102016:

+proj=aeqd +lat_0=90 +lon_0=0 +x_0=0 +y_0=0 +datum=WGS84 +units=m +no_defs

You will get nasty artefacts along the 180° meridian, so an extra option SOURCE_EXTRA is needed. A blind spot on the north pole will remain, because pseudo mercator does not cover it:

gdal_translate -a_srs EPSG:3857 -of GTiff -a_ullr -20037508.34 20037508.34 20037508.34 -20037508.34 F:/Download/63575605298.3c.tif F:/Karten/merc_corrected.tif
gdalwarp -overwrite -s_srs EPSG:3857 -t_srs EPSG:102016 -ts 8192 8192 -wo SOURCE_EXTRA=1000 -of GTiff F:/Karten/merc_corrected.tif F:/Karten/world_aeqd.tif

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[GIS] How to use GDAL to convert from an arbitrary projection/datum into Equirectangular/WGS84

I've solved my problem.

RT90 is not a defined datum in Proj4. As such, GDAL just up and ignores the datum entry and applies the ellipsoid and projection correction.

It'd be nice if a warning was thrown at some point ("WARNING: datum 'RT90' not recognized" would be enough, but I digress).

The sinusoidal projection in WGS84 datum was transforming incorrectly because the Sinusoidal projection wasn't being set properly when export from Global Mapper. When I hand-rolled my own SRS to be "+proj=sinu +datum=WGS84" everything worked out fine.

To get proj4 to list various types of datums/projections/ellipsoids that it supports:

proj -ld    //lists known datums
proj -le    //lists known ellipsoids
proj -l     //lists known projections (use -lP for an expanded view)

If you want GDAL to work with unknown datum types, you must specify "+towgs84=" in your source SRS, and you must also specify "+towgs84=" in your target SRS if your target datum is not WGS84. These tags must be followed by 3 or 7 parameter transformation values, which can be found with some google-fu. More info on this tag can be found here:

http://trac.osgeo.org/proj/wiki/GenParms#towgs84-DatumtransformationtoWGS84

Hopefully anyone that runs into a similar problem will now be able to do so.

[GIS] Project twitter geo data into WGS84 map

"The world map certainly isn't in Mercator, but probably pseudo-Plate Carree (lat/lon just mapped as if they're linear units) or Plate Carree. Mercator stretches north-south, and you can see that the POIs are offset north and south versus the base map." [mkennedy]

"@mkennedy has provided the diagnosis (your world map is not in a Mercator projection). The implied solution is to treat (lon, lat) as (x, y), scaled to your world map (this is the "Plate Carree" projection), and you should get a close match. No inverse hyperbolic sine functions are needed :-)." [whuber]

Note: This is a summary of comments by @mkennedy and @whuber, so this question can be marked as answered.

Best Answer

Related Solutions

[GIS] How to use GDAL to convert from an arbitrary projection/datum into Equirectangular/WGS84

[GIS] Project twitter geo data into WGS84 map

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