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Reprojecting Natural Earth

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Started 8 months ago by user4815162342
Latest reply from Nathaniel

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user4815162342
Member

For my first mapping project since college 15 years ago, I need the Natural Earth I 10m in a Lambert Azimuthal Equal Area projection centered on North America.

I'm limited to free tools -- I'm using Quantum GIS for building the map, but it can't reproject raster files. I found the very useful gdal utilities, and I think I have the command line figured out:

gdalwarp -s_srs EPSG:4326 -t_srs EPSG:2163 NE1_LR_LC_SR.tif NE1_LR_LC_SR_reprojected.tif

However, this leaves a large jagged gap through far northeastern Asia, which is going to end up still being visible in the upper left corner of my final map.

Does anyone have any hints or advice they can give me? Is there a better tool I can use?

Posted 8 months ago #
Nathaniel
Moderator

Congrats on getting back into mapping!

Can you post a screenshot of the problem area? It will help in diagnosis.

You could be suffering from a known issue with the GeoTIFF having a slight offset in the tag registration versus the .TWF registration. Or you could be using the wrong ellipsoids.

Posted 8 months ago #
user4815162342
Member

Here are some screenshots:

http://www.flickr.com/photos/45680204@N06/sets/72157623020406148/detail/

I've put an overlay of the 10m coast layer on a couple of the screenshots, so you can see that it almost does appear that data is missing from the output.

As far as the ellipsoids, I'm using the standard EPSG ID's for reference systems, which I obtained by reviewing the options available in Quantum GIS.

According to Quantum GIS, the source EPSG: 4326, points to WGS 84, or in the full Proj syntax: +proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs. I believe it said somewhere on this site that the Natural Earth maps are in WGS 84.

The destination is 2163, Lambert Azimuthal Equal Area -> US National Atlas Equal Area, or +proj=laea +lat_0=45 +lon_0=-100 +x_0=0 +y_0=0 +a=6370997 +b=6370997 +units=m +no_defs.

Posted 8 months ago #
user4815162342
Member

If there is a problem with my parameters, or how I'm trying to go about this, can anyone give me any ideas to try?

If it is a problem with the Natural Earth base map, does anyone have any ideas for a workaround until it can be fixed?

Posted 8 months ago #
Nathaniel
Moderator

Can you provide the latitude longitude extent that Quantum / GDAL thinks the raster image has? If it does not start at -180, 90 (but rather something like -180.xxxxxx, 90.yyyyyyyy) then it is likely the GeoTIFF problem. There is a way to over write the extents. You want it to read -180 and 180 on left right and 90 and -90 on top and bottom. The developer of the software we used to write out the GeoTIFFs is still looking into the problem and with the holidays in the US, this prob. won't be resolved for another week or two. If you can read in the .TWF and use those coordinates instead, you'll be good.

Posted 8 months ago #

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