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Thanks in advance for helping me with my issue. This GIS stuff is using parts of my brain that have remained idle since high school, and some parts are working faster than others.

I have land data stored as Albers projection and I want it converted to Lat, Lon so I can display it on Bing maps. The prj.adf file in the folder containing my data is this:

Projection    ALBERS    
Datum         NAD83    
Spheroid      GRS80    
Units         METERS    
Zunits        NO    
Xshift        0.0       
Yshift        0.0

Parameters    
  29 30  0.0 /* 1st standard parallel    
  45 30  0.0 /* 2nd standard parallel    
 -96  0  0.0 /* central meridian    
  23  0  0.0 /* latitude of projection's origin    
  0.0 /* false easting (meters)    
  0.0 /* false northing (meters)

I have been searching the web for said transformations, and have come close with the article by James Murtha (http://www.delphi3000.com/articles/article_4479.asp), but this apparently maps Lat Lon to his 1000 scale map, which is not the same scale as my data. The units described in my prj file show "Meters" - so do I need to calculate the number of meters between the 1st and 2nd standard parallel and assume that this is my unit size in the y direction?

Does anyone have any formulas (or links to information) that I can apply to map between (Lat, Lon) and the Albers (X,Y) projections? Sorry, but I do not have ARCGIS or any other tools to help me so I have to do this in native code without the conversion libraries in these tools.

Thanks - Steve Tufty

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I think your kinda stuck. The coverage file (just guessing because of the *.adf extension) is not going to be directly supported in any OPEN libraries that I know of. There are some free conversion tools but you would need to convert to another format. I could be wrong but that is what I think. –  Brad Nesom Feb 25 '11 at 17:23
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If you're going to code this yourself then (a) you need to learn about projections and (b) you can find the formulas--they cover most of a page--in Snyder's monograph Map Projections--A Working Manual (available from the USGS). Unless you intend to become a full-time GIS professional, you will likely find it much faster and more efficient to use existing software (or pay someone) to make this conversion. –  whuber Feb 25 '11 at 17:45
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2 Answers

You can use the Proj.4 library to convert coordinates from one projection to another. (However Proj.4 will not read your dataset - that is up to you) If you can't link to the library, then a stroll through the source code might get you the formula you are looking for.

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As whuber mentioned in the comments, doing this without any software support will be non-trivial, especially because you're doing a datum transformation. But if you do need the precise formulae, Map Projections: A Working Manual does have a section on Albers that would be useful. If you can use other software, then the open source Proj.4 library is the way to go. The GDAL library can access ArcInfo binary grids, so you could perform your translation like so:

gdalwarp -t_srs 'epsg:4326' path/to/hdr.adf wgs84-output.tif
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I guess it should rather be epsg:4326. –  Andre Joost Sep 22 '13 at 19:11
    
Ah, good catch -- it's now updated to be correct. –  scw Sep 28 '13 at 5:58
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