[GIS] USA Albers Equal Area Conic USGS version (LANDFIRE) projection not read by R

coordinate systemr

I am working with the North America Forest Dynamics dataset. As mentioned it uses the USA Albers Equal Area USGS version projection, which is primarily different from the USA Albers Equal Area projection in the measure of the latitude of origin (former is 23 and latter is 37.5).

The datum is clearly read by Arc as D_NorthAmerica 1983. which is the datum. However, this datum information is not read by R (using raster package). Hence, resulting analysis and written rasters have unknown datum when processing is done in R.

Interestingly, the famous spatial reference website does not have a Proj4 string info for this, which I could manually input into the crs() command. But on the same website, the .Prj file can be downloaded and on opening this ile as a text pad file a datum i.e. North America 1983 datum and hence transformation is mentioned.

Why is R not recognizing the datum around which the transformation has to happen for this projection?

Best Answer

I created a small TIFF from the data selector on that site. gdalinfo reports this:

PROJCS["unnamed",
    GEOGCS["NAD83",
        DATUM["North_American_Datum_1983",
            SPHEROID["GRS 1980",6378137,298.2572221010042,
                AUTHORITY["EPSG","7019"]],
            TOWGS84[0,0,0,0,0,0,0],
            AUTHORITY["EPSG","6269"]],
        PRIMEM["Greenwich",0],
        UNIT["degree",0.0174532925199433],
        AUTHORITY["EPSG","4269"]],
    PROJECTION["Albers_Conic_Equal_Area"],
    PARAMETER["standard_parallel_1",29.5],
    PARAMETER["standard_parallel_2",45.5],
    PARAMETER["latitude_of_center",23],
    PARAMETER["longitude_of_center",-96],
    PARAMETER["false_easting",0],
    PARAMETER["false_northing",0],
    UNIT["metre",1,
        AUTHORITY["EPSG","9001"]]]

and R reads it and reports this:

> r = raster("./sdat_1290_1_20180804_101230826.tif")
> crs(r)
CRS arguments:
 +proj=aea +lat_1=29.5 +lat_2=45.5 +lat_0=23 +lon_0=-96 +x_0=0 +y_0=0
+ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs

The "datum" info is encoded in the +ellps=GRS80 and the +towgs84=[zeroes] parameters. What's missing is the "name" in the DATUM section, namely, "North_American_Datum_1983", but I don't think these are official text strings in any sense. Some notes here on that: How are ESRI WKT projections different from OGC WKT projections?

So R is reading the correct data, and projections and transformations should work correctly.

Related Question