I am using a tool which uses proj4 lib to project maps.

I have a set of xy coordinates to be converted to latlongs with that tool. as I have the source projection string say

+proj=aea +datum=NAD83 +ellps=GRS80 +lon_0=-96d +lat_1=45d30 +lat_2=29d30 +lat_0=37d30 +x_0=000000 +y_0=00000

if I pass

+proj=longlat +datum=NAD83 +ellps=GRS80 +lon_0=-96d +lat_1=45d30 +lat_2=29d30 +lat_0=37d30 +x_0=000000 +y_0=00000

as the destination projection

Will it give me a LAT LONG from the x,y supplied?

I know there are ways to write code and do inverse projection to get latlong, but I wanted to bypass that and use x,y as the input to the tool I have and get latlong from it by just using the proj4 string.

  • I ment "as the destination projection will it give me a LAT LONG from the x,y supplied"
    – user1541
    Commented Dec 28, 2010 at 15:22
  • Does the edit help make the question clearer?
    – Brad Nesom
    Commented Dec 28, 2010 at 16:32

1 Answer 1


You don't need the "+lon_0=-96d +lat_1=45d30 +lat_2=29d30 +lat_0=37d30 +x_0=000000 +y_0=00000" in the proj=longlat since it's LonLat and not a projected system.

If both systems have the same datum and ellps you're fine, else you maybe need to provide the +towgs84 parameter with datum-transformation parameters.

  • I guess the tool that I have doesent take proj4 strings with just proj= defination in it, as its giving me error / unexpected termination. Is there any tools online that gives us a source projection to destination projection conversion (and we specify both the projection strings). ?
    – user1541
    Commented Dec 30, 2010 at 16:20
  • user1541 espg.io gives "towgs" helmert coefficients for all datums you're likely to use. For example Airy 1830 is: TOWGS84[446.448,-125.157,542.06,0.15,0.247,0.842,-20.489], Commented Jan 15, 2020 at 11:36

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