PyProj: Mapping latitude/longitude onto rectangle using x,y coordinates

Question

I have a series of latitude/longitude coordinates that I'm trying to project onto a map as x,y coordinates.

I'm using the https://code.google.com/p/pyproj/ library to convert the coordinates, I can't seem to find anywhere that explains what the output of the functions mean though?

import PyProj

def ConvertToMapProjection(Coordinates):
    ''' Projects a mapped pair of coordinates onto a map '''

    # Define the projection
    RobinsonProjection = pyproj.Proj("+proj=robin +lon_0=0 +x_0=0 +y_0=0 +ellps=WGS84 +units=m +no_defs")

    East, North = RobinsonProjection(Coordinates[0],Coordinates[1])

    return [East,North]

ConvertToMapProjection([51.5072,0.1275])

returns:

[4866232.474090106, 13636.369990048854]

It's not clear what the units are? What's the best way to map this onto a 900 x 1100 rectangle?

Answer 1

Default units of proj are meters (you even specify it in the command).

The referential ellipsoid you're using is WGS84, which has mean radius 6356752.3142 meters (see proj -le)

You can scale it down by this factor to get "unit ellipsoid":

$ proj +proj=robin +ellps=WGS84 -m 1:6356752.3142

Even easier, but not so precise, would be projecting using the unit sphere:

$ proj +proj=robin +a=1

The answer to second part of your question is outlined in this post.