[Proj] Converting Mercator Meters to Degrees

[Eric Miller]

>>> On 2/1/2007 at 9:42 AM, Christopher Portka
<cportka at newwireless.com> wrote:
[snip]
> However, now I want to convert the easting (only the easting) to its

> appropriate
> longitude value.  Looking up the conversion from mercator meters
easting to
> longitude I get the following conversion:
> 
>    longitude = (MMEasting / 6356752.3142) * 57.295779513082322;
>    OR longitude = (easting / earthRadius) * RadToDeg;
> 
> But this gives me a slightly different value (about .1 degrees
smaller) than 
> if
> did the conversion with OGR like this:
[snip]
> I don't want to do this whole conversion though because I only need
the
> longitude.  Does anyone have an idea what I could be doing wrong in
my 
> longitude
> conversion?  Is there some kind of false easting or something that
gets set 
> in
> SetMercator that could be giving me differing values? I tried looking
at the
> source for SetMercator, but it doesn't look like it sets anything 
> differently. 
> Any help would be greatly appreciated.

You do know that the distance between lines of longitude varies by
latitude?  I don't know
why you don't want to do two transformations.  Why not UTM -> Geodetic
-> Mercator?  The
library has to do that anyway to go from UTM to Mercator.  So, you're
not saving yourself
much.