[Proj] Using invproj to get back the inputs to proj

[Andre Joost]

Am 17.05.2016 um 16:54 schrieb Dean Schulze:
> Leaving off the -r on invproj gives me back the correct latitude, but the longitude is even worse:
>
> $ proj +proj=utm +lon_0=112w +ellps=clrk66 -r man.page.lat.lon.txt | invproj +proj=utm  +ellps=clrk66
> #	proj +proj=utm +lon_0=112w +ellps=clrk66 -r man.page.lat.lon.txt
> #	Should give
> #		460769.27     5011648.45
> 3d30'W	45d15'33.1"N
> 3d30'W	45d15'33.1"N
> 3d30'W	45d15'33.1"N
>
>
> ________________________________________
> From: proj-bounces at lists.maptools.org [proj-bounces at lists.maptools.org] on behalf of Thomas Knudsen [knudsen.thomas at gmail.com]
> Sent: Monday, May 16, 2016 11:59 PM
> To: PROJ. 4 and general Projections Discussions
> Subject: Re: [Proj] Using invproj to get back the inputs to proj
>
> Try to leave out the -r option in invproj: the output of proj, that you feed into invproj is not in reverse order.
>
> Also, do not expect identical output, especially not for data points far off the central meridian.
>
> /Thomas
>
> Den 16. maj 2016 19.26 skrev "Dean Schulze" <dschulze at wirelessseismic.com<mailto:dschulze at wirelessseismic.com>>:
> Following the example in the man page if I do
>
>      proj +proj=utm +lon_0=112w +ellps=clrk66 -r man.page.lat.lon.txt
>
> where the file man.page.lat.lon.txt contains
>
>      45d15'33.1"   111.5W
>      45d15.551666667N   -111d30
>      +45.25919444444    111d30'000w
>
> I get the 3 lines of output shown in the man page:
>
>     460769.27    5011648.45
>     460769.27    5011648.45
>     460769.27    5011648.45
>
> So far, so good.  But when I try to use invproj to get back the original inputs the results are not even close to the inputs:
>
>      proj +proj=utm +lon_0=112w +ellps=clrk66 -r man.page.lat.lon.txt | invproj +proj=utm +lon_0=112w +ellps=clrk66 -r
>
> gives
>
>      73d25'28.89"W       3d18'2.678"N
>      73d25'28.89"W       3d18'2.678"N
>      73d25'28.89"W       3d18'2.678"N
>
> What is invproj giving me?  How do I run invproj to get back my original inputs?
>

You have missed the lon_0 in invproj, so it takes it to Greenwich.

HTH,
André Joost