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

[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?

Apparently invproj doesn't use command line parameters the same way that proj does.  Is this documented somewhere?  I've read the 3 .pdfs provides as users manuals, but they say nothing about how to use invproj to get back the original inputs.

Thanks.
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