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

Dean Schulze dschulze at wirelessseismic.com
Tue May 17 09:54:06 EST 2016

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.


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


    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.

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