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

[Jose Gonçalves]

Hi
When you chose the UTM projection with +proj=utm you should define the zone
with +zone=..., and avoid +lon_0.
The correct lon_0 of zone 12 is 111w.
Regards

José Gonçalves

2016-05-17 23:15 GMT+01:00 Dean Schulze <dschulze at wirelessseismic.com>:

>
> Thanks Andre.  Leaving off the lon_0 was the problem.
>
> ________________________________________
> From: proj-bounces at lists.maptools.org [proj-bounces at lists.maptools.org]
> on behalf of Andre Joost [andre+joost at nurfuerspam.de]
> Sent: Tuesday, May 17, 2016 12:09 PM
> To: proj at lists.maptools.org
> Subject: Re: [Proj] Using invproj to get back the inputs to proj
>
> 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
>
>
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