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

[Thomas Knudsen]

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>:

> 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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