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

[Dean Schulze]

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.