[Proj] Need help converting Goode to latlon

[Gerald I. Evenden]

On Thursday 23 July 2009 1:12:02 pm David Turover wrote:
> On Thu, Jul 23, 2009 at 10:56:19AM -0400, Gerald I. Evenden wrote:
> > On Thursday 23 July 2009 1:14:46 am David Turover wrote:
> > > The jpeg is the result of attempting to reproject from Goode to
> > > geographic coordinates. I have confirmed with an ESRI tool that the
> > > original shape is in Goode, so the problem is in my use of proj.
> >
> > I am sorry, but the above sentence makes no sense to me.  What does the
> > jpeg figure have to do with anything then?  It is not a representation of
> > "geographic coordinates" but a display of said coordinates in a
> > particular projection.
>
> The jpeg shows my Goode-to-latlon results laid onto Google Earth as
> coordinate-based KML so my output can be compared against Google Earth's
> known-good representations of country positions in lat/lon coordinates.
> Since they do not line up, I am doing something wrong. I hoped the picture
> might offer more experienced people a hint as to the specific problem.

I do not know when Google became the benchmark for projection stardards but 
that is another issue.  Secondly, comparing results graphically, especially 
with a projection like nsper, leaves something to be desired.

In the future, I woult strongly suggest that in seeking verification of 
projection operations that a short, randomly selected collection of the 
source data values being converted be given and simply ask for a conversion 
of these values from a knowledgeable source.

> > It would appear that your original data is in Goode projection
> > coordinates and you want to *inverse project* these values to geographic
> > coordinate.
>
> I forgot to mention that I have been adding "+inv" to the proj arguments
> programmatically. When I get into work I will make sure this is working
> and I will also try leaving it off to see if that makes a difference.
> Let's watch this be the source of the problem since it is something that
> I should have mentioned two days ago.

I have no idea what "+inv" is so I assume it is part of Warmerdam's version.  
Early proj and lproj use -I runline option to designate inverse projection.

#!/bin/bash
# run off a few test examples of Goode projection
lproj +proj=goode +R=6378137.0 <<EOF >test_cart.dat
0 45
-80 30
-120 -10
60 50
10 10
EOF
#
# run the cartesian file back to geographic coordinates
#
lproj -I +proj=goode +R=6378137.0 <test_cart.dat >test_geog.dat
#
echo done

after running above script:

gie at charon:~/tmp$ m *.dat
::::::::::::::
test_cart.dat
::::::::::::::
0.00    5003479.28
-7712440.56     3339584.72
-13155395.71    -1113194.91
4563799.12      5536706.32
1096282.98      1113194.91
::::::::::::::
test_geog.dat
::::::::::::::
0dE     45dN
80dW    30dN
120dW   10dS
60dE    50dN
10dE    10dN
gie at charon:~/tmp$

OK?

> > I think there is a great communication problem here.
> >
> > Basic questions:
> >
> > 1. what are the original coordinates you are dealing with?  Goode
> > cartesian? 2. What is the central meridian used by the Goode projection
> > to create these coodinates?
> > 3. What earth radius and units were used in the projection?
> >
> > These questions *must* be answered before using any projection procedure.
>
> 1. The input projection is "Goode_Homolosine_6378137_sphere". The
> coordinate values are decimal numbers six figures long plus a fractional
> amount. The full projection definition is here:
> http://segfault.cs.sonoma.edu/~dturover/gisbug/Goode%20Homolosine%206378137
>%20sphere.prj
>
> 2. The central meridian is Greenwich.
>
> 3. Input units are meters, output units are degrees. The earth radius in
> the input projection is 6378137.0.
>
>
>  - David T.
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