# [Proj] Need help converting Goode to latlon

David Turover dturover at student.santarosa.edu
Thu Jul 23 12:12:02 EST 2009

```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.

> 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 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.
```