- Are Stereographic, Polar Stereographic, and Oblique Stereographic really all the same projection?
- Is the latitute of natural origin for Polar Stereographic required to be 90 or -90? Shouldn't this be mentioned?
- Shouldn't all the sterographic projections include a scale at the origin?
- Why does the EPSG tables have a scale for Oblique Stereographic, but the (old) GeoTIFF definition doesn't?
- Why do the GeoTIFF parameters have such variable names for the different stereographic projections? PS uses StraightVertPoleLong and NatOriginLat, OS uses NatOrigin, and Stereographic uses ProjCenterLat/Long.
- In PJ_stere.c for PROJ.4 in function INVERSE(e_inverse) the calculation
of phi_l should likely test for a rho of zero (at the origin when xy.x and xy.y
are zero. Verify doing an inverse translation of position (0,0) with
pci_eg/sg.tif.
if( rho == 0.0 ) phi_l = asin(cosphi * P->sinX1); else phi_l = asin(cosphi * P->sinX1 + (xy.y * sinphi * P->cosX1 / rho));

- The PCI ps.tif file has a ProjNatOriginLatGeoKey. In PCI's PROJ.HLP
this number is called the latitude of true scale, but it carried through
to PROJ.4 as the +lat_0 value, not as +lat_ts (which it should perhaps be).
The Intergraph stereo_np.tif file has two lattitudes. One is the
ProjNatOriginLatGeoKey and the other is ProjCenterLatGeoKey. I imagine
that the ProjScaleAtNatOriginGeoKey and ProjNatOriginLatGeoKey are really
supposed to be equivelent to giving a latitude of true scale that isn't
the north pole (necessarily) if the scale is 1.0.
The current formulation includes a scale at the origin, but suggests that the origin must be either the north or south pole. Perhaps this is mixing up use of ProjCenterLatGeoKey to mark the pole with the use of an origin to establish the position of true scale (or alternatively to just give the scale at the origin). Is the solution to provide two formulations of polar stereographic, or to expect translators to boil their internal forumulations down to a pole indicator, and scale at the pole?

PCI: Upper Left Corner : 117d38'28.22" W Lon 33d54'13.08" N Lat gdalinfo: Origin (long/lat) = (-117.641,33.904) (117d38'26.91"W, 33d54'14.34"N)This amounts to approximately sixty meters of error in about 20000 meters. I don't know if this is a fundamental difference between GCTP and PROJ.4 or what. This should be reviewed at some point.

PCI: Upper Left Corner : 117d38'28.21" W Lon 33d54'13.08" N Lat gdalinfo: Origin (long/lat) = (-117.641,33.8682) (117d38'27.53"W, 33d52'5.42"N)

PCI: Upper Left Corner : 117d38'28.21" W Lon 33d54'13.08" N Lat gdalinfo: Origin (long/lat) = (-117.672,39.2717) (117d40'20.81"W, 39d16'18.19"N)I gather from the GCTP and PROJ.4 documentation that Robinson is only available as a spherical projection, and yet above was used with Clark 1866, which is not spherical. I would suggest that the problem might relate to different handling of non-spherical worlds, but this shouldn't account for the large difference. In general shouldn't we be keeping track of spherical projections and warning of use of non-spherical ellipsoids?

PCI: Upper Left Corner : 117d38'28.21" W Lon 33d54'13.08" N Lat gdalinfo: Origin (long/lat) = (-117.641,33.8653) (117d38'27.53"W, 33d51'55.12"N)

PCI: Upper Left Corner : 117d38'28.22" W Lon 33d54'13.08" N Lat gdalinfo: Origin (long/lat) = (-117.641,33.9035) (117d38'27.54"W, 33d54'12.51"N)

PCI: Upper Left Corner : 117d38'28.22" W Lon 33d54'13.08" N Lat gdalinfo: Origin (long/lat) = (-117.641,33.904) (117d38'26.91"W, 33d54'14.34"N)

PCI: Upper Left Corner : 117d38'28.22" W Lon 33d54'13.08" N Lat gdalinfo: Origin (long/lat) = (-117.641,33.9035) (117d38'27.54"W, 33d54'12.51"N)