Problem with Oblique and Hotine oblique projections in proj?

[Dylan Keon]

Just for the benefit of the list - I never did reach a resolution using
PROJ with the Michigan Georef projection.

--Dylan


On 12/17/2004 10:43 AM, Ed McNierney wrote:
> Max -
>
> Dylan Keon ran into a similar problem with this projection back in
> August (searching the archives is a good idea!), and asked about it on
> the PROJ mailing list; I'm not sure he got a resolution.
>
> IMHO, it is highly unlikely that the CODE in PROJ is broken (although
> that's possible) and it's much more likely that there's something wrong
> with the parametric description of that projection.  I can't see
> anything obviously wrong with it, and Frank Warmerdam didn't notice
> anything obviously wrong back in August when Dylan reported the same
> problem.
>
>         - Ed
>
> Ed McNierney
> President and Chief Mapmaker
> TopoZone.com / Maps a la carte, Inc.
> 73 Princeton Street, Suite 305
> North Chelmsford, MA  01863
> ed at topozone.com
> (978) 251-4242
>
> -----Original Message-----
> From: UMN MapServer Users List [mailto:MAPSERVER-USERS at LISTS.UMN.EDU] On
> Behalf Of Clever, Max
> Sent: Friday, December 17, 2004 11:16 AM
> To: MAPSERVER-USERS at LISTS.UMN.EDU
> Subject: [UMN_MAPSERVER-USERS] Problem with Oblique and Hotine oblique
> projections in proj?
>
> Hello,
>
> I have been trying to project Michigan state plane coordinate shapefiles
> (EPSG:2253 or EPSG:102690 both are LCC) onto a Mapfile defined in
> Michigan Georef (EPSG:102123) which is a hotine oblique mercator.  I
> think Proj is miscalculating the reprojection because the state plane
> data is showing up in the area of the false northing and easting of the
> georef projection.  I have checked the parameters of the projection in
> the EPSG file and they are correct according to
> http://www.michigan.gov/documents/DNR_Map_Proj_and_MI_Georef_Info_20889_
> 7.pdf.  Also, I know that these parameters work when applied correctly,
> because I've written my own small VB program to convert coordinates from
> state plane to georef and back.  To check that proj was actually
> calculating the projections, I checked it by assigning the State Plane
> projection to the mapfile then projecting a shapefile in UTM zone 17
> onto it.  That was flawless, but once I switch the Mapfile back to
> Georef proj miscalculates.  To see where everything has been going I
> have set my extents to gargantuon numbers to encompass any possible
> placement of the projections and has helped me find where everything was
> going.
>
> So now, if it really comes down to getting dirty I think I might need to
> open up PROJ4's guts and check out what its doing wrong.  Hopefully
> though, I am the one that is screwing things up, so if anybody knows
> about how proj handles oblique mercators, I would be happy to hear any
> comments.