Problem with Oblique and Hotine oblique projections in proj?

[Ed McNierney]

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.

Also here is the portions of the mapfile that are pertinent to this
message:

MAP
NAME zooba.map
STATUS ON
SIZE 400 400
EXTENT 129827.580 41110.205 823355.654 889381.112 #EXTENT 13067766
660421 13155653 722085 UNITS meters SHAPEPATH "c:\webgisdata\zooba\v1c\"
SYMBOLSET "c:\ms4w\Apache\htdocs\zooba.org\zoobastart\gis\symbols.sym"
IMAGETYPE png24
FONTSET "c:\ms4w\Apache\htdocs\zooba.org\zoobastart\gis\fonts.list"

#GEOREF PROJECTION BASED USING GRS80 ELLIPSOID IN METERS PROJECTION
   "init=EPSG:102123"
#   "proj=omerc"
#   "lat_0=45.30916666666666"
#   "lonc=-86"
#   "alpha=337.255555555556"
#   "k_0=0.9996"
#   "x_0=2546731.496"
#   "y_0=-4354009.816"
#   "ellps=GRS80"
#   "datum=NAD83"
#   "units=m"
#   " no_defs"

#  "init=EPSG:2253"	
END #PROJECTION

  QUERYMAP
    STATUS ON
    STYLE SELECTED
    COLOR 255 255 0
  END

LAYER
  NAME easements_4_27_04.shp
  TYPE Polygon
  TRANSPARENCY 50
#  maxscale 1500000
  STATUS on
  PROJECTION
    "init=epsg:102123"
  END #PROJECTION
  DATA easements_4_27_04
  HEADER 'easements_4_27_04.shp_header.html'
  TEMPLATE easements_4_27_04.shp_query.html
      CLASS
        Name 'Easements'
        COLOR 100 100 231
        OUTLINECOLOR 0 0 0
      END  # CLASS

END  # LAYER

LAYER
  NAME geoeasements_4_27_04.shp
  TYPE Polygon
  TRANSPARENCY 50
  maxscale 1500000
  STATUS on
  PROJECTION
    "init=EPSG:102690"
    #"+proj=lcc"
    #"+lat_1=43.66666666666666"
    #"+lat_2=42.1"
    #"+lat_0=41.5"
    #"+lon_0=-84.36666666666666"
    #"+x_0=3999999.999984"
    #"+y_0=0 +ellps=GRS80"
    #"+datum=NAD83"
    #"+to_meter=0.3048"
    #"+no_defs"
    #"no_defs"
  END #PROJECTION
  DATA Geoeasements_4_27_04
  HEADER 'easements_4_27_04.shp_header.html'
  TEMPLATE easements_4_27_04.shp_query.html
      CLASS
        Name 'Geoeasements'
        COLOR 255 138 231
        OUTLINECOLOR 0 0 0
      END  # CLASS
END  # LAYER