[Proj] MapInfo/Oracle Cylindrical Miller Parameters

[John Smart]

I don't know the details of what's going on inside proj, but I do see that if I take out the+towgs84 argument I get:
C:\Proj\bin>cs2cs +proj=latlong +datum=WGS84 +to +proj=mill +ellps=clrk66 +lon_0=0 +units=m
2.35 48.85
261603.65       5916486.09 0.000

which is closer to your Oracle results. clrk66 doesn't seem like the right ellipsoid for WGS-84 but (a) I can never remember how to get a list of ellipsoid codes from proj and (b) even a sphere would probably do the job for a "world projection". And NAD27 is for North America - a best fit as of 1927 knowledge. But your test point is in Europe. So I wouldn't expect your +towgs84 values to be useful there.

I think you should keep in mind that if you're talking about a world projection, you're talking about scales in the order of 1:100 million, where even a skinny 0.1mm line width will cover 10km on the ground. The odd metre or two or thousand won't make much difference.

  ----- Original Message ----- 
  From: Patrick Mézard 
  To: proj at lists.maptools.org 
  Sent: Thursday, January 12, 2006 7:07 AM
  Subject: [Proj] MapInfo/Oracle Cylindrical Miller Parameters


  Hello,
  In search of a good-looking world projection I came across Miller Cylindrical one. Fortunately, both MapInfo and Oracle Spatial know about it, and even better agree on transformations from WGS84 to Miller for several points. This is important because it is always easier to debug something when the input or output can be reproduced on other tools. Now I would like to use it in proj.4 but as usual I am stuck trying to figure out *the parameter string*.

  I am taking the Oracle WKTEXT description as reference:
  """
  PROJCS["Miller Cylindrical", GEOGCS [ "NAD 27 (Continental US)", DATUM ["NAD 27 (Continental US)", SPHEROID ["Clarke 1866", 6378206.400000, 294.978698]], PRIMEM  [ "Greenwich", 0.000000 ], UNIT ["Decimal Degree", 0.01745329251994330]], PROJECTION ["Miller Cylindrical"], UNIT ["Meter", 1.000000000000]]
  """

  It converts (2.35, 48.85) into (261360.667, 5916639.52).

  NAD27 datum is defined by:
  """
  NAME = NAD 27 (Continental US)
  SHIFT_X =  -8
  SHIFT_Y =  160
  SHIFT_Z = 176
  """

  Oracle WGS84 and Clarke 1866 ellipsoids definitions are the same than proj.4 ones.

  and finally tried something like:
  """
  cs2cs +proj=latlong +datum=WGS84 +to +proj=mill +ellps=clrk66 +towgs84=-8,160,176 +lon_0=0 +units=m
  2.35 48.85
  261360.67       5889006.49 -12281.453
  """

  So, cs2cs output x coordinate perfectly matches Oracle's one, but the y differs by 27633m.
  I tried to replace the Clarke ellipsoid with a sphere defined by the minor then the major axis but it does not improve the result.

  Just to be clear: I do know that configuring Miller projection with a WGS84 datum would give me usable results. What I am looking for is compatibility with existing applications, to ease debugging and allow release to third parties without complicated explanations about why this is not the same thing than the one they see in their GIS dialog boxes while having almost the same name.

  What do you think about this? Are these discrepancies to be expected because of differences within projection implementations? Did I miss something when configuring the projection?
  Thank you for any idea.

  --
  Patrick Mézard





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