HPGN Datum?

[Bill Binko]

Hi everyone,

I found an excellent site for Florida map data:

http://www.fgdl.org/

Some of their data is a bit out of date, but there is a nice selection,
and it's all in the same projection, even from a wide variety of sources.

My problem is that they use a datum that I haven't seen before "HPGN".
Here is the projection info from their metadata:

MAP PROJECTION PARAMETERS:

  Projection                           ALBERS
  Units                                METERS
  Datum                                HPGN
  Spheroid                             GRS1980
  1st standard parallel                24   0  0.000
  2nd standard parallel                31  30  0.000
  Central meridian                    -84   0  0.000
  Latitude of projection's origin      24   0  0.000
  False easting (meters)               400000.00000
  False northing (meters)              0.00000

After some looking around, and some advice from the board a few weeks ago,
I used these projection instructions in Mapserver (CVS Head):

PROJECTION
      "+proj=aea"
      "+lat_1=24"
      "+lat_2=31.5"
      "+lat_0=24"
      "+lon_0=-84"
      "+x_0=400000"
      "+y_0=0"
      "+ellps=GRS80"
      "+datum=NAD83"
      "+units=m"
      "+no_defs"
END

It seemed the "NAD83" was close enough to the "HPGN" datam.  Now I'm
seeing small problem when combining any of the data from this source with
others that are in the Florida West projection (espg:26759), and I'm
suspecting that the bad datum is the problem.

Actually, I'm hoping that's it because if it is, I'm confident someone
here can help me get it right: if not, it means the data's bad :-(

An example of the "wrongness" can be seen at:
http://www.binko.net/badProj.png

The roads should line up within the parcels.  The roads are in HPGN, and
the parcels are in espg:26759

Any help would as always be appreciated.


Bill

PS: Paul R: you did say you loved projection problems, right? :-b