Here's a really fundamental question for project experts.
MapInfo's Lat/Long "projection" is really an equi-distant
cylindrical projection (from pg 419, pp 4 under "Projections
vs.Coordinate Systems"). But from what I read in Snyder's book on
projections used by the USGS, this projection requires 4
parameters: radius of the earth, central longitude and latitude,
and scale factor along the meridian.
My question is that if this is true, what does it matter what
datum you use? Note that the variable used in the projection is
the radius, not an ellipsoid axis. Why is there any choice of
Datum then? This appears to be a bit pointless unless MapInfo is
doing something else beyond the basic projection.
And where does MapInfo get its origin of lat and long from for
this projection? It looks like it might be the map window center,
but I need to know for sure.
Any ideas?
- Bill Thoen
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