This came up again in one of the meetings today at MapWorld. The "Lat/Long
Projection" is what I would call the "chameleon" projection. There is no
datum assumed -- I don't understand either. Anyway, since there is no datum,
there is no conversion when you "save copy as..." with a datum (like
Lat/Long NAD27). All it does is append the coordinate clause to the existing
data -- no transformation takes place.
When you open a table with "lat/long" into a mapper that has tables opened
already that DO have datum, no transformation or reprojection takes place.
The "lat/long" simply assumes it is in whatever datum the existing mapper is
in. Where this really killed me was when I was first creating MI Pro 2.1
tables in the default "lat/long" over NAD27 street files. Then when I opened
those same files over newer data in NAD83, the polygon edges didn't match up
where the should have. My data thought it was NAD27 when it was digitized,
but now it opens over a NAD83 projection and thinks transformation is not
necessary.
To me, even having this "projection" is dangerous. If you have x/y data you
need imported, then you need to know in what datum that source data was
created.
Steve E. Wallace
GIS & Market Information Manager
Florida Farm Bureau Insurance Companies
----- Original Message -----
From: <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Tuesday, May 25, 1999 4:15 PM
Subject: Lat/Long MI datum?
> When a MapInfo table is in the first Lat/Long category what datum is this
> projection using? When I look into the Mif file it indicates 1, 0. 1
being
> Lat/Long, and 0 being the datum. What kind of datum is this category
using?
>
>
>
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