----- Original Message -----
From: "George M. Smith" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Thursday, August 31, 2000 8:27 PM
Subject: Re: MI How does MapInfo handles muliple Projections in the same
window?
> Spencer and Steve
> Are you referring only to the accuracy of on-the-fly transformations
only??
> Our checking of conversion of point data from one coordinate system to
> another including a different datum finds the results from MI to be
> identical to those from the Geographic Calculator to greater than 3 and I
> dont recall how many more decimal places. Are the claims of accuracy of
the
> Geographic Calculator in question or are the algorithims for the
on-the-fly
> transformation different for those for converting point data???
I don't know what the Geographic Calculator does. This inaccuracy for
on-the-fly transformations is well documented in the manual for MapInfo
Professional: It occurs when converting between projections in different
datums
(data?). A conversion between two projections based on the same datum will
not introduce any error.
Also be aware that some datums that are thought of as "different" are
really the same datum, and conversions between these datums probably
won't introduce any error. GRS80 and WGS84 come to mind.
There is another exception: when converting between the 1927 North American
Datum (NAD27) and the 1983 North American Datum (NAD83). MapInfo has
implemented the more accurate (but slower) NADCON algorithm developed by
the US Army Corps of Engineers.
Hope this helps.
Spencer
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