Hello Paul,
> Does anyone know why buffers become increasingly more inaccurate on certain
> bearings above distances of 4000+ Nautical Miles??
Large buffers have never been correctly implemented in MapInfo Professional. MapInfo
are fully
aware of the problem since I've nagged them about it several times - even more so
since v5.5
where buffers were split between Cartesian and Spherical flavours. Calling the
buffering
"spherical" is completely incorrect as the calculation is done in a planar fashion.
Basically, Pro takes a point (probably the first) in your object to buffer and
calculate "what is the
conversion of longitude (a unit of which changes with latitude) for the specified
buffer size". Of
course this is nonsense as a large buffer will cover area where the distance of a unit
of longitude
changes greatly. I have observed errors of 20%. The other problem with buffers is that
they are
always oval. As a buffer approaches the poles, it should "spread out" on a cylindrical
projection to
cover the line which represents 90N and 90S. Interestingly, the circle tool is
MapXtreme gets this
right!
IMHO, this is one of the most serious bugs in MapInfo. Given that professionals may
stake their
reputation on distances and areas, it really does need to be looked at immediately.
By the way, complex buffer performance is terrible in v5.5... I've gone back to v5.0.
Regards,
Warren Vick
Europa Technologies Ltd, U.K.
http://www.europa-tech.com
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