> [mailto:[EMAIL PROTECTED]]On Behalf Of Mike Merelie
> Sent: March 15, 1999 5:29 AM
> Subject: MI Drawing problems
> Using MapInfo 4 drawing objects on the cosmetic layer. When zoomed in very
> close the nodes are placed at the desired location. On zooming out the
> nodes appear to shift location. The shape of the object remains OK but
it's
> location is offset.
>
You have hit one manifestation of MapInfo internal precision. Coordinates
are stored as integer values of a maximum given size, and the measure of
that precision, i.e. the minimum distance between two distinct points
depends on actual circumstances (nature of the projection and actual
distance taken into account). By playing with bounds, one can change that
internal precision. But there are limits.
Cosmetic layer is an area where the internal precison is always 1/1 000 000
of a degree, because even if it is in a mapper that has a named projection,
it is still taken by MI as a simple lon/lat map.
If your mapper is not in lon/lat, or in lon/lat with higher internal
precision defined by narrower bounds, then the basic grid of the mapper will
not coincide with the basic grid of the cosmetic layer (basic grid is made
of the discrete positions that internal coordinates can take; ex. in lon/lat
the 0.000 001 degree or 11.11cms in lat).
My recommendation is that one should never use the cosmetic layer to draw
objects that should be "topologically sound" relatively to objects in other
layers that are not in plain lon/lat.
Jacques Paris
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e-mail [EMAIL PROTECTED]
gis activity (MapInfo mainly)
http://www.total.net/~rparis/gisproducts.htm
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