-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED]]On Behalf Of Steve Wallace
Good question. I'm not sure how MapInfo handles object variables in
MapBasic. Since there is no map at the time, thus no projection clause or
bounds, I can't see how they would be affected.
===============
I will try to express my understanding of that feature. I equate object
variables to object definitions in a MIF file. The numbers representing the
coordinates may be entered with any number of decimal places. They are only
theoretically constrained by the CPU precision (number of significant
decimal numbers) and they are meaningless geographically speaking without
the CoordSys clause. When the mif file is read in, or when the object
variable is inserted in a table, then these values are converted into a MI
map, with its precision level as given by its bounds clause (or its default
values).
Imagine you have created some objects in a mif file format, using a sizeable
amount of decimals (let us say 9 for a lon-lat unbounded table). Import that
file and export it as a new mif file. You may find that the newly exported
numbers may differ from the ones you entered in the original mif; the
differences are not only due to truncation, they come also from some
"roundings" resulting from the decimal conversions of the integer internal
grid positions. And the results may vary if you change the range of the
bounds.
Object variable coordinates obtained from a MI map (via extractnode,
centroid ...) are already "rounded to internal grid positions" as in the
exported mif file; therefore no differences could be expected if a procedure
equivalent to the above was followed.
Almost in the same line, I can add that narrowing bounds on an existing
table will not change the internal precision of the already existing objects
because their MI map coordinates have already been rounded to grid
positions; they will "benefit" from the higher precision only if they are
edited (and where they are corrected). New objects will of course be in the
new precision setup. Changing bounds may even create problems : objects can
be distorted if the new internal grid does not overlay perfectly on the old
one. One will have to defined the new bounds in a way to respect that
requirement.
This last point supports may earlier warning not to overlay map with
different bounding conditions.
Jacques Paris
e-mail alternate
[EMAIL PROTECTED] [EMAIL PROTECTED]
paris PC Consult (mainly MapInfo app.)
www.total.net/~rparis/gisproducts.htm
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