Michel,
Thanks for the feedback. I have loaded an update
(http://www.acenet.com.au/~pwaight/spatialsql_download.htm) with the following notes:
1.. Correction to Region Visual Centroids calculation. Previously larger regions
caused MapInfo to hang or crash.
2.. Support for geographic and non-geographic projections. Tested on metric/imperial
projected coordinate systems.
3.. Error checking improved. Green target symbol added to computation layer to
indicate regions where VC not created due to geometry shape (eg. long, thin regions)
or memory restrictions.
4.. Performance improved (1, 50 point region / 0.2 sec; 1, 500point region / sec; 1,
2000pt region / 2 secs; 1, 15000 pt region / 180 secs). So for region sizes less than
5000 points, could be run in interactive time frames, otherwise as a batch process.
Regions above about 50000 nodes are not recommended in the current version. The
centroid of the region is updated with the VC value, so the expectation is that the
process is run once for a data set. It is then possible to load these values into user
data columns (Xvc,Yvc) if it is necessary to restore the geometric centroid as an
alternative point.
Given the time, I have plans to improve performance for the more complex polygons and
to calculate the 2nd VC formally, providing the user with options to load VC1, VC2 as
user data. For example, this would then permit rapid evaluation of alternative (or
multiple) label points. As is stands, there is sufficient data for someone wishing to
do this by erasing from a temp copy of the original region and rerunning the process.
Phil Waight.
_______________________________________
SPATIAL PROJECTS
Ph (61)02 48617977
0418 647697
Fx (61)02 48617977
Email : [EMAIL PROTECTED]
Web: www.acenet.com.au/~pwaight
----- Original Message -----
From: "Michel Wurtz" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Tuesday, September 28, 2004 12:21 AM
Subject: Re: MI-L spatialSQL v1.50 - region visual centroids
Phil Waight a �crit :
> See a definition of region centroids:
> http://www.acenet.com.au/~pwaight/spatialsql_centroids.htm
> Implemented to assist label placement:
> http://www.acenet.com.au/~pwaight/spatialsql_labels.htm
> Download: http://www.acenet.com.au/~pwaight/spatialsql_download.htm
>
> The default and visual centroid function is available from the spatialSQL menu as a
> free tool. The label functions are available as a 30 day trial.
I'm happy, because the "visual centroid" definition is the same as mine.
Then I downloaded SpatialSQL and try the visual centroid function (which
is on my todo list).
Unfortunately, it takes ages and eventually crashed as i tried it on the
whole of French counties.
I ran it on a smaller set of polygons (4) and it takes 15 minutes to
terminate... saying 0 updated. Figuring that 770+ vertex polygons may
slow the process :-) , I tested visual centroid on a better shaped
polygon, and it works much more faster.
Unfortunately, it seems that only lat/long projections are supported
and that the time of processing is exponential when the number of
points increases, hence unusable for many applications...
--
Michel Wurtz
MAAPAR/DGA/SDSI/CERIT/DIG
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