My thoughts at present are thus. For me, this is about a problem that I have been presented with where I have 6000 odd paddocks each with a district tag on them, and I wish to make a nice map of districts. The paddocks are both contiguous and disjointed. A simple combine using column yields a result of very disjointed complex polygons. What I really want is a sort of veroni tool for polygons.
My thoughts on a strategy is as follows:
1.Create a table of points representing all nodes with the fields of RefColValue, X, Y.
2.Do a groupby SQL on X ad Y and count the number of points for each X and Y combination.
3. I then delete all points where the count > 1 (these represent nodes as these represent the contiguous nodes between adjoining polygons)
4. At this point there should be only points along the outside edges of paddocks, with points from nodes along contiguous edges deleted
5. Create Veroni polygons of these points
6. Erase the areas covered by the original polygons from the veroni result
7. Add these bits back to the original
8. Do a combine using column now, and it should combine the remnants of the veroni polygons along the outer edges with the original polygons to create polygons with gaps between filled?
r
On Mon, 31 May 2004 12:59:47 +1000, Phil Waight <[EMAIL PROTECTED]> wrote:
I think the general problem is called the "Geodesic ham sandwich". A reference is: www-ma2.upc.es/~hurtado/ham.pdf. I didnt understand the words in this paper but fortunately there are pictures. So with any 2 regions that may or may not intersect, itspossible to find a median line string which you could then use to reform the regions.
I think you are right in that buried in a Voronoi diagram of all the points might be a solution. But how do you find it? (In cases of sets of points from circles it might be easier, but what about regions).
Next question is "Is there another solution using good old trusty MapInfo buffers and a lot of cpu cycles?"
ps. I googleflopped on the search: "MapInfo & ham sandwich".
Phil.
----- Original Message ----- From: "Robert Crossley" <[EMAIL PROTECTED]> To: "Apers Mathieu" <[EMAIL PROTECTED]> Cc: "MapInfo List" <[EMAIL PROTECTED]> Sent: Monday, May 31, 2004 9:07 AM Subject: Re: MI-L RE: Buffering query - v2
Mathieu,
From your comment, I'd imagine that what you are after is the equivalent
of a cross between buffers and veroni polygons for points, that is a
buffer that follows the mid-line between two polygons if they are less
than two buffer widths apart.
I posted a question about this a while ago and did not get any good
leads. I would actually be interested in making such a tool, but could
not think of an efficient way of proceeding with this. One thought was to
drop the polygons to constituent points and create veroni polygons of the
points. It did not work for points which were coincident. I really did
not spend much time on it, so would be interested in thoughts. As I write
this, some new ideas are emerging from the weekend murk.
BTW, most of the object commands are available throught the objects menu in MapInfo. MapBasic generally justs automates these.
r
On Mon, 31 May 2004 10:08:47 +1200, Apers Mathieu <[EMAIL PROTECTED]> wrote:
> ok so it won't let me attach Doc files either (or PDFs). i give up.
>
> -----Original Message-----
> From: Apers Mathieu [mailto:[EMAIL PROTECTED]
> Sent: Monday, 31 May 2004 10:07 AM
> To: 'Mapinfo help forum (E-mail)'
> Subject: RE: MI-L RE: Buffering query - v2
>
>
> Thanks to those of you who replied - unfortunately for me, i have no
> practical knowledge of Mapbasic and hence wouldn't have the foggiest
> idea of
> how to use Intersectnodes in Mapbasic, and i need seperate buffers for
> each
> object so "one buffer for all objects" wouldn't work either.
>
> See attached file:
>
> I would have thought there'd be a function that builds buffers like this,
> 'cause surely I'm not the only one who needs to buffer objects and have
> the
> buffers meet but not overlap???
>
> TIA
>
> Cheers
> Mathieu
>
>
>
>
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