Re: decluttering

Hi Mark and Tennessee,

A couple of notes to the excellent explanation -

There is code in the Declutter matrix to make the size of the cells
bigger than 1x1 pixel. I haven't tested it, because I haven't had the
time and the DeclutterMatrix was designed for a customer that wanted
maps built off-line. Mark's code sounds like it effectively does the
same thing as increasing the size of the Matrix cell.

Ideally, Ken's response looks to be the best option for future growth in
this area. Joe Mark's studies look really interesting, and the results
are quite impressive in his papers, in terms of time and placement.

- Don

On Friday, July 6, 2001, at 11:19 AM, Mark Bucciarelli wrote:

> Hi Tennessee,
>
> Here's my recollection of how decluttering works. The display area
> is broken up into a big grid; this is the "matrix." When you ask
> the declutter matrix to place a label at a certain point, it calculates
> which cell grid the xy point falls into, and then looks up to see if
> this cell is already occupied. If it isn't, it returns the point
> and marks the cell as taken.
>
> If it is occupied, then things get more interesting. The program starts
> spiralling out from this point--picture a box centered at the point.
> This box has four sides and four corners. So in the first cycle, the
> algorithm looks at these eight cells. As soon as it finds an open cell,
> it marks it as used and returns a new point that is in that cell.
>
> If the first cycle doesn't find an open cell, it expands the "radius"
> of search and tries again. The FastDeclutterMatrix class drastically
> limits the number of cycles the algorithm performs.
>
> I think there are some other technical details like using font metrics
> to mark a bunch of cells for long labels and how the map decides on
> what the matrix cell size should be.
>
> Also, there is some commented out code in the library that allowed
> the graphic objects to take up cells. The BBN-NT developer thought
> it presumptuous to assume that a user would want graphics to use up
> grid cells as well as labels, as the map would get less label text
> this way.
>
> Hope that helps.
>
> --
> Mark Bucciarelli Peregrine Systems, Inc. R&D, Boston
> (413) 253-0020 mbucciarelli@peregrine.com Yahoo: m_bucciarelli
> http://www.peregrine.com
>
>> -----Original Message-----
>> From: Tennessee Leeuwenburg [mailto:t.leeuwenburg@bom.gov.au]
>> Sent: Thursday, July 05, 2001 9:19 PM
>> To: openmap-users@bbn.com
>> Subject: decluttering
>>
>>
>> Hi,
>>
>> I'm looking at the decluttering in openmap. It seems a bit
>> slow, even when
>> I don't have all that many data points. I was wondering how the
>> decluttering worked, and whether it would be worthwhile
>> trying to make the
>> algorithm a bit more efficient?
>>
>> -T
>> ==============================================
>> This email contains information which may be useful. The views
>> expressed within may or may not be the views of the author.
>> ==============================================
>>
>> -Tennessee Leeuwenburg, Silver Stream Pty Ltd
>> 0418 300 881
>>
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>
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