clustering points

[Jan Hartmann]

See:

http://postgis.refractions.net/pipermail/postgis-users/2006-March/011324.html

Heinz-Josef Lücking wrote:
> Is the code of Schuyler available online or do i have to buy that book?
> 
> We where thinking about use of K-means for clustering too. Could you 
> pleae tell me more about the K-means-PostGIS-PostGres thing?
> 
> Heinz-Josef Lücking
> 
> Fawcett, David schrieb:
> 
>> You can see Schuyler's code working at:  
>> http://mappinghacks.com/projects/gmaps/cluster.html
>>
>> In the Google Maps Hacks book, Schuyler makes a pretty good case for 
>> why the tiling approach over K-means for on-the-fly mapping. 
>> That said, I know of one person doing K-means to cluster points.  This 
>> is implemented using PostGIS and Postgres-R.  Anyone, Bitner?!
>>
>> David.
>>
>> -----Original Message-----
>> From: UMN MapServer Users List [mailto:MAPSERVER-USERS at LISTS.UMN.EDU] 
>> On Behalf Of Schuyler Erle
>> Sent: Thursday, April 06, 2006 8:01 AM
>> To: MAPSERVER-USERS at LISTS.UMN.EDU
>> Subject: Re: [UMN_MAPSERVER-USERS] clustering points
>>
>>
>> * On  6-Apr-2006 at  2:57AM PDT, Heinz-Josef Lücking said:
>>
>>> I?m looking for a solution or hints on clustering points depending on
>>> distance. I would like to have just one symbol with diferent sizes 
>>> depending on how many points are "behind" that symbol.
>>
>>
>> I did some experiments with this for Google Maps Hacks, and I found 
>> that the fastest way to do this for a map display is to imagine a grid 
>> over your map view such that each cell would have the display size of 
>> your marker icon. Assign each of your points to the grid cell that 
>> contains it.  Finally, for each grid cell that contains a point, 
>> display a marker on the map for that cell. The marker can vary based 
>> on the number of points the cell contains.
>> SDE
>>
>