Chopping a map with a grid.

[David William Bitner]

I am not sure of any mapscript approaches for this type of problem.  I
currently do this to create a grid that shows how many flights cross a given
grid cell in my application at http://maps.macnoise.com/interactive/ (select
flight tracks grid from the layer list) using postgis.

The general approach that I have is to either use a pre-built grid or a
plpgsql function that builds the grid on the fly and to create a layer in
mapserver that does an on the fly intersection between the two with a data
statement similar to this:

DATA "the_geom from (select count(f.id) as count, g.geom as the_geom from
grid as g,flighttracks as f where g.geom && f.geom and crosses(g.geom,f.geom))
using unique the_geom using srid=-1"

David



On 1/26/07, Rodrigo Del C. Andrade <rodrigo.andrade at digitro.com.br> wrote:
>
>
>     Hi dear list.
>
>     I am trying to implement in java mapscript an application that draws
> on-the-fly contours around areas with a high ocurrence rate of a given
> event, something like the topics discussed in here:
> http://article.gmane.org/gmane.comp.gis.mapserver.user/17924.
>     I understand it is not easy, so I am taking my steps one at a time.
> Being quite new to GIS programming, I am going trough the usual misteps.
>
>     My first problem is actually dividing the area into subzones where I
> can count the ocurrences of said events inside each rectangle to feed the
> statistic analysis. I have tried using a graticule item on a line layer, but
> I cant seem to find a query method that will give me something I can work
> with (boundaries, polygons, the works), even though the grid has been drawn
> quite nicelly.
>     I understand I probably missed completelly the point of a GRID object
> inside a LINE type layer, but is there some built in way (trough grid or any
> other method) to chop a layer in equal rectangles so I can iterate trough
> each of them checking for ocorrences?
>
>     Thanks a lot.
>
> --
>
>
> *Rodrigo Del C. Andrade*
> *Estagiário Nível Superior*
> *SIC - SSE - Soluções Segurança Pública*
>
> *DÍGITRO TECNOLOGIA*
> *E-mail:* rodrigo.andrade at digitro.com.br
> *Fone:* +55 48 3281-7390 / +55 48 3281-7000
> *Fax:* +55 48 3281-7299
> *Site:* www.digitro.com
>



-- 
************************************
David William Bitner
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