That is so cool On Sat, May 8, 2010 at 11:30 PM, Jan Hartmann <[email protected]> wrote:
> How about this site? > > > http://www.johndcook.com/blog/2009/03/16/quasi-random-sequences-in-art-and-integration/ > > Jan > > > On 05/07/10 03:59, Ben Madin wrote: > >> Martin, >> >> Assuming you wanted feedback - from an epidemiologists perspective, I like >> the first one - Complete Spatial Randomness is an important concept to avoid >> engendering a perception of order or clustering, and I'm thinking as long as >> the relative 'dot-density' is correct for each polygon, the CSR approach is >> less like to lead people to think the dots are located on significant points >> - in the context of obscuring actual locations etc this is important. >> >> If you want it more regular, then maybe you don't need to randomise it - >> or maybe this just means the function needs a user parameter to be able to >> set the level of randomisation - From 0 (completely ordered) to 1 >> (completely Random) (... to 2.5 completely clustered?) >> >> Just my thoughts - also for my money, I wouldn't change dot sizes. very >> confusing. >> >> cheers >> >> Ben >> >> >> >> On 07/05/2010, at 6:11 , Martin Davis wrote: >> >> >> >>> Check out this blog post for some images of different kinds of random >>> point fields: >>> >>> >>> http://lin-ear-th-inking.blogspot.com/2010/05/more-random-points-in-jts.html >>> >>> Martin Davis wrote: >>> >>> >>>> Sounds like it could work - with maybe a bit of fiddling to deal with >>>> cases where the grid cells overlapped the polygon only slightly? >>>> Random perturbation by cell radius can still result in some points being >>>> very close together. (And I think this would also be an issue where only a >>>> small part of each grid cell overlapped the polygon). This may or may not >>>> be desirable. Perhaps a further check could be made to reduce the radius >>>> for points where this occurs. Or maybe some sort of simulated annealing >>>> process could be use to push the points into a more even distribution. >>>> >>>> M >>>> >>>> Paul Ramsey wrote: >>>> >>>> >>>>> Even-yet-random :) nice requirement. How about just starting with a >>>>> regular grid and then perturbing the elements randomly with a radius >>>>> of a cell size? You can use the area of the polygon and number of >>>>> needed points to calculate the appropriate cell size and go from >>>>> there. >>>>> >>>>> P >>>>> >>>>> On Thu, May 6, 2010 at 10:28 AM, Martin Davis<[email protected]> >>>>> wrote: >>>>> >>>>> >>>>> >>>>>> Good point about the need for even distribution of the points. That >>>>>> seems >>>>>> like a whole lot harder to code than simply randomly placing points in >>>>>> a >>>>>> polygon. Does anyone have any pointers to algorithms for producing >>>>>> this >>>>>> effect? >>>>>> >>>>>> George Silva wrote: >>>>>> >>>>>> >>>>>> >>>>>>> The really big problem with dot density is that dots can overlap >>>>>>> themselves, >>>>>>> masking the real number, so if anything will be developed in this >>>>>>> area, >>>>>>> the >>>>>>> points should be >>>>>>> >>>>>>> A) evenly distributed >>>>>>> or >>>>>>> B) randomly distributed, but with some sort of "colision" tests, so >>>>>>> there >>>>>>> is >>>>>>> no or little overlap. >>>>>>> >>>>>>> This is a interesting idea, especially if we could make a >>>>>>> materialized >>>>>>> view >>>>>>> with those points, which could be added to GIS software for >>>>>>> presentation. >>>>>>> >>>>>>> George >>>>>>> >>>>>>> On Thu, May 6, 2010 at 1:53 PM, Sufficool, Stanley< >>>>>>> [email protected]> wrote: >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>>> Looks nasty, but it might work: >>>>>>>> >>>>>>>> select >>>>>>>> st_line_interpolate_point( >>>>>>>> st_intersection( >>>>>>>> the_geom, >>>>>>>> st_makeline( >>>>>>>> st_pointn(st_exteriorring(the_geom), >>>>>>>> (rand1.rand * >>>>>>>> st_npoints(st_exteriorring(the_geom)))::int), >>>>>>>> st_pointn(st_exteriorring(the_geom), >>>>>>>> (rand2.rand * >>>>>>>> st_npoints(st_exteriorring(the_geom)))::int) >>>>>>>> ) >>>>>>>> ) >>>>>>>> ,rand3.rand >>>>>>>> ) >>>>>>>> from insert_your_table_name_here, >>>>>>>> (select random() as rand, generate_series(1,1000) as point_number) >>>>>>>> as >>>>>>>> rand1 >>>>>>>> JOIN (select random() as rand, generate_series(1,1000) as >>>>>>>> point_number) >>>>>>>> as >>>>>>>> rand2 >>>>>>>> ON rand1.point_number = rand2.point_number >>>>>>>> JOIN (select random() as rand, generate_series(1,1000) as >>>>>>>> point_number) >>>>>>>> as >>>>>>>> rand3 >>>>>>>> ON rand2.point_number = rand3.point_number >>>>>>>> WHERE st_geometrytype( >>>>>>>> st_intersection( >>>>>>>> the_geom, >>>>>>>> st_makeline( >>>>>>>> st_pointn(st_exteriorring(the_geom), >>>>>>>> (rand1.rand * >>>>>>>> st_npoints(st_exteriorring(the_geom)))::int), >>>>>>>> st_pointn(st_exteriorring(the_geom), >>>>>>>> (rand2.rand * >>>>>>>> st_npoints(st_exteriorring(the_geom)))::int) >>>>>>>> ) >>>>>>>> ) >>>>>>>> ) = 'ST_LineString' >>>>>>>> AND oid = 5030 /* Enter your own OID here */ >>>>>>>> limit 100 >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>>> -----Original Message----- >>>>>>>>> From: [email protected] >>>>>>>>> [mailto:[email protected]] On >>>>>>>>> Behalf Of Martin Davis >>>>>>>>> Sent: Thursday, May 06, 2010 8:56 AM >>>>>>>>> To: John Abraham; [email protected]; Martin >>>>>>>>> Davis >>>>>>>>> Subject: Re: [postgis-users] Dot Density idea >>>>>>>>> >>>>>>>>> >>>>>>>>> I was thinking the same thing! >>>>>>>>> >>>>>>>>> strk wrote: >>>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>>>> ST_RandomPoinsOnSurface(geometry, numpoints) would be an >>>>>>>>>> interesting >>>>>>>>>> function indeed. Sounds like a good job for GEOS/JTS. >>>>>>>>>> >>>>>>>>>> --strk; >>>>>>>>>> >>>>>>>>>> On Mon, May 03, 2010 at 10:49:32PM -0600, John Abraham wrote: >>>>>>>>>> >>>>>>>>>> >>>>>>>>>> >>>>>>>>>> >>>>>>>>>> >>>>>>>>>>> One of the things I miss about using ESRI's GIS is the >>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>> ability to do >>>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>>>> dot-density maps. Within a polygon, the number of dots is >>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>> proportional to a value, and the dots are randomly placed. I >>>>>>>>> find it useful to be able to present several data values at >>>>>>>>> once (e.g. blue dots for population, red dots for employment). >>>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>>>> I also find that it is a more intuitive way of scaling for >>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>> zone size >>>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>>>> than dividing the value by the area of the zone. That is, >>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>> the count >>>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>>>> of the dots represents the actual number, but the density >>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>> of the dots >>>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>>>> represents the density of the number. So I don't have to decide >>>>>>>>>>> whether to divide the value by the area of the polygon to plot >>>>>>>>>>> density: both the absolute number and the density are >>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>> easily visible. >>>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>>>> Since my open-source GIS viewing systems (mostly QGIS and >>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>> Mapserver) >>>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>>>> won't plot dot-density, I've done without. >>>>>>>>>>> >>>>>>>>>>> But today I realized that I can build these on the server >>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>> instead. I >>>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>>>> can generate random points within the bounding-box of the polygon, >>>>>>>>>>> throwing out those that aren't contained within the polygon, >>>>>>>>>>> repeating until I have enough. Then I can save these points as a >>>>>>>>>>> separate layer, and display this layer using almost any desktop >>>>>>>>>>> or >>>>>>>>>>> web based viewer! >>>>>>>>>>> >>>>>>>>>>> Has anyone done this? Can I do it in SQL or do I need to write >>>>>>>>>>> something in PL/pgsql? >>>>>>>>>>> >>>>>>>>>>> -- >>>>>>>>>>> John Abraham >>>>>>>>>>> >>>>>>>>>>> PS I just bought the Postgis In Action book; enjoying it so far. >>>>>>>>>>> _______________________________________________ >>>>>>>>>>> postgis-users mailing list [email protected] >>>>>>>>>>> http://postgis.refractions.net/mailman/listinfo/postgis-users >>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>> >>>>>>>>>> >>>>>>>>>> >>>>>>>>> -- >>>>>>>>> Martin Davis >>>>>>>>> Senior Technical Architect >>>>>>>>> Refractions Research, Inc. >>>>>>>>> (250) 383-3022 >>>>>>>>> >>>>>>>>> _______________________________________________ >>>>>>>>> postgis-users mailing list >>>>>>>>> [email protected] >>>>>>>>> http://postgis.refractions.net/mailman/listinfo/postgis-users >>>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>> _______________________________________________ >>>>>>>> postgis-users mailing list >>>>>>>> [email protected] >>>>>>>> http://postgis.refractions.net/mailman/listinfo/postgis-users >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>> >>>>>>> ------------------------------------------------------------------------ >>>>>>> >>>>>>> _______________________________________________ >>>>>>> postgis-users mailing list >>>>>>> [email protected] >>>>>>> http://postgis.refractions.net/mailman/listinfo/postgis-users >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>> -- >>>>>> Martin Davis >>>>>> Senior Technical Architect >>>>>> Refractions Research, Inc. >>>>>> (250) 383-3022 >>>>>> >>>>>> _______________________________________________ >>>>>> postgis-users mailing list >>>>>> [email protected] >>>>>> http://postgis.refractions.net/mailman/listinfo/postgis-users >>>>>> >>>>>> >>>>>> >>>>>> >>>>> _______________________________________________ >>>>> postgis-users mailing list >>>>> [email protected] >>>>> http://postgis.refractions.net/mailman/listinfo/postgis-users >>>>> >>>>> >>>>> >>>>> >>>> >>>> >>> -- >>> Martin Davis >>> Senior Technical Architect >>> Refractions Research, Inc. >>> (250) 383-3022 >>> >>> _______________________________________________ >>> postgis-users mailing list >>> [email protected] >>> http://postgis.refractions.net/mailman/listinfo/postgis-users >>> >>> >> _______________________________________________ >> postgis-users mailing list >> [email protected] >> http://postgis.refractions.net/mailman/listinfo/postgis-users >> >> > _______________________________________________ > postgis-users mailing list > [email protected] > http://postgis.refractions.net/mailman/listinfo/postgis-users >
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