I am on alert about local wildfires, so I will not type up a large discussion of hulls, but if you generate a selection mask image (zero outside the selection, one inside it) then the obvious thing to use is either "do_something_to($source->where($mask));" if you don't need to track the coordinates themselves, or "$dex = $mask->whichND; do_something_to($source->indexND($dex));" if you do.
On Sep 7, 2010, at 7:31 PM, P Kishor wrote: > Rectangular selections from 2D piddles are easy and fast with the > range operator. However, I would like to grab a non-rectangular > selection out of a piddle, setting all out-of-area-of-interest > elements to BAD. > > Background -- > > - The user clicks on a map and creates an irregular polygon > - I (somehow **) figure out the piddle elements, aka cells, that lie > within the drawn poly > - Out of the base piddle, I grab the tightest rect that contains the > cells within the drawn poly (the min. bounding box) > - Set all the cells outside the drawn poly to BAD so they don't figure > in the rest of the calculations > > I searched the docs, but the closest discussion I found was on > convex-hulls from June 2005 [1]. Suggestions? > > ** the reason I say "somehow" is because I can do a lookup using a > database to get the indices of the mouse-clicks, and the elements that > lie within the bounding rect, but I would prefer to do this without a > database. I am generally finding PDL to be substantively faster than a > database, and would like to stay out of a db as much as possible. I > initiated a discussion on this a while back, but that was restricted > to rectangular selects. > > [1] http://mailman.jach.hawaii.edu/pipermail/perldl/2005-June/000036.html > > -- > Puneet Kishor http://www.punkish.org > Carbon Model http://carbonmodel.org > Charter Member, Open Source Geospatial Foundation http://www.osgeo.org > Science Commons Fellow, http://sciencecommons.org/about/whoweare/ > kishor > Nelson Institute, UW-Madison http://www.nelson.wisc.edu > ----------------------------------------------------------------------- > Assertions are politics; backing up assertions with evidence is > science > = > ====================================================================== > > _______________________________________________ > Perldl mailing list > [email protected] > http://mailman.jach.hawaii.edu/mailman/listinfo/perldl > _______________________________________________ Perldl mailing list [email protected] http://mailman.jach.hawaii.edu/mailman/listinfo/perldl
