Well, I found many proposed solutions to my problem and just to let you all know,the concept I was asking for is : "Concave hull". Google search for it !
On Wed, May 5, 2010 at 5:28 PM, Oscar Zamudio <[email protected]> wrote: > Now that I get this polygon I found that it encloses all the streets in my > table and follows some more or less smooth path around them, much better > than a bounding box. But....to be honest, it is not the best suitable for my > purposes. I want a footprint of the whole bunch of streets. I mean: suppose > for a minute I have a table with only two equal length streets that crosses > each other at 90 degrees at the middle of them. With the proposed mechanism > I will get a square. > What I want to return from this cross is a closed cross shaped polygon that > sorrounds more or less smoothly the actual cross. Maybe I need to use some > buffer extent over the lines (to be defined) that helps to get the final > shape. This polygon is what I want to use as an area shape to query about > its overlaps with a point. > The need of such process is because I have many streets table for cities > that are closer to each other. Using bounding boxes concept they overlaps in > some regions for neighbour cities. This makes more complex the process of > finding to which city belongs a point that falls in the overlapping region. > Maybe a recursive process with dividing squares can be a good method. An > initial box that includes all the strets (extent) is divided in to four > squares. From these ones, the squares that contains streets (true) are left, > the other (false) are discarded. Every true square again is divided in 4 > subsquares and so on ..up to a minimum size of square (maybe 100 m x 100 > m). > I don't know if anyone has implemented or tried something like this or even > if there's already a solution to this problem. > Can anybody help me? > Thanks in advance, > > > On Wed, May 5, 2010 at 11:23 AM, Nicolas Ribot <[email protected]>wrote: > >> > Nicolas, >> > What I want to do is an insert of the type INSERT INTO...VALUES .. as >> > follows: >> > >> > INSERT INTO boundaries ( the_geom, the_name ) VALUES >> > (some_geometry_data,'some_arbitrary_name') >> > >> > My problem is that I want to replace the some_geometry_data value by the >> > result of the SELECT query. And of course I am not an expert user of SQL >> > statements so I don't know how to do that.. >> > from my_street_table; >> > Maybe your example can work, I will try it later and let you know. >> > >> > INSERT INTO boundaries ( the_geom, the_name ) SELECT >> > ST_ConvexHull(ST_Collect(the_geom)) as the_geom, 'mytablename' from >> > my_street_table; >> > >> >> So yes, the example, (or, better, the link to the INSERT command >> reference) will help you with the query. >> (When inserting with a SELECT, the VALUES keyword is not used). >> >> Nicolas >> _______________________________________________ >> postgis-users mailing list >> [email protected] >> http://postgis.refractions.net/mailman/listinfo/postgis-users >> > >
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