[postgis-users] Simple Line Density

[Karl Zinglersen]

Hi Pierre,
Thanks for the link to the add-on and the sql statements.

Karl

Den onsdag den 27. november 2013 14.21.46 UTC-3 skrev Pierre Racine:
>
> Hi Karl, 
>
> I do this with the ST_ExtractToRaster() function from the PostGIS Add-ons: 
>
> https://github.com/pedrogit/postgisaddons/releases/tag/1.21 
>
> I just added a SUM_OF_LENGTHS method to ST_ExtractToRaster(). 
>
> Look at the ST_ExtractToRaster() function in the postgis_addons.sql file 
> for an example. In your case it should look like this: 
>
> SELECT ST_ExtractToRaster(ST_AddBand(ST_MakeEmptyRaster(rast), '32BF'), 
> 'public', 'geomtable', 'geom', null, 'SUM_OF_LENGTHS') rast 
> FROM refrastertable; 
>
> You should have a reference raster already existing in a table and your 
> lines should be indexed. 
>
> Pierre 
>
> > -----Original Message----- 
> > From: postgis-us... at lists.osgeo.org <javascript:> [mailto:postgis-users-<javascript:> 
> > bou... at lists.osgeo.org <javascript:>] On Behalf Of Karl Zinglersen 
> > Sent: Wednesday, November 27, 2013 11:30 AM 
> > To: postgi... at googlegroups.com <javascript:> 
> > Cc: PostGIS Users Discussion 
> > Subject: Re: [postgis-users] Simple Line Density 
> > 
> > Hi, 
> > I am dealing with the same types of data and issues as Jeff. 
> > My procedure for data clean up is: 
> > 1) CSV files into PostGIS as points 
> > 1.1) ST_TRANSFORM to projected spatial reference (here EPSG:32621 / 
> > UTM zone 21 N WGS84) 
> > 2) ST_MAKELINE to "sub"-lines via PARTITION BY 
> > 3) Create a gridded polygon layer in same srid 
> > 4) Run equivalent to select cell_id, line_id from cells, lines where 
> > intersects(lines.geom, cells.geom 
> > - but my postgis runs out of memory after a while. And I am sorry to say 
> > Spatial Analyst doesn't. 
> > Is there more memory cheap way to do it in PostGIS (e.g. via the raster 
> > functions - although I haven't found i yet). 
> > 
> > Karl 
> > 
> > Den onsdag den 26. december 2012 09.58.43 UTC-3 skrev Jeff Adams - 
> > NOAA Affiliate: 
> > 
> >         Hi Brent, 
> > 
> >         Thanks for the response. I don't think your original response 
> made 
> > it into my inbox via the list, but now I see it on the website thread. 
> That 
> > seems like it might be a viable alternative, I just worry about those 
> vessel 
> > tracks that would be clearly outside of a particular grid cell, but 
> whose 
> > buffer would bleed over. How did you handle this type of situation? 
> > 
> >         Jeff 
> > 
> > 
> >         On Mon, Dec 24, 2012 at 7:22 PM, <pcr... at pcreso.com 
> > <javascript:> > wrote: 
> > 
> > 
> > Jeff, 
> > 
> > Did you see my reply using vessel tracklines as vectors & a grid in 
> Postgis to 
> > do exactly what you describe? 
> > 
> > Given we were looking at benthic impact, we buffered the tracklines to 
> > create polygons representing the swept area of the deployed fishing 
> gear. 
> > These were clipped by the cells, & we could generate statistics suca as 
> the 
> > cumulative swept area of all tracks with each cell, number of times each 
> cell 
> > was crossed, & given the tracklines have a timestamp associated with 
> them, 
> > we could also look at the temporal pattern of tracks crossing cells, for 
> > things like seasonal impacts & variation between seasons. 
> > 
> > Cheers, 
> > 
> >   Brent Wood 
> > 
>
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