[postgis-users] Elevation Profiles

[strk at refractions.net]

I think you need to extend postgis for that.
An elevate(geometry, grid) would be nice to have.

--strk;

On Wed, Nov 24, 2004 at 11:46:31AM -0700, ANDREW WOOLEY wrote:
> Folks,
> 
> I have been working on this idea for some time and have been trying to
> implement elevation profiles and have yet to get it working like I want.
>  I am hoping that someone has some good ideas for me.
> 
> Here is my problem. I have a series of lines in a table.  I also have a
> table with elevations as polygons. I overlay them using this query:
> select e.gridcode as elevation from mtntrails_elevation as e, route as
> r where e.the_geom && r.the_geom; 
> (route has one trail with 3 or 4 segments.)(mtntrails_elevation has ~7
> million rows.)
> 
> This query works. It pulls out elevations where they overlap the trail.
>  However, when I list out the elevations, they don't seem to be in the
> "correct" order - that is the order I think they should be in.  The way
> that I hope/imagine this happens is that it will select based on
> coordinates of the vertices in the line. However, it seems that they are
> selected all at once in no particular order. By order I mean I want the
> polygons in the elevation table to be selected in spatial order from the
> start of the trail to the end of the trail.
> 
> Is there a better way to go about this?  I have tried to collect() the
> trail segments, but that doesn't seem to help. Is there something wrong
> with my basic premise?  I have thought about breaking up the line into
> vertices and looping through each one and selecting that way, but that
> seems unnecessarily difficult.  
> 
> Any ideas?
> 
> Thanks.
> 
> Andrew Wooley
> GIS Coordinator
> Mountainland Association of Governments
> 586 E 800 N
> Orem, UT 84097
> ph: 801.229.3844
> email: awooley at mountainland.org
> web: http://maps.mountainland.org
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