[postgis-users] Elevation Profiles

[ANDREW WOOLEY]

Thanks for the reply. That sounds like it would be a nice solution. I am
not sure that my methods are correct.  How does software like Topo! or
many of the other similar products generate profiles?  They do it so
quickly and with small data files.  I am using DEM data, but is there
something else that will work better? Is there any documentation that
will teach me the right way to do this?

Andrew

>>> strk at refractions.net 11/24/2004 11:50:34 AM >>>
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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