Bill,
Thanks for the ideas. I might try to do something with the viewshed idea
in the future. It would need a LOT of computing to process all the road
segments in a National dataset like Tiger.
But for now I would like to figure out the routing costs.
One idea I had was to compute the grade for a segment and then compute
cost as:
cost = (time or distance) * scalefactor * max(abs(grade), 1.0)
This would have the effect of causing segments with a lot of grade to
have a higher cost of traversal.
Or similarly, if you want to pick roads with a lot of elevation changes
then use cost factor like:
cost = (time or distance) * scalefactor /
abs(sum_elevation_changes_over_the_segment)
This would have the effect of decreasing the traversal cost for segments
that have a lot of elevation changes.
These are pretty crude estimates and probably would need some fine
tuning to get reasonable results.
Thanks,
-Steve W
On 9/13/2010 4:24 PM, Bill Thoen wrote:
Stephen Woodbridge wrote:
Hi all,
(This is cross posting from the pgrouting list, sorry for the dups.)
I have preprocessed some shapefile data and added elevation
information in the Z value of the coordinates. I'm wondering how to
best utilize that in routes and would like any thoughts or ideas you
might be willing to share.
The obvious answer is to wrap the elevation data into the cost values
as this is simple and straight forward and does not require code
changes. This brings me to what have other people done or thought
about doing in this regard?
Since you seem to enjoy large database problems, have you considered
loading the DEM data together with the roads and sample the viewshed
every few km? You could then create an objective cost factor for
"scenic," proportional to the amount of land visible, with some
adjusting factor that distinguishes morphology, land cover, or other
weighted factors from each sample point. Creating a scale of "scenic"
and "picturesque" as it goes form "ho-hum flatland" to "precipitous,
brake-burning, wheel-gripping adventurous" might be fun all by itself.
If you're looking for 3D ideas, there's a GIS consulting company across
the hall from me that specializes in 3D information, visualization and
analysis, and I know they are working on web services to deliver the
sort of data that an application like yours would consume. Their website
is full of 3D imagery, articles and examples that you might want to
check out for ideas or inspiration There's a particularly good
demonstration of using fog instead of shadow to create a visual
representation of ridge lines, if your 're using those to determine a
topographic index (see http://ctmap.com/serendipity/index.php).
*Bill Thoen*
GISnet - www.gisnet.com <http://www.gisnet.com/>
1401 Walnut St., Suite C
Boulder, CO 80302
303-786-9961 tel
303-443-4856 fax
bth...@gisnet.com
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