<br><br><div class="gmail_quote">On Tue, Mar 6, 2012 at 9:01 PM, Daniel Kastl <span dir="ltr"><<a href="mailto:daniel@georepublic.de">daniel@georepublic.de</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Hi Steve,<div><br></div><div>My answer probably isn't complete, but I hope others will add additional comments.</div><div>This is what I think could be improved:</div><div><ul><li>Driving Distance should have the possibility to return a polygon, but the "core" algorithm should just return a list of points that are within driving distance together with useful attributes as for example the cost to reach the point, or the previous point ID.<br>
<br></li><li>Currently it requires CGAL for the "alphashape" function. It would be nice, not to have CGAl as a dependency. With PostGIS 2.0 it's maybe possible to use ST_ConcaveHull instead. <br><a href="http://www.cgal.org/Manual/latest/doc_html/cgal_manual/Alpha_shapes_2/Chapter_main.html" target="_blank">http://www.cgal.org/Manual/latest/doc_html/cgal_manual/Alpha_shapes_2/Chapter_main.html</a></li>
</ul></div></blockquote><div>I've been using the points_as_polygon successfully. It would be nice to be able to have some ability to fine tune the alpha shape, but it does the job.</div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div><ul><li>For large networks it's a good idea to select only a small part (BBOX). This is easy as long as the cost attribute is in the same unit as the network data (ie. degree or meter). But if the cost is time for example, how to define a BBOX extent? If the BBOX is too small the driving distance area will look like the BBOX itself ;-) </li>
</ul></div></blockquote><div>My use case works with time (how far can I travel in <i>n</i> minutes). Streets/highways in the US rarely exceed 65mph/100kmph so I make my BBOX the size of the maximum possible distance that would be able to be traveled if all streets in all directions were the max speed.</div>
<div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div><ul>
</ul><div>Daniel</div><div><br></div><br><div class="gmail_quote"><div><div class="h5">On Wed, Mar 7, 2012 at 10:36 AM, Steve Horn <span dir="ltr"><steve@stevehorn.cc></span> wrote:<br></div></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div><div class="h5">
Hello list.
<div><br></div><div>I am interested in digging in more to the driving_distance functions to do some refining and perhaps improve the usefulness of the results (<a href="http://lists.osgeo.org/pipermail/pgrouting-dev/2012-February/000458.html" target="_blank">http://lists.osgeo.org/pipermail/pgrouting-dev/2012-February/000458.html</a>).</div>
<div><br></div><div>Having a hard time deciphering the current implementation, mostly because of my lack of familiarity with c/c++. Is there someone who wouldn't mind giving a synopsis of the overall approach that the algorithm takes?</div>
<div><br></div><div>Thanks!</div>
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