<br><br><div class="gmail_quote">On Tue, Apr 20, 2010 at 10:25 AM, G. Allegri <span dir="ltr"><<a href="mailto:giohappy@gmail.com">giohappy@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
<div class="im">> But even a simple overlay can give wrong results if the data is not<br>
> topologically clean... I personally cherish the fact that GRASS doesn't make<br>
> it easy to do things quick and dirty.<br>
<br>
</div>Probably we mean different things, or maybe I've msunderstood topology<br>
in Grass. Spatial operators like Overlay generally leaverages on<br>
topology graph structures (like in GEOS), but I suppsed that<br>
pseudo-topology (as meant in Grass) would be enough to guarantee the<br>
results. Isn't it?<br>
</blockquote></div><br>Most GRASS modules require information available in topology which might be true vector topology or other auxiliary information. This other auxiliary information also helps to make operations faster and safer, and BTW this is not a peculiarity of GRASS to require some auxiliary information. Reducing this info is in most cases not an option because it would sacrifice the accuracy of results. It remains unclear to me why you insist on reducing topological (true topological and other auxiliary) information gathering. Correct me if I'm wrong but AFAICT in GRASS there are equivalents to the SF algorithms you have in mind, IOW, in GRASS you can do everything you can do in e.g. SAGA, and a (fair) bit more. Many modules and functions already reduce the amount of topological information to the minimum required for the current operation, e.g. v.clean.<br>
<br>Replying to your next mail, both pseudo-topology and full topology are at feature level for all layers in a vector map.<br><br>Markus M<br>