Hi David,<br><br>Deleting duplicates that are only different in the cat column would definitely be possible with SQL, but I don't know enough SQL to give you a quick command for that. I think the relevant command would be v.extract.<br>
<br>Other than that, GRASS does have many fundamental differences compared to other GIS - for example, that vectors are attached to tables, but not in the sense that one entry in the table necessarily means one vector feature. Features can e.g. be attached to several tables simultaneously, something that is also possible with other GIS but functions differently. A good description of the GRASS vector model is available here:<br>
<a href="http://grass.osgeo.org/gdp/html_grass63/vectorintro.html">http://grass.osgeo.org/gdp/html_grass63/vectorintro.html</a><br><br>Hope that helps at least a little bit :)<br>Daniel<br clear="all">
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px"><span style="font-family:arial,sans-serif;font-size:13px;background-color:rgb(255,255,255)"></span></p><p>--<br></p><p>B.Sc. Daniel Lee<br>
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Zusätzliche Unterstützung erhält ISIS von dem Entrepreneurship Cluster Mittelhessen, der Universität Marburg, dem Laboratory for Climatology and Remote Sensing und dem GIS-Lab Marburg.</p><p></p><br>
<br><br><div class="gmail_quote">Am 2. April 2012 21:09 schrieb David J. Bakeman <span dir="ltr"><<a href="mailto:dbakeman@comcast.net">dbakeman@comcast.net</a>></span>:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div class="HOEnZb"><div class="h5">Markus Metz wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
On Sun, Apr 1, 2012 at 11:45 PM, David J. Bakeman<<a href="mailto:dbakeman@comcast.net" target="_blank">dbakeman@comcast.net</a>> wrote:<br>
<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
David J. Bakeman wrote:<br>
<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Markus Neteler wrote:<br>
<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
On Sun, Apr 1, 2012 at 9:45 PM, David J. Bakeman<<a href="mailto:dbakeman@comcast.net" target="_blank">dbakeman@comcast.net</a>><br>
wrote:<br>
<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
I didn't find an answer in the archives so.<br>
<br>
I have a shapefile of polygons and some of the polygons are duplicated.<br>
I<br>
thought I could use v.clean tool=rmdupl to get rid of these polygons. I<br>
use<br>
v.in.ogr to read it in and I get the following:<br>
<br>
WARNING: 8 areas represent more (overlapping) features, because polygons<br>
overlap in input layer(s). Such areas are linked to more than 1<br>
row in attribute table. The number of features for those areas<br>
is<br>
stored as category in layer 2<br>
<br>
That is correct in that there are 8 duplicate polygons but the only<br>
different attribute is the cat which grass added? What am I missing? I<br>
then tried v.clean tool=bpol,rmdupl and nothing changes it still has the<br>
8<br>
duplicates. What am I doing wrong?<br>
<br>
</blockquote>
I think that you need to add the break tool for v.clean.<br>
<br>
</blockquote>
Correct that was actually what I was using: v.clean tool=break,rmdupl<br>
<br>
Looking closer I see that when I run v.clean it doesn't even report the<br>
duplicates that v.in.ogr did but they are still there. The only thing that<br>
differs in coordinates or attributes is the cat attribute that grass added.<br>
<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
I am using grass 6.3.0 on fedora core 14 linux.<br>
<br>
</blockquote>
Please note that you can upgrade to grass-6.4.0-4.fc14:<br>
<a href="http://koji.fedoraproject.org/koji/buildinfo?buildID=263115" target="_blank">http://koji.fedoraproject.org/<u></u>koji/buildinfo?buildID=263115</a><br>
<br>
</blockquote>
Thanks I'll see if I can upgrade.<br>
<br>
</blockquote>
I upgraded to the 6.4.0 and the results are exactly the same. The polygons<br>
really are identical in every respect except for they have different values<br>
in the cat column. Is there some other grass tool for removing this kind of<br>
duplicate?<br>
<br>
</blockquote>
After import with v.in.ogr, there are no duplicate geometries left in<br>
the vector. What you have now is some areas with two categories<br>
assigned to them. Removing the duplicates means in this case removing<br>
one of the two categories, for example with one of the vector<br>
digitizers.<br>
<br>
</blockquote></div></div>
I'm relatively new to grass but that doesn't make sense. I started with a shapefile with duplicate features. That is polygons with the exact same attributes and geometry (they are identical). What I thought grass could do for me was to read it in and delete one of the duplicates without user intervention. After all it identifies the duplicates so why can't it delete one?<br>
<br>
Are you saying that the duplicate geometry was deleted but it kept both rows even though they were identical as well? Is there a operation that would identify and delete rows that differ in only the cat attribute.<div class="HOEnZb">
<div class="h5"><br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Markus M<br>
<br>
<br>
</blockquote>
<br>
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