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<body bgcolor="#FFFFFF" text="#000000"><div>Hi,</div><div><br></div><div>While reading this thread, I again stumbled upon the topic that QGIS is not able to handle arcs so far. Is that topic somehow also connect to the fact that each layer can only hold one type of geometry? </div><div><br></div><div>Cheers</div><div>Bernd</div><div><br></div><div><br></div><div><br></div><div>Am 04.04.2015, 10:28 Uhr, schrieb Marco Hugentobler <marco.hugentobler@sourcepole.ch>:<br></div><br><blockquote style="margin: 0 0 0.80ex; border-left: #0000FF 2px solid; padding-left: 1ex">
<div class="moz-cite-prefix">Hi<br>
<br>
Yes, the implicit assumption that each layer has one geometry type
probably goes back to the shapefile. I agree it is a wrong design
from QGIS to assume that and it is not in line with the logic of
many important datasources (Postgres, Oracle, MS SQL, WFS and also
some OGR formats like dxf), therefore causing workarounds on the
dataprovider level to seperate db tables into several layers. I
think it is best (at least in the long term) to have a logic
compatible to the datasources instead of doing workarounds at
provider and gui level.<br>
<br>
There are many places where this has an impact (e.g. symbology
system, editing). Therefore it will be good to break the 'one
geometry type' assumption not before version 3. A first step could
be to identify the places in core/gui/app where changes would be
needed.<br>
<br>
@Nathan and Victor: I don't have experience with MapInfo. What is
the exact reason why multi-geometries have been user-unfriendly
there?<br>
<br>
Regards,<br>
Marco<br>
<br>
<br>
<br>
On 02.04.2015 13:52, Olivier Dalang wrote:<br>
</div>
<blockquote cite="mid:CAExk7p2s6_waUrdU6P18_T1Y8L9BNL-o6Lu+o_Hi+Yct1t4LmA@mail.gmail.com" type="cite">
<div dir="ltr">
<div>Hi,</div>
<div><br>
</div>
<div>In some projects of mine, I work with multiple geometry
types in one postgis table, using a column of type <font style="background-color:rgb(238,238,238)" face="monospace,
monospace">geometry(Geometry,4326)</font>.</div>
<div>This is very well supported by postgis.</div>
<div><br>
</div>
<div>It is possible to load such a table in QGIS by manually
selecting the geometry type you want to load. This means that
to display all the features, you need to add the table three
times, one for each feature type.</div>
<div><br>
</div>
<div>This works more or less. There are a few bugs though :</div>
<div>- <a moz-do-not-send="true" href="http://hub.qgis.org/issues/12499">http://hub.qgis.org/issues/12499</a>
(you can edit other type's node with the node tool)</div>
<div>- <a moz-do-not-send="true" href="http://hub.qgis.org/issues/12500">http://hub.qgis.org/issues/12500</a>
(other type's records are shown in the attribute table)</div>
<div><br>
</div>
<div>This also has some limitations. When having such a setup,
it's pretty sure you'll want to have the same edit forms for
all the layers. You'll also probably want the same filter, the
same labels, the same actions, etc...</div>
<div>The only thing you'd want to be able to define on a
geometry type basis are the symbol (well, even the
classification/colors/etc could be shared) and the label
placement.</div>
<div>For now, you must do all settings three times, because of
this bug/feature request :</div>
<div>- <a moz-do-not-send="true" href="http://hub.qgis.org/issues/12303">http://hub.qgis.org/issues/12303</a>
(copy/paste style from one geometry type to another)</div>
<div><br>
</div>
<div><br>
</div>
<div>As you see, support multiple geometry types in QGIS is not
perfect.</div>
<div><br>
</div>
<div>Of course it's possible to fix the bugs/pr, and there are
some workarounds (postgis view instead of tables) but maybe
it's also worth thinking a bit more in depth about this.</div>
<div><br>
</div>
<div>We could consider point/line/polygons as
subcategories/sublayers of a layer. A shapefile or a
mono-typed table would have only one of those sublayer, but a
postgis table could perfectly have the three. Most of the
settings would be defined at the layer level, while only some
settings would be defined at the subcategory level.</div>
<div><br>
</div>
<div>This is probably especially relevant when thinking long
term (the day we support 3D, curves, etc...).</div>
<div><br>
</div>
<div><br>
</div>
<div>What do you think ?</div>
<div>Do you think the relation 1 layer = 1 geometry type will
hold ?</div>
<div><br>
</div>
<div>I think we inherited this from the old shapefile format,
but most data sources QGIS handles don't have this limitation.
I also think it does not hold with quite a lot of modern GIS
uses (especially web related, think of openstreetmaps for
instance).</div>
<div><br>
</div>
<div>There's this feature request (6th oldest open issue on the
tracker) about postgis geometry collections : <a moz-do-not-send="true" href="http://hub.qgis.org/issues/167">http://hub.qgis.org/issues/167</a></div>
<div><br>
</div>
<div><br>
</div>
<div>Best,</div>
<div><br>
</div>
<div>Olivier</div>
<div><br>
</div>
</div>
<br>
<br>
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</blockquote>
<br>
<br>
<pre class="moz-signature" cols="72">--
Dr. Marco Hugentobler
Sourcepole - Linux & Open Source Solutions
Weberstrasse 5, CH-8004 Zürich, Switzerland
<a class="moz-txt-link-abbreviated" href="mailto:marco.hugentobler@sourcepole.ch">marco.hugentobler@sourcepole.ch</a> <a class="moz-txt-link-freetext" href="http://www.sourcepole.ch">http://www.sourcepole.ch</a>
Technical Advisor QGIS Project Steering Committee </pre>
</blockquote><br><br><br><div id="M2Signature"><div>-- </div><div>Bernd Vogelgesang<br>Siedlerstraße 2<br>91083 Baiersdorf/Igelsdorf<br>Tel: 09133-825374</div></div></body></html>