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<div class="moz-cite-prefix">On 2012/10/30 16:13, Burgstaller Stefan
wrote:<br>
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<div class="WordSection1">
<p class="MsoNormal"><span lang="EN-US">@Zoltan:<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">I will explain my
problem now in detail since I think that this problem could
be known to a lot of users:<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">In Germany we can order
cadastre data in a proprietary format from our land
surveying offices. To be able to use this proprietary ASCII
format with common GIS software we convert the geometry
objects with corresponding data into point-, line- and
polygon-shapes. Unfortunately the source to convert contains
different errors like unclosed polygons (start and end
coordinates are not the same), null geometries, incorrect
ring ordering, duplicate vertex or self intersections, which
are not repaired by the converting tool and therefore lead
to errors in the shape files. When I want to use these
shapefiles later for spatial functions like a select by
location with calculating intersections based on one of
these error-shapes, the results can be wrong due to the
errors named above. Until now I did not find any software
function to solve these problems “smart” with a few clicks
except for the geometry repair functions provided by ArcGIS.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Even the GRASS v.clean
function will not solve the problems listed above.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:DE"
lang="EN-US">Greetings,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:DE"
lang="EN-US"> <o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:DE"
lang="EN-US">Stefan Burgstaller<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
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Hi Stefan,<br>
We have the same issues in South Africa with our Land Survey data.<br>
I went a long way to cleaning the data by writing C code to check
and log, or repair and log the source data as I converted/cleaned it
for a client.<br>
This was about 7 years ago.<br>
<br>
I'm guessing when you get updates to the cadastre, you get the whole
data set again, so you have a repeat-cleaning cycle.<br>
<br>
In my opinion the only way to handle this is with custom code.<br>
Take each land parcel and if it seems clean, pass it through.<br>
Then look at the left overs to see if you can find a common thread
of errors, program that, and re run to get a new set of leftovers.<br>
Once that is done, you can start looking at the relative positions
and uses (road widening or land parcel) and start figuring out the
slivers and overlaps and other issues.<br>
<br>
It is not as simple as I make it out to be, but it is the only way
to protect your data from being too unreliable, and to stop you
having to manually redo all the work again, for every update you
get.<br>
It's a big effort, but well worth it if you are the only one with a
clean data-set :-)<br>
<br>
I am likely to be out of office quite a lot for the next 4-6 weeks,
otherwise I would ask you for a sample to see if I could offer
better guidance.<br>
<br>
Let me know how you go - and how you end up solving it.<br>
<br>
Good luck and kind regards,<br>
Zoltan<br>
<br>
<pre class="moz-signature" cols="72">--
===========================================
Zoltan Szecsei PrGISc [PGP0031]
Geograph (Pty) Ltd.
P.O. Box 7, Muizenberg 7950, South Africa.
65 Main Road, Muizenberg 7945
Western Cape, South Africa.
34° 6'16.35"S 18°28'5.62"E
Tel: +27-21-7884897 Mobile: +27-83-6004028
Fax: +27-86-6115323 <a class="moz-txt-link-abbreviated" href="http://www.geograph.co.za">www.geograph.co.za</a>
===========================================</pre>
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