[Qgis-user] rant regarding "topology checkers"

[Zoltan]

Hi All,

The current thread with subject line "Re: [Qgis-user] Topology Checker 
Plugin" is a perfect example of my favourite Bee that lives in my bonnet.

Firstly a BIG +1 for open source is that you CAN look at the 
source-code, and there are a lot of people out there who are willing to 
give you an opinion based on their experience.

The big -1 for closed source is that the methodology of any button 
marked "Magically fix my data" is a closely guarded secret - so you have 
no idea what it is fixing or b*ggering up.

SO, people out there, KNOW your data.
It cannot be fixed (reliably) by someone who does not know what your 
data is trying to achieve.
For example: When is an overshoot a cul-du-sac and when is it an overshoot.
If the person writing the fix-up routine knows that your network is a 
water network, may it will be flagged as an overshoot. If they know it 
is a road network, maybe it is a cul-du-sac? But then, what if one of 
the roads is attributed as a freeway?

So, the best way to fix your data is to write the feature-relationships 
yourself, and to write (or run) the fixup scripts with the appropriate 
parameters when possible, or not run them (the 'canned' ones) at all, 
unless they give you a list of where to look, rather than quietly fixing 
it the way some programmer thinks it should be fixed.

AAAARGH!

OK, I'm quiet now.
End of rant.


Regards,
Zoltan
:-)


-- 

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Zoltan Szecsei PrGISc [PGP0031]
Geograph (Pty) Ltd.
GIS and Photogrammetric Services

P.O. Box 7, Muizenberg 7950, South Africa.

Mobile: +27-83-6004028
Fax:    +27-86-6115323   www.geograph.co.za
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