[OSM-dev] Polygons in OSM don't necessarily comply to simple feature specification

Frederik Ramm frederik at remote.org
Wed Apr 16 23:07:29 BST 2008


Hi,

> yesterday a colleague approached me asking why OSM data
> doesn't comply to the Simple Feature specification[1]

I guess the honest answer is very likely that most people invovled in
designing anything at OSM have no prior GIS experience. Most of us are
amateurs. We design stuff that we think works, and if people say we
don't follow standards then we say that's by design, but mostly it is
just ignorance. 

And ignorance is bliss. 

I had to read a couple OGC(*) standards in the past. It begins with
selecting wether you want the 0.7 or the 1.0 or the 1.1.0 version, the
Implementation Specification or the Implementation Specfication
Corrigendum or the Implementation Specification Havum Coolum Wordum
document. Then you are invited to read a page of small print that you
have to accept before they even tell you what the standard is they
would like you to implement. After that you get a document which more
or less reads like a Chomsky book on transformation grammar, only
where Chomsky used short words and letters to identify elements, they
usually have sentences. So make extra sure you don't confuse the
Server Answer Receipt Message Confirmation with the Server Answer
Recepit Message Confirmation Request because both are, cleary, very
different things. 

I'm overdoing it a bit here, but only a bit. The most difficult part
for me is distingushing between those parts of these documents which
are really the bread-and-butter stuff that any software worth its
salt must support, and which parts are just fancy cloud cuckoo stuff
that nobody even attempted to support.

If the OGC material was more accessible - I'm not asking much, I'd
just like Internet RfC style with a few examples every now and then or
something like that - then I'm sure more Open Source developers would
actually take the time to try and implement stuff conforming to their
specs. But the way these specs currently worded and delivered gives
the impression that they're not very interested - sometimes I think it
is enough for them if their paying members understand what is meant
(because their paying members have been involved in the mailing lists
and working groups and don't need to read the actual paper that comes
out at the end).

So much for OGC stuff in general. About Simple Features specifically,
I guess there simply was nobody who wanted to do the extra work. I
remember Artem complaining about self-intersecting stuff once and I
think the offending items are sorted out somewhere in osm2pgsql, are
they not?

Bye
Frederik

(*) The number is not high enough for my findings to be statistically
    significant.

-- 
Frederik Ramm  ##  eMail frederik at remote.org  ##  N49°00'09" E008°23'33"





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