[Openstreetmap-dev] Re: OSM Schema Design

Frank Mohr f_mohr at yahoo.de
Sun Jan 29 23:23:02 GMT 2006


M Josenhans wrote:
>>> rivers,
>>
>> Property "class=river" on a street could be a way to do this.
> 
> Looks quite wired to me. Property on a track would be better and street
> should be property of a track.

i think the idea was to keep the number of different "data types" low

street - everything that can be drawn as a line
node   - point
area   - as the name says

depending on the point of view, a river can also be a street
just look at the channels in Venice or Amsterdam

>>> lakes,
>>
>> Property "class=lake" on an area.
> 
> Looks better.
> But still there may be islands inside ;-)
> Maybe areas will need have other areas inside.

or as a overlay

>>> bridges,
>>
>> "class=bridge" on a line segment
> 
> OK.
> But here seems to become enhanced information required. If the bridge X
> of street A has been build cross street B, then it would be useful to
> associate that information with the map data.

Mainly which street if above the other
(did the "Frankfurter Kreuz" and "NW Kreuz Frankfurt" this weekend
and i'm still wondering how the layers should be done with level
information on the nodes)

>>> house numbers
>>
>> "house_number=xx" on a node
> 
> But the node must be somehow part of a street or have a reference to a
> street.
> Otherwise (e.g. at a crossing) its impossible to tell, to which street
> it belongs. Additional further information must be provided, to tell on
> which street-side the house is located.

on the line?
in germany this would be easy as even and odd house numbers are
om different sides

>>> railways,
>>
>> Property on a street
> 
> Looks quite wired to me.
> 
> A tram driving in the middle of a street would be a street in the middle
> of a street?

depends where the tram rails are
Looking at Darmstadt, most cases can be drawn by 3 "streets"
2 oneway for cars, one (or 2) for the tram line
in other cases, both lines overlap

>>> restrictions (max vehicle speed,
>>
>> Either property on a street or on a line segment
> 
> Property of one or more a directed line segments. Restrictions depend on
> the driving direction.

OK

>>> roundabouts,
> 
>  > Property on a node for small roundabouts or on several line segments for
> 
>> more complex ones. Maybe on a street which contain exactly all line
>> segments which participate on the roundabout.
> 
> Prefer property of a type 'roundabout' and of type street too. ;-)
> Connected to several tracks of type street. It might be worth to
> consider storing the angels at which the tracks arrive at the roundabout
> in order to have better maps for navigation.

that angle might be determined by the lines that connect

>>> country borders,
>>
>> Although I disbelieve this should be in an streetmap database, if you
>> want
>> to enter it, make it a property on a street surrounding the country.
> 
> Looks rather like a huge type of area me.

right ... but also with holes in it

>>> By the the way: unlike XML Schemes, which not only define the data
>>> structure, but also how the data is encoded, ASN.1 schemes just define
>>> how the data is structured and keep the data encoding separated to an
>>> appropriate encoder.
>>
>>
>> I think XML was not chosen because XML Schemes has to be used. XML was
>> chosen because it is the first and simplest idea that worked. Evidence to
>> this is, that no XML scheme validation is present anywhere in the code
>> now.
>>
>> If you know ASN.1 well  and if you point some ruby coders to ASN.1
>> libraries and define a ASN.1 scheme on how data are transfered
> 
> 
> Libraries with open source license are currently only available in C. I
> expect the effort build support for another language as high.

there are also Perl modules for ASN.1 and BER modules
(but i never tried them)

> I guess, that in encoding data the benefit of ASN.1 compared to XML is
> not so dramatic (factor 2), if you have an efficient XML parser, while
> in decoding the speed may be significant (factor 20). These numbers
> apply to using the ASN.1 BER encoder.

from memory i'd expect a faster encoding
(did't those ASN.1 compilers create ready to use encoding libraries
for a specific schema, while most XML libs create the encoding
schema at runtime?)

>> I never looked at ASN.1 more than I was forced to during study. 

same here

http://luca.ntop.org/Teaching/Appunti/asn1.html

helped me get througth that test

frank

	

	
		
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