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Subject: Re: [geometry] Using Boost.Geometry with a legacy class hierarchy
From: Barend Gehrels (barend_at_[hidden])
Date: 2012-02-12 11:11:48

Hi Mats,

>>> I think I've managed to adapt QPoint and QLineString, because the
>>> result of the program is a correct WKT. However, if there are better
>>> ways of defining a boost range for this purpose, I would love to
>>> hear about it. (None of my functions are named "range_value", and
>>> since the documentation states "The type defined by the metafunction
>>> |range_value<...>::type| must fulfill the Point Concept
>>> <>",
>>> I guess there is a better way...?)
>> OK I see. Notice also
>> ...\libs\geometry\example\with_external_libs\x06_qt_world_mapper.cpp
>> and x01_qt_example.cpp in the same folder, but maybe you did already.
>> As far as I can see this is correct. I did not compile it but you
>> have done.
>> The range_value meta-function is (AFAIK) automatically provided, as
>> long as you adapt it properly to the range concept, and so to see you
>> did. Maybe we should include that in the docs.
> I see. :) Perhaps provide a link in the Boost.Geometry docs to e.g.
> the example I used in the Boost.Range docs as well?

A link to the page in Boost.Range is added.

Note that the range_value statement is correct in the docs. It states
that the type defined by range_value should fulfill the point concept.
It does not state that range_value has to be provided.

I can add your sample but as it is it is already in an example, in
another way. That might be confusing. So for the moment (deadline
happens to be tomorrow) I'll wait with that. Thanks.

>>> The next step is to adapt the QRing class. I need to create a single
>>> iterator sequence that loops all of the linestrings contained in the
>>> QRing::lines directly, but -- especially since I'm not sure if the
>>> boost.range part of QLineString is done correctly -- I don't know
>>> the right way to do it. Could you give me any pointers?
>> So the linestring is done correctly, and the ring gets, in general,
>> an equal implementation because they are similar w.r.t. ranges etc.
>> What I don't understand is looping over linestrings contain in
>> QRing::lines. But maybe I don't understand QRing::lines well.
>> Basically Boost.Geometry's ring is a vector of points, which happen
>> to form a closed polygon (without holes). So it is similar to a
>> linestring.
> You are correct -- my legacy class hierarchy is laid out to maintain
> the topology/shared geometry, which does not fit seamlessly into the
> Boost.Geometry model. (You might recall discussion on this list a
> while back.) Therefore, I will need to create an iterator that loops
> over every linestring (and the linestring's points) in QRing::lines,
> that masks as a single collection of points. Do you know how (and if)
> I could achieve that somehow?

Ah, now I remember, sorry. Yest that must be possible, but I've never
tried this. So I currently cannot give you links how to do this. The
challenge is to make an iterator properly walking over the various

Regards, Barend

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