Geometry Boost List: Re: [geometry] Using Boost.Geometry with a legacy class hierarchy

Subject: Re: [geometry] Using Boost.Geometry with a legacy class hierarchy
From: Mats Taraldsvik (mats.taraldsvik_at_[hidden])
Date: 2012-02-17 06:10:29

Hi,

With the help of boost::iterator_facade and stackoverflow.com [1], I've 
almost managed to adapt the Ring concept to my legacy objects, but I got 
a compile time error which I don't understand. As you can see from the 
code, the iterator exposes QPoint* objects directly, so that should work 
properly.

The cpp files and the errors from the build log is here [2].

[1] 
http://stackoverflow.com/questions/9251537/how-to-create-a-boost-range-that-hides-multiple-layers-of-vectors-and-exposes-it
[2] https://gist.github.com/1852693

Regards,
Mats Taraldsvik

On 02/12/2012 05:11 PM, Barend Gehrels wrote:
> 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 
>>>> <http://www.boost.org/doc/libs/1_48_0/libs/geometry/doc/html/geometry/reference/concepts/concept_point.html>", 
>>>> 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 
> ring-pieces.
>
> Regards, Barend
>
>
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