Re: [Boost-users] [Geometry] please help; using buffer() extensions

Subject: Re: [Boost-users] [Geometry] please help; using buffer() extensions
From: Barend Gehrels (barend_at_[hidden])
Date: 2013-02-27 09:12:12

Hi John,

On 25-2-2013 20:38, John Lilley wrote:
>
> (sorry another post; someone told me to put [library name] in [] in 
> subject... learning something new every day J
>
> Something of a repost, but I've learned a bit more on the path to 
> being truly confused.  It appears that 
> boost\geometry\extensions\algorithms\buffer\buffer_inserter.hpp 
> contains some specializations for buffering other shape types?  But 
> I'm out of my depth here... is there an example?
>

Not in the examples folder or the docs, but the test contains lots of 
examples. Well, they all do the same thing, so what is done is this:

     join_miter
         <
             point_type,
             typename bg::point_type<GeometryOut>::type
         > join_strategy;

     typedef bg::strategy::buffer::distance_assymetric<double> 
distance_strategy_type;
     distance_strategy_type distance_strategy(distance_left, 
distance_right);
     std::vector<GeometryOut> buffered;
     bg::buffer_inserter<GeometryOut>(geometry, 
std::back_inserter(buffered),
                         distance_strategy,
                         join_strategy);

> What do I need to do in order to buffer:
>
> a point?
>

Not possible yet.

> A linestring?
>

See above.

> A vector of polygons?
>

If you mean a multipolygon: see above.

> A heterogeneous collections of shapes?
>

Not possible yet.

> Is this generalization of buffer also going to work as a "deflate" for 
> polygons?
>

Yes, the distance may be positive and negative. A negative distance will 
result in a deflate.

> If someone can tell me "include these headers, use these algorithms", 
> it will help a lot!
>

I'll try to come with a more up to date example, now that the buffer is 
a hot topic again.

Regards, Barend