Geometry Boost List: [ggl] Questions about Boost.Geometry

Subject: [ggl] Questions about Boost.Geometry
From: Dragos Chirila (dchirila)
Date: 2011-05-18 23:24:17

Thank you very much for the feedback.

I guess the best approach for me is to finish my geometry mini-library, and
later try to replace it with Boost.Geometry as the issues you mentioned are
fixed.

In any case, I am looking forward to seeing Boost 1.47, and Boost.Geometry
in particular.

Best wishes,
Dragos

On 17 May 2011 23:10, Barend Gehrels <barend_at_[hidden]> wrote:

> Hi Dragos,
>
> Welcome to the list!
>
>
>
>  I am developing a small C++ framework (which I plan to release as
>> open-source soon), focusing on post-processing of climate datasets. Some
>> computational geometry is a necessary component (for example, for filtering
>> data inside a polygon on the sphere). For this component, I am currently
>> trying to implement a separate library.
>>
>
>
> Very interesting.
>
>
>
>  1. (Approximately) when will the "official" Boost-version be released? I
>> am already using other Boost libraries, and my core users would prefer to
>> use a single, stable Boost package.
>>
>
>
> I see. It is already late, but I'm not sure about the exact date. Right at
> this moment there is BoostCon 2011 , people were busy with that, and I think
> more news about the date will come next week.
>
> It will be about June/July, I guess.
>
>
>
>
>> 2. For an initial version of my software, simple spherical coordinates
>> would suffice. Therefore, can Boost.Geometry (using the spherical coordinate
>> system):
>>
>> a) determine whether a GeoLocation (lon, lat) lies inside a GeoPolygon
>> (specified as a vector of (lon,lat)-pairs)?
>>
>
>
> At this moment: no. This is because there was a bug in the side-routine for
> lon,lat. But the using point-in-polygon algorithm is agnostic so depends on
> that side, if it is fixed, yes. I postponed this last months for other
> priorities, but probably it is very small, will have a look, at least to the
> state of it.
>
>
>
>
>> * This is not a problem for my geometric routines, since I can use a
>> cylinder projection, then compute as in the plane case. But can this be
>> easily achieved with Boost.Geometry?
>>
>> b) compute the area of intersection between two GeoPolygons?
>>
>
>
> No, it is planned but not implemented. This depends also on side but, more
> important, to segment-intersection which should be correctly implemented for
> lon,lat segments. Also the bounding box (used e.g. for partitioning) should
> be considered / handled in the right way, for spherical. If  all that is
> done, it should basically run but there will some things to finetune.
>
> Yes, it would be exciting if this is running correctly.
>
>
>
>
>> * This is actually one of my biggest problems, since my (non-specialist)
>> solution is to:
>> - project both GeoPolygons onto a plane cutting the sphere;
>> - compute the clipping polygon in 2D, then
>> - project back on the sphere and
>> - compute the area of the spherical polygon.
>>
>
>
> I see, this is not the ideal solution.
>
>
>
>
>> This does not feel like a good solution, and has many limitations
>> (depending on the size of the GeoPolygons, a projection plane might not
>> exist, in which case I have to divide them and try to repeat the procedure).
>> So, is this possible (maybe trivial) in Boost.Geometry?
>>
>
>
> I'm quite sure it is feasible but it will certainly not be in Boost 1.47
>
>
>
>
>> I hope this is the right place for these questions. Any input would be
>> greatly appreciated!
>>
>
>
> Sure this is the right place.
>
> Regards, Barend
>
> _______________________________________________
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>

-- 
================================================
= Dragos B. Chirila
= Computational Physicist, PhD candidate
= Alfred Wegener Institut Bremerhaven, University of Bremen
= [phone]
================================================
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