Geometry Boost List: Re: [geometry] point on/intersects linestring?

Subject: Re: [geometry] point on/intersects linestring?
From: Adam Wulkiewicz (adam.wulkiewicz_at_[hidden])
Date: 2013-09-03 15:53:56

Barend Gehrels wrote:
> Hi Adam,
>
>
> On 3-9-2013 15:02, Adam Wulkiewicz wrote:
>> Adam Wulkiewicz wrote:
>>> AFAIK there isn't and intersects() for Box-Linestring isn't yet 
>>> implemented. There is a function calculating the comparable distance 
>>> of a Linestring/Segment-Box intersection but it's in the 
>>> index::detail so currently isn't a part of the official interface. 
>>> Barend should I add some parts of it to the bg::intersects()?
>>
>> For example something like in the patch.
>
> Yeah, I looked at the referred website and the patch
>
> Thanks a lot for your efforts and quick work, this looks promising.
>
> But do we need to develop it from scratch again?
>
> It has a considerable overlap with the current implementation of 
> clipping a linestring (or segment) with a box. See also 
> algorithms\detail\overlay\clip_linestring.hpp This file is not touched 
> (or looked at by me) for a long long time, I just looked at it again 
> and it is a bit old style. I did not test it but it seems that it 
> (especially the liang_barsky strategy) returns exactly if a segment is 
> clipped by a box, in a comparable way.
>

Ok, I didn't know about it.

> Did you write a unit-test for this when you developed this?

I have written only a test for the implementation in the Index. Not yet 
for this one

> I'm curious:
> - if it works for 3d (the strategy above does not)

It should work for n-dimensional cartesian boxes, segments and linestrings.

> - does it return false when the whole segment is inside? Don't see 
> that in the article.

intersects() returns true.

> - does it work for degenerate segments (point 1 == point 2)? Seeing 
> the patch it will divide by zero then?

Hmm, I probably haven't thought about this particular case, only the 
case when the segment is parallel to the edge (the difference of 
coordinates for this dimension is also 0), but I've just tested it and 
it works.

Regards,
Adam