Geometry Boost List: Re: [geometry] Incorrect results from bg::equals (problem with closure and collect_vectors?)

Subject: Re: [geometry] Incorrect results from bg::equals (problem with closure and collect_vectors?)
From: Ch'Gans (chgans_at_[hidden])
Date: 2017-04-09 02:06:28

On 9 April 2017 at 12:05, Adam Wulkiewicz <adam.wulkiewicz_at_[hidden]> wrote:
> Hi,
>
> Ch'gans Via Geometry wrote:
>>
>> Hi there,
>>
>> My custom ring type is defined with an 'open' closure.
>>
>> When i try to compare 2 geometrically equivalent ring and box,
>> bg::equals return false.
>> While investigating using the debugger, i discovered that the call to
>> geometry::collect_vectors() returns 4 points for a box, but only 3
>> points for a ring, so my 2 geometries can never be equal.
>>
>> In my case, collect_vectors is dispatched to range_collect_vectors,
>> and by the look of it range_collect_vectors doesn't care about the
>> geometry object (and it's closure), since it sees only point
>> (iterator) range.

[...]
>> Am i missing something in my custom geometry trait adaptation? is it a
>> bug in BG, or a known limitation?
>
> It is a bug. I pushed a fix to develop:
> https://github.com/boostorg/geometry/commit/657a5c80902edc9640a06571c2762a5dee591067
> I'll try to release it with Boost 1.64.

Hi Adam,

Thanks for the fix, this was quick! ;)
After adding the QVM dependency, and using Geometry devel branch, I
have removed a couple of expected failure from my test suite, great!

But unfortunately i still have some left: Comparison for geometry
equivalence of a box and a ring.

The problem is again in collect_vectors, the specialisation for bbox
always collect the points by following the clockwise direction, if
your have counterclockwise rings then equals(ring, box) will always
return false due to different directions.

Not sure what is the best way to fix this, any thoughts?

Chris