[geos-devel] Is Overlay-NG active?

[Roger Bivand]

On Thu, 15 Oct 2020, Regina Obe wrote:

> Roger,
>
> I'll let Paul answer the question of when we can expect a 3.9 as he 
> probably has a better idea than anyone else. All I know is the plan is 
> we'll be releasing GEOS 3.9 and PostGIS 3.1 around the same time since 
> there is some functionality in PostGIS 3.1 that leverages GEOS 3.9 if it 
> is compiled with GEOS 3.9.
>
> As far as testing, on the PostGIS side to make the old Geos and new Geos 
> agree, I've been applying ST_Normalize
>
> Which looks to come from Geos CAPI - GEOSNormalize
>
> Can you use that to deal with the failures you are running into?  That 
> should make the wkt of both GEOS old and new agree.

Thank you, yes, probably. However, both legacy overlay and Overlay-NG 
differ from GEOSNormalize() (as far as I can see from a simple test), so 
the half-dozen package maintainers will need to go from legacy to 
normalized and then avoid having to condition on the GEOS version.

Best wishes,

Roger

>
> Thanks,
> Regina
>
>> -----Original Message-----
>> From: geos-devel [mailto:geos-devel-bounces at lists.osgeo.org] On Behalf Of
>> Paul Ramsey
>> Sent: Thursday, October 15, 2020 12:39 PM
>> To: Roger.Bivand at nhh.no; GEOS Development List <geos-
>> devel at lists.osgeo.org>
>> Subject: Re: [geos-devel] Is Overlay-NG active?
>>
>> The "plan" as I see it is to, for 3.9, actually make NG the default for the
>> standard intersection(), union(), unaryunion(), difference(), symdifference()
>> calls. So the "test" will be "is this GEOS 3.9". I don't want to go forward into
>> the future where a released GEOS has two potential behaviour modes, that
>> way lies madness. We needed to keep a switch in place to allow other
>> development to continue and to compare before/after easily on the working
>> branch (and to allow people like you to test the new without suddenly have
>> everything break on ordinary testing).
>>
>> Does that make sense?
>>
>> P
>>
>>> On Oct 15, 2020, at 8:59 AM, Roger Bivand <Roger.Bivand at nhh.no> wrote:
>>>
>>> Can I ask whether there is, or could be, a function exposed in the C_API, or
>> a header variable say in geoc_c.h, showing whether the running GEOS is
>> using Overlay-NG or not?
>>>
>>> After help from the list, I've now run checks on R packages either
>> themselves linking to GEOS, or using functions from packages which do link
>> to GEOS. A half-dozen or so fail on unit tests, typically because the ordering
>> of coordinates varies (say same polygon, but starting at  a different place), or
>> the ordering of sub-geometries (say slivers from a Union operation) varies
>> from before Overlay-NG. The objects are the same (for given precision), but
>> unit tests in packages compare the WKT of the output geometry with the
>> expected WKT (often generated from output before Overlay-NG).
>>>
>>> So if we could provide a way for the unit tests to compare correctly
>> branching on Overlay-NG or not, the package maintainers could avoid having
>> to scramble when platforms and R packages linking to GEOS begin to appear.
>>>
>>> Another question raised by package maintainers - do we know when 3.9.0
>> may be expected, and will it have Overlay-NG? However, providing them
>> with an easy way to ask the GEOS runtime if it is Overlay-NG or not will
>> relieve the pressure.
>>>
>>> Anyway, the failure count is very low, a half-dozen from hundreds is fine
>> (and if they didn't write tests, that isn't our problem...).
>>>
>>> Roger
>>>
>>> --
>>> Roger Bivand
>>> Department of Economics, Norwegian School of Economics, Helleveien 30,
>>> N-5045 Bergen, Norway.
>>> voice: +47 55 95 93 55; e-mail: Roger.Bivand at nhh.no
>>> https://orcid.org/0000-0003-2392-6140
>>> https://scholar.google.no/citations?user=AWeghB0AAAAJ&hl=en
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>>> geos-devel at lists.osgeo.org
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>>
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>
>

-- 
Roger Bivand
Department of Economics, Norwegian School of Economics,
Helleveien 30, N-5045 Bergen, Norway.
voice: +47 55 95 93 55; e-mail: Roger.Bivand at nhh.no
https://orcid.org/0000-0003-2392-6140
https://scholar.google.no/citations?user=AWeghB0AAAAJ&hl=en