[postgis-devel] ST_Buffer - single sided option

[Darafei "Komяpa" Praliaskouski]

Hi,

Thoughts that I have:

 - this is a cool thing that I've needed multiple times. I worked around
its absence by fiddling with ST_MakeLine(ST_Collect(line,
ST_OffsetCurve(line, 1))) and then trying to make result valid, which
sometimes worked;
 - how do I remember which way is it being offset? I expect
ST_Buffer(ST_Boundary(ST_ForceRHR(polygon)), 10, 'single_side') to be
buffered "outside". Does it hold true?
 - if there are no better ideas on ST_Buffer signature I'd say your option
is good enough for me;
 - there's no error reporting mentioning `single_side` as valid option;
 - can `single_side=1` also work for `single_sided=1` and just
`single_side`/`single_sided`?
 - what does it do for line and for point?
 - does it work on EMPTY, LINESTRING(0 0, 0 0), MULTILINESTRING, and
self-intersecting one?
 - how do I reverse the direction of buffering? I understand there's
negative buffer parameter, does it work? I see you parse parameter to be
single_side=1/0, maybe -1 will also make sense?
 - out of curiosity, will ST_Buffer(geom,0,'single_side') fix invalid
geometries? :)

As someone responsible for github in PostGIS, I encourage you to put it to
GitHub as a PR: that'll get you test coverage report, travis CI greenlight,
a way to comment on your patch inline, and usual PR merge time on it
recently improved. :)

чт, 18 янв. 2018 г. в 12:56, Stephen Knox <stephenknox73 at gmail.com>:

> Hi List,
>
> I noticed that PostGIS didn't implement the single-sided buffer
> functionality of Geos (NB. not the Offset Curve functionality, but a
> polygon), so have submitted a patch to implement that:
> https://trac.osgeo.org/postgis/ticket/3989
>
> I have refrained from adding tests and documentation until I get some
> agreement that the function signature is acceptable, as I am a new
> contributor, and I think the ST_Buffer signature is already quit "unusual"
> in that it implements text parameters.
>
> I was hoping that post the recent patch releases, a more experienced
> contributor might be able to look at my (small) patch and give some
> feedback.
>
> I can put it up on Github as well if that would help.
>
> Many thanks
>
> Stephen
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