[postgis-users] PostGIS new geometry type with defined precision?

Martin Davis mtnclimb at gmail.com
Wed Jul 3 07:54:18 PDT 2019

JTS already provided a mechanism to specify a precision for geometry, and
this is respected by a number of operations as well (notably the overlay
operations intersection et al and buffer - but not the spatial predicates,
yet).  GEOS should provide this as well, or is close to doing so.  And I'm
currently working on a new implementation of overlay to improve robustness,
which will improve fixed precision computation as well.

The issue of handling fixed precision for predicates is a good question.  I
have an algorithm in the conceptual stages for this.  But it may be
difficult to make it consistent with the overlay operations on a performant
way.  I intend to write up a survey of the options soon.

My current thinking is that precision will be specified as a parameter to
geometry operations.  No new type will be required. It might be nice to
have precision specified in column metadata somehow, but not sure how this
could work

On Wed, Jul 3, 2019, 5:48 AM Darafei "Komяpa" Praliaskouski <me at komzpa.net>

> Hi,
> Can you describe how the operations like Intersection should behave in
> such type? E.g. if you have a type with 0 decimals (say), and have a line
> going from (0,0) to (1,1) intersect with a line going from (1, 0) to (0, 1)
> - what is the intersection point that is going to be reported? Will that
> ST_Intersection in turn ST_Intersects=true with original point?
> There are a number of such requests across the years but nobody seems to
> propose a working algebra for such type, and without it it's not going to
> get implemented.
> On Wed, Jul 3, 2019 at 2:43 PM Giunta Igor <Igor.Giunta at tg.ch> wrote:
>> How can a precision be assigned to a geometry, e.g. a point/line/polygon
>> to 3 decimals, in order that any input/output will be given in that
>> precision (without usage of rounding functions like snap2grid)
>> How can the problem be tackeld? Shall we request to include new types? Or
>> shall we rather let develop a new feature?
>> I guess we are not the first users facing this problem.
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> --
> Darafei Praliaskouski
> Support me: http://patreon.com/komzpa
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