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

Paul Ramsey pramsey at cleverelephant.ca
Wed Jul 3 07:35:29 PDT 2019

Also, what are the results of ST_Distance() when the distance is < tolerance? Zero? Tolerance?
Basically tolerance is a cross-cutting concern that affects almost every function in the system, sometimes in ways that ordinary users might consider “surprising” or “counter intuitive”. Our current “as much precision as we can take” system still has wonderful corner cases since we don’t actually have infinite precision at our command: the results of ST_Intersection(A, B) does not necessarily ST_Intersects() A or B.
The new overlay work in GEOS requires explicit precision, so we are going to start inching in that direction over time. Until then, enforcing precision on insert/update with triggers is not the end of the world if you want command of your precision model.

> On Jul 3, 2019, at 5:47 AM, Darafei Komяpa Praliaskouski <me at komzpa.net> wrote:
> 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 <mailto: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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