Changes between Version 3 and Version 4 of ToleranceDiscussion

Timestamp:

Mar 28, 2012, 3:17:04 PM (12 years ago)

Author:

Mike Taves

Comment:

add GEOS PrecisionModel idea

ToleranceDiscussion

@@ -32 +32 @@
 A regular grid (like shown in the paper) would only take a size (vertical and horizontal) to share.
 An irregular grid (FP expanding grid?) would take an equivalent calculus to compute.
+
+=== GEOS !PrecisionModel ===
+The [http://geos.refractions.net/ro/doxygen_docs/html/classgeos_1_1geom_1_1PrecisionModel.html geos::geom::PrecisionModel GEOS PrecisionModel Class] was ported from JTS to the GEOS C++ API, but there is no C API for this feature. Adding a !PrecisionModel to the GEOS functionality uses a precision grid to "snap" all coordinates, which could eliminate some rounding and robustness issues with some functions.
+
+The functionality can be previewed graphically with JTS !TestBuilder, in the top menu Edit > Precision Model ... For example, if you want to have millimetre tolerance, set the fixed to "1000.0", now an input geometry of `'POINT (130.111 281.999)'` will remain the same, but an input of `'POINT (130.1111 281.9999)'` will auto magically snap to `'POINT (130.111 282)'`. Other functions, such as buffer, will also have results that conform to no more than millimetre precision (three decimal places).
+
+In order for this functionality to be used in PostGIS, it would first need to be exposed to the GEOS C API. Secondly, PostGIS would need to somehow communicate the precision model to be used, based on some metadata. As a first pass idea, the topology extension has a few metadata tables, where a tolerance could somehow be specified. I'm not sure how it could be implemented to other geometries without a server runtime variable (e.g., [http://www.postgresql.org/docs/current/static/runtime-config-custom.html Customized Options]).