Review request: ST_Clothoid WKT/WKB support (libgeos/geos#1566)

[Jeroen Bloemscheer]

Hi all,

I've opened a pull request adding a clothoid (Euler spiral) curve type to GEOS and would appreciate reviews:

GEOS PR #1566<https://github.com/libgeos/geos/pull/1566>

What it adds

  *   A Clothoid geometry following ISO/IEC 13249-3:2016 ST_Clothoid, represented by an affine placement, scale factor, and start/end distances from the inflection point.
  *   WKT read/write using the SQL/MM CLOTHOID syntax, including Z, M, ZM, and EMPTY.
  *   WKB read/write as type 22, with 1022/2022/3022 for Z/M/ZM.
  *   Length, envelope, and linearisation, including clothoid sections within a CompoundCurve.
  *   GEOSGeom_createEmptyClothoid in the C API.

Distance, intersection, and point-location operations currently throw on clothoids rather than silently falling back to a chord, so unsupported operations fail explicitly instead of returning an incorrect result.

Numerics

Points and headings are computed using Fresnel integrals. Beyond |t/A| = 9, the implementation switches to asymptotic auxiliary functions. Headings are reduced using a 159-bit representation of 2π, keeping accuracy at around 1e-16 of the curve extent even far from the inflection point.

Tests compare against a high-precision reference and cover numerical edge cases and error paths.

Where I'd especially appreciate feedback

  1.  The new GEOS_CLOTHOID type ID (13), particularly its ABI implications and the effect on code switching on GeometryTypeId.
  2.  The new virtual SimpleCurve::addLinearizedPoints, which allows CompoundCurve to linearise its sections without explicit type checks.
  3.  Whether throwing for unsupported operations is the right default, or whether some operations should linearise first.
  4.  The C API addition and WKB encoding. ISO WKB cannot mark an empty clothoid nested inside a collection, so the reader has a specific rule for that case.

The PR is deliberately limited to I/O and basic curve support. ST_SpiralCurve, predicates, overlay, buffer, and GML are left for follow-up work.

Thanks for taking a look.

Jeroen Bloemscheer

________________________________
Jeroen Bloemscheer
Geo-IT Consultant
Zaltbommel
[Merkator]

m: +31 (0)6 478 728 18
e:  jeroen.bloemscheer at merkator.com


Merkator BV
Hogeweg 137a
5301 LL Zaltbommel(NL)
www.merkator.com<https://www.merkator.com/>     [LinkedIn] <https://www.linkedin.com/company/2400587>
________________________________

This email (including any attachments to it) is confidential, legally privileged, subject to copyright and is sent for the personal attention of the intended recipient only. If you have received this email in error, please advise us immediately and delete it. You are notified that disclosing, copying, distributing or taking any action in reliance on the contents of this information is strictly prohibited. Although we have taken reasonable precautions to ensure no viruses are present in this email, we cannot accept responsibility for any loss or damage arising from the viruses in this email or attachments. We exclude any liability for the content of this email, or for the consequences of any actions taken on the basis of the information provided in this email or its attachments, unless that information is subsequently confirmed in writing.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/geos-devel/attachments/20261024/63999d71/attachment-0001.htm>