Add curve support to ST_AsSVG

[mdavis]

It should be straightforward to enhance ST_AsSVG to support curved geometries (i.e. CircularString, CompoundCurve, CurvePolygon, MultiCurve, MultiSurface). This will provide a PosstGIS-native way to visualize curved geometry, which is not widely supported by other tools.

This can be done easily using ​SVG elliptical arcs.

[pramsey]

Milestone renamed

[robe]

In prep for 3.1.3 release

[robe]

Speaking of which I have this as a TODO for X3D as well #1416. I think it would be implemented in X3d using nurbs ​https://www.web3d.org/x3d/content/examples/Basic/NURBS/, In particular for 2D the geometries would be expressed as Contour2D and Contour2DPolyine ​https://www.web3d.org/documents/specifications/19775-1/V3.3/Part01/components/nurbs.html#X3DParametricGeometryNode It's too bad we don't support 3D curves since Nurbs in X3d could handle those.

[robe]

Was looking at this while I was looking at my X3D adding curves. I think adding curves to SVG should be much easier than my X3d, so I'll take a stab at this.

I'll push to 3.5.0 for now, and if I get to it before then will push back to 3.4.0

[robe]

Work in progress here - ​https://git.osgeo.org/gitea/robe/postgis/src/branch/svg-curve-support

at moment only supports CIRCULARSTRING

[robe]

Now also supports COMPOUNDCURVE and MULTICURVE.

[Regina Obe <lr@…>]

In 39c69beb/git:

ST_AsSVG support for curves

• Support circularstring, compoundcurve, multicurve, curvepolygon, multisurface in svg (absolute)
• Relative work in progress
• Update cu_out_svg.c moving curve examples from unsupported to test mode
• Update docs to reflect curves now supported

Closes #4913
Closes ​https://git.osgeo.org/gitea/postgis/postgis/pulls/130