3D intersection on GML solids: “SFCGAL support not enabled” in .NET 8 (PolyhedralSurface Z)

[Mganjirad]

Hi, and thanks for providing this great library.

I’m building a .NET 8 service and I’ve run into a problem with 3D geometric operations on GML solids. I’d like to describe the scenario in detail and ask for guidance on the recommended approach and configuration.

Scenario

• Platform: .NET 8, C#
• Library: max.rev.gdal.universal
• Input: two GML files, each containing a 3D solid geometry
• Workflow:
  1. Read both GML files using max.rev.gdal.universal
  2. Convert the geometries to WKT
  3. The resulting WKT geometries are of type:
     PolyhedralSurface Z
  4. Perform 3D geometric operations between these two solids

Goal

I need to perform actual 3D operations on these solid geometries, such as:

• Computing the intersection of the two solids and returning the resulting 3D geometry
• Checking whether the two solids share a common boundary
• Detecting whether the faces (planes) of the two solids touch each other (contact without overlapping volume)
• Potentially other 3D boolean / topological operations in the future

Problem

When I attempt to perform intersection (and similar operations) on these 3D geometries, I get the following exception:

SFCGAL support not enabled.

As far as I understand, GEOS alone is mostly 2D, and 3D operations (especially on PolyhedralSurface Z / solid geometries) generally require SFCGAL. It looks like the underlying GDAL/GEOS stack used by max.rev.gdal.universal does not have SFCGAL enabled, or at least it’s not available from .NET in my current setup.

Questions

I would really appreciate clarification on the following points:

1. SFCGAL support in max.rev.gdal.universal

   • Does the GDAL build shipped/used by max.rev.gdal.universal have SFCGAL enabled for 3D operations?
   • If not, is there a supported way to:
     • Use a GDAL build with SFCGAL support from .NET via this package?
     • Or configure the library to work with a custom GDAL/SFCGAL build?

2. Recommended approach for 3D boolean operations

   For 3D solids coming from GML (converted to PolyhedralSurface Z), what is the recommended approach within the context of this library to perform:

   • 3D intersections
   • Common boundary detection
   • Detection of touching faces / surfaces

   Is it expected that these 3D operations are handled via GDAL+SFCGAL underneath, or is there a different intended path?

3. Limitations / scope of the current .NET bindings

   • Are there known limitations in the current .NET bindings (or in the GDAL/GEOS stack bundled with this package) regarding:
     • 3D geometry types
     • PolyhedralSurface Z
     • Solid boolean operations
   • If 3D intersects/overlaps are out-of-scope for this package, it would be helpful to know that explicitly.

4. Suggested alternatives or architecture

   If full 3D support via SFCGAL is not available or recommended through max.rev.gdal.universal, do you have any suggestions for:

   • Alternative libraries or approaches (e.g., using an external 3D engine, other .NET bindings, etc.)
   • A typical architecture where:
     • GML is parsed via GDAL
     • 3D operations are delegated to another specialized library / service
     • And results are then brought back into the .NET pipeline

Summary

In short:
I can successfully read GML and convert to PolyhedralSurface Z WKT using max.rev.gdal.universal in .NET 8, but I cannot execute 3D intersection and related operations due to the "SFCGAL support not enabled." exception. I’m trying to understand:

• Whether 3D/SFCGAL-based operations are expected to work with this package
• What configuration or build is required
• Or whether I should rely on a different approach for 3D solid operations in .NET

Any guidance, clarification, or documentation pointers would be greatly appreciated.
Thank you for your work on this project and for any help you can provide.

[MaxRev-Dev]

Hi, thanks for the detailed report.
The current runtime packages do not ship GDAL with SFCGAL enabled. They include GEOS/PROJ, but not SFCGAL.

This package can read/export those geometries through GDAL, but it does not extend GDAL behavior. GEOS/NTS are useful for 2D/planar operations, validation, filtering, and preprocessing, but they are not suitable for true 3D solid boolean/topological operations.
here is no runtime flag to enable SFCGAL in the published NuGet packages. To use SFCGAL via GDAL/OGR, you would need a custom native GDAL build with GDAL_USE_SFCGAL=ON and ship SFCGAL plus its dependencies with the runtime.

Recommended architecture: use this package for GML/GDAL I/O, then delegate 3D intersection / common-boundary / touching-face logic to a dedicated 3D engine, such as PostGIS with postgis_sfcgal, native SFCGAL/CGAL, or a private SFCGAL-enabled GDAL build.

SFCGAL support can be added in a future release, but I can’t commit to a release date yet.