LINQ spatial queries

EngrCAD.Query makes geometry LINQ-queryable with an index: a SpatialCollection<T> pairs items with a bounds expression and builds a BVH; its custom IQueryable provider recognizes spatial predicates inside Where clauses and answers them from the BVH instead of scanning.

var mesh = Shape.Sphere(10).ToMesh();

// Index the mesh faces by their bounding boxes.
var faces = mesh.Faces.ToSpatialCollection(f => f.Bounds);

// The .Within clause is routed to the BVH; the rest of the predicate still applies.
var region = new Aabb((0, 0, 5), (10, 10, 10));
var hits = faces.AsQueryable()
    .Where(f => f.Bounds.Within(region))
    .ToList();

Console.WriteLine($"{hits.Count} of {faces.Count} faces intersect the region");
if (!faces.LastQueryUsedIndex)
    throw new Exception("expected the BVH to answer the spatial clause");
if (hits.Count == 0 || hits.Count == faces.Count)
    throw new Exception("candidate set should be a proper subset");

// Distance and ray predicates use the same index. Build the arguments *outside*
// the predicate — expression trees cannot contain tuple conversions, so the
// tuple-to-vector shorthand is unavailable inside a Where lambda.
var northPole = new Vector3d(0, 0, 10);
var downRay = new Ray3d((0, 0, 30), (0, 0, -1));
var nearOrigin = faces.AsQueryable()
    .Where(f => f.Bounds.WithinDistance(northPole, 2.0))
    .ToList();
var underRay = faces.AsQueryable()
    .Where(f => f.Bounds.HitBy(downRay))
    .ToList();
Console.WriteLine($"{nearOrigin.Count} near the north pole, {underRay.Count} under the ray");
if (nearOrigin.Count == 0 || underRay.Count == 0)
    throw new Exception("expected nonempty results");

How it works

• The predicate vocabulary is SpatialPredicates: .Within(box), .WithinDistance(point, distance), .HitBy(ray) applied to the registered bounds accessor. These exist because expression trees cannot contain calls to methods with in parameters, which the kernel API uses — the wrappers take parameters by value.
• Interception is a pure optimization: the full original predicate is re-applied over the BVH candidates, so results can never differ from LINQ-to-Objects; anything the provider doesn’t recognize falls back to LINQ-to-Objects entirely. LastQueryUsedIndex is the diagnostic for whether the index was used.
• B-Rep topology has its own LINQ vocabulary (BrepQueries: IsPlanar, IsCylindrical, IsCircular, Length, face.Edges(), solid.FacesOf(edge)), which powers the chamfer & fillet selectors; mesh handles support topology traversal (vertex.OutgoingHalfEdges(), face.AdjacentFaces()).

No screenshot on this page — the interesting output is the query plan, not pixels.