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C3D-CURBOFF · Offset curb 0.5 and 2.0 toward road done

Offsets each curb Polyline on SS-V-ROAD-CURB by 0.5ft (top face) and 2.0ft (flowline) toward the road. Direction chosen per run by testing both sides and keeping the one farther from the building centroid.

C# payload

// STEP 2: curb-and-gutter offsets. TBC (top back of curb) is the surveyed line; offset it
// TOWARD THE ROAD by 0.5' (top face of curb) and 2.0' (flowline / gutter lip).
// Direction per run: offset both ways, keep the side whose midpoint lands FARTHER from the
// building footprint centroid (the road side). Runs are drawn in arbitrary directions so a
// fixed left/right rule does not work.
// Host owns Tx/ModelSpace - no using/Commit here.
const string LAYER = "SS-V-ROAD-CURB";
const double MINLEN = 3.0, MAXLEN = 500.0;

// building centroid = the "away from road" reference
double bx = 0, by = 0; int bn = 0;
foreach (ObjectId id in ModelSpace)
{
    var e = Tx.GetObject(id, OpenMode.ForRead) as Autodesk.AutoCAD.DatabaseServices.Entity;
    if (e == null || e.Layer != "SS-V-BLDG-OTLN") continue;
    var p = e as Polyline;
    if (p == null) continue;
    for (int i = 0; i < p.NumberOfVertices; i++) { var v = p.GetPoint2dAt(i); bx += v.X; by += v.Y; bn++; }
}
if (bn == 0) { Log("No building outline found - cannot determine road side."); return; }
bx /= bn; by /= bn;
Log($"Building centroid ({bx:F2},{by:F2}) from {bn} verts.");

var srcs = new List<ObjectId>();
foreach (ObjectId id in ModelSpace)
{
    var e = Tx.GetObject(id, OpenMode.ForRead) as Autodesk.AutoCAD.DatabaseServices.Entity;
    if (e == null || e.Layer != LAYER) continue;
    var p = e as Polyline;
    if (p == null) continue;
    if (p.Length < MINLEN || p.Length > MAXLEN) continue;
    srcs.Add(id);
}
Log($"{srcs.Count} curb Polylines to offset.");

double DistFromBldg(Autodesk.AutoCAD.DatabaseServices.Entity e)
{
    var p = e as Polyline;
    if (p == null || p.NumberOfVertices == 0) return -1;
    double mx = 0, my = 0;
    for (int i = 0; i < p.NumberOfVertices; i++) { var v = p.GetPoint2dAt(i); mx += v.X; my += v.Y; }
    mx /= p.NumberOfVertices; my /= p.NumberOfVertices;
    return System.Math.Sqrt((mx-bx)*(mx-bx) + (my-by)*(my-by));
}

int made = 0, failed = 0;
foreach (var id in srcs)
{
    var pl = (Polyline)Tx.GetObject(id, OpenMode.ForRead);
    int sign = 0;
    try
    {
        var pos = pl.GetOffsetCurves(0.5);
        var neg = pl.GetOffsetCurves(-0.5);
        double dp = pos.Count > 0 ? DistFromBldg((Autodesk.AutoCAD.DatabaseServices.Entity)pos[0]) : -1;
        double dn = neg.Count > 0 ? DistFromBldg((Autodesk.AutoCAD.DatabaseServices.Entity)neg[0]) : -1;
        if (dp < 0 && dn < 0) { failed++; continue; }
        sign = (dp >= dn) ? 1 : -1;
    }
    catch { failed++; continue; }

    foreach (double d in new double[] { 0.5, 2.0 })
    {
        try
        {
            var curves = pl.GetOffsetCurves(sign * d);
            foreach (Autodesk.AutoCAD.DatabaseServices.Entity oe in curves)
            {
                oe.Layer = LAYER;
                ModelSpace.AppendEntity(oe);
                Tx.AddNewlyCreatedDBObject(oe, true);
                made++;
            }
        }
        catch { failed++; }
    }
}
Log($"Created {made} offset curves (0.5' face + 2.0' flowline) from {srcs.Count} runs. {failed} failures.");

Result

Building centroid (2428047.81,1064467.84) from 17 verts.
62 curb Polylines to offset.
Created 125 offset curves (0.5' face + 2.0' flowline) from 62 runs. 0 failures.