feat: terrain mesh from the DEM, and correct the blockout frame
Tools/terrain_from_dem.py builds a 191x106 grid at 2 m over the block, Z being NAVD88 minus the origin ground. Building footprints from the OSM extract are cut out so rooftops never become terrain (72 footprints, 6310 cells). Spot checks reproduce the measured profile: origin 0.00, Orange Dr +3.39, south gutter +0.93, crown +1.38, north sidewalk +1.43. Blosm projects with a sphere, not an ellipsoid, so its frame was ~0.4% oversized and rotated by meridian convergence: about 2 m at the theatre. The blockout now fits a six-parameter affine into EPSG:26911 on five control points (0.0 cm residual) and transforms root objects only, since children inherit and double transforming them read as a 2 m placement error.
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"""Build a terrain mesh from the committed 3DEP DEM, in project-local metres.
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Run inside Blender (background or GUI):
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B=/var/lib/flatpak/app/org.blender.Blender/x86_64/stable/active/files
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LD_LIBRARY_PATH="$B/blender/lib" "$B/blender/blender" -b --factory-startup \
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--python Tools/terrain_from_dem.py -- \
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--dem Geo/raw/dem-3dep-1m-26911-2026-11-06.tif \
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--out Art/blender/terrain/terrain-2026-11-06.blend
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Coordinates follow `Geo/manifests/local-origin.md`:
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* X = UTM easting − 376 515.389 (east positive)
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* Y = UTM northing − 3 774 224.083 (north positive)
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* Z = NAVD88 elevation − 115.911 (the DEM value at the origin)
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The DEM is already EPSG:26911, so no reprojection happens here: pixel centres are
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UTM, and only the origin subtraction is applied. Negative X is west, negative Y
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is south — the whole block sits at negative X.
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The mesh is a regular grid at `--step` metres (default 2, which still resolves
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the ~2 % road crown over the ~21 m carriageway). Nodata cells are skipped by
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dropping faces that touch them, so no fake geometry is invented at the edges.
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"""
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import argparse
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import os
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import sys
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import subprocess
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import bpy
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sys.path.insert(0, os.path.join(os.path.dirname(os.path.abspath(__file__)), "..", "Geo", "scripts"))
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import dem_stats # noqa: E402
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import osm_common as oc # noqa: E402
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ORIGIN_E = 376515.389
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ORIGIN_N = 3774224.083
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ORIGIN_Z = 115.911
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def parse_args():
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argv = sys.argv
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argv = argv[argv.index("--") + 1:] if "--" in argv else []
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ap = argparse.ArgumentParser()
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ap.add_argument("--dem", required=True)
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ap.add_argument("--out", required=True)
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ap.add_argument("--step", type=float, default=2.0, help="grid spacing in metres")
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ap.add_argument("--xmin", type=float, default=-330.0)
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ap.add_argument("--xmax", type=float, default=50.0)
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ap.add_argument("--ymin", type=float, default=-100.0)
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ap.add_argument("--ymax", type=float, default=110.0)
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ap.add_argument("--osm", default=None,
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help="OSM extract; building outlines are cut out so rooftops never become terrain")
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return ap.parse_args(argv)
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def find_proj():
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import glob
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import shutil
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env = os.environ.get("PROJ_BIN")
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if env and os.path.exists(env):
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return env
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which = shutil.which("proj")
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if which:
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return which
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matches = sorted(glob.glob(os.path.expanduser(
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"~/.local/share/flatpak/app/org.qgis.qgis/x86_64/stable/*/files/bin/proj")))
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if not matches:
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raise SystemExit("no PROJ binary; set PROJ_BIN")
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return matches[0]
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def project_to_utm(points, proj_bin):
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app_files = os.path.dirname(os.path.dirname(proj_bin))
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env = dict(os.environ)
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env["LD_LIBRARY_PATH"] = f"{app_files}/lib:{env.get('LD_LIBRARY_PATH', '')}"
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payload = "\n".join(f"{lon:.9f} {lat:.9f}" for lat, lon in points) + "\n"
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out = subprocess.run([proj_bin, "+proj=utm", "+zone=11", "+datum=NAD83", "-f", "%.4f"],
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input=payload, capture_output=True, text=True, env=env, check=True)
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return [tuple(float(v) for v in line.split()) for line in out.stdout.strip().splitlines()]
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def building_polygons(osm_path):
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"""Building footprints as local X/Y rings, via PROJ into EPSG:26911."""
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nodes, ways = oc.load(osm_path)
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rings = []
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for _, tags, refs in ways:
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if "building" not in tags:
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continue
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pts = [nodes[r] for r in refs if r in nodes]
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if len(pts) < 3:
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continue
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rings.append(pts)
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if not rings:
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return []
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flat = [p for ring in rings for p in pts_flat(ring)]
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utm = project_to_utm(flat, find_proj())
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out, i = [], 0
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for ring in rings:
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n = len(ring)
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out.append([(utm[j][0] - ORIGIN_E, utm[j][1] - ORIGIN_N) for j in range(i, i + n)])
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i += n
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return out
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def pts_flat(ring):
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return ring
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def inside(x, y, ring):
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"""Ray casting point-in-polygon."""
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hit = False
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n = len(ring)
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for i in range(n):
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x1, y1 = ring[i]
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x2, y2 = ring[(i + 1) % n]
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if (y1 > y) != (y2 > y):
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xin = (x2 - x1) * (y - y1) / (y2 - y1 + 1e-12) + x1
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if x < xin:
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hit = not hit
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return hit
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def main():
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args = parse_args()
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entries, width, height, values = dem_stats.read_tiff(args.dem)
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scale = entries[33550]
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tie = entries[33922]
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e0 = tie[3] - tie[0] * scale[0]
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n0 = tie[4] + tie[1] * scale[1]
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sx, sy = scale[0], scale[1]
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nodata = None
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if 42113 in entries:
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try:
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nodata = float(entries[42113])
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except (TypeError, ValueError):
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nodata = None
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step = args.step
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cols = int((args.xmax - args.xmin) / step) + 1
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rows = int((args.ymax - args.ymin) / step) + 1
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print(f"grid {cols} x {rows} at {step} m over "
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f"X {args.xmin}..{args.xmax}, Y {args.ymin}..{args.ymax}")
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polys = []
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if args.osm:
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polys = building_polygons(args.osm)
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print(f"masking {len(polys)} building footprints")
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verts = []
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ok = []
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for r in range(rows):
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y = args.ymin + r * step
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for c in range(cols):
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x = args.xmin + c * step
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e, n = x + ORIGIN_E, y + ORIGIN_N
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col = (e - e0) / sx
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row = (n0 - n) / sy
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ci, ri = int(col), int(row)
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if ci < 0 or ri < 0 or ci >= width or ri >= height:
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verts.append((x, y, 0.0))
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ok.append(False)
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continue
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if polys and any(inside(x, y, ring) for ring in polys):
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verts.append((x, y, 0.0))
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ok.append(False)
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continue
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z = values[ri * width + ci]
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if nodata is not None and z == nodata:
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verts.append((x, y, 0.0))
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ok.append(False)
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continue
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verts.append((x, y, z - ORIGIN_Z))
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ok.append(True)
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faces = []
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skipped = 0
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for r in range(rows - 1):
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for c in range(cols - 1):
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i = r * cols + c
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quad = (i, i + 1, i + cols + 1, i + cols)
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if not all(ok[k] for k in quad):
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skipped += 1
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continue
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faces.append(quad)
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mesh = bpy.data.meshes.new("Terrain_DEM")
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mesh.from_pydata(verts, [], faces)
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mesh.update()
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obj = bpy.data.objects.new("Terrain_DEM", mesh)
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bpy.context.scene.collection.objects.link(obj)
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zs = [v[2] for v, good in zip(verts, ok) if good]
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print(f"vertices {len(verts)}, faces {len(faces)}, skipped cells {skipped}")
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print(f"Z range {min(zs):+.2f} .. {max(zs):+.2f} m (relative to origin ground {ORIGIN_Z} m)")
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# spot checks against the cross-section findings: gutters near +/-10.5 m
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for name, x, y in (("origin (Highland)", 0.0, 0.0),
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("Orange Dr end", -279.6, 0.0),
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("hero frontage", -133.0, -14.5),
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("north sidewalk", -133.0, 13.6)):
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if not (args.xmin <= x <= args.xmax and args.ymin <= y <= args.ymax):
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continue
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c = int((x - args.xmin) / step)
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r = int((y - args.ymin) / step)
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i = r * cols + c
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if ok[i]:
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print(f" {name:22} ({x:7.1f}, {y:6.1f}) -> Z {verts[i][2]:+.2f} m")
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out = os.path.abspath(args.out)
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os.makedirs(os.path.dirname(out), exist_ok=True)
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bpy.ops.wm.save_as_mainfile(filepath=out)
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print(f"saved {out}")
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if __name__ == "__main__":
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main()
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