zwitschi
6cded45e2a
Gutters sit at -10 m south and +10..12 m north, a ~2% crown between them, and the envelope runs 0.6-1.0 m per section. Gutter spacing independently confirms the 20.9 m carriageway measured from the crossing. The sharpest breaks are 0.09-0.12 m/m, so 3DEP does not resolve a kerb upstand: kerb height stays a recorded assumption rather than a derived value.
3.0 KiB
Cross-sections — crowned road, gutters, sidewalk shelves
Sampled 2026-11-06 from the local 3DEP DEM (Geo/raw/dem-3dep-1m-26911-2026-11-06.tif) with Geo/scripts/street_section.py. Seven sections at 40 m spacing, offsets −18 m to +18 m from the boulevard centreline (negative = south), 1 m sampling step.
What the profile shows
Every section has the same shape:
- a local low at about −10 m (south gutter),
- a rise to a flat-ish crown around +2 to +8 m,
- a second low at about +10 to +12 m (north gutter),
- then the north side climbing to the building line.
Those gutter positions bracket a carriageway of roughly 20–22 m, which independently matches the 20.9 m measured from the mid-block crossing in 2026-11-06-street-profile.md. Two unrelated measurements agreeing is the strongest evidence in the geo work so far.
Section table
| Along block | Lowest point | Road crown | Cross-fall across the road | Gutter candidates |
|---|---|---|---|---|
| 0.0 m | 118.78 @ −10 | ~119.41 @ 0 | ~0.6 m / 2 % | −10, +10 |
| 40.0 m | 118.43 @ −11 | ~118.94 @ 0 | ~0.5 m / 2 % | −11, +10.5 |
| 80.0 m | 117.84 @ −10 | ~118.33 @ 0 | ~0.5 m / 2 % | −10, +10.5–11.5 |
| 120.0 m | 117.22 @ −10 | ~117.73 @ 0 | ~0.5 m / 2 % | −10, +11.5 |
| 160.0 m | 116.55 @ −10 | ~117.04 @ 0 | ~0.5 m / 2 % | −10, +11.5 |
| 200.0 m | 115.96 @ −10 | ~116.37 @ 0 | ~0.4 m / 2 % | −10, +10.5–11.5 |
| 240.0 m | 115.63 @ −10 | ~116.02 @ 0 | ~0.4 m / 2 % | −10, +10.5–11.5 |
Total envelope from the lowest south gutter to the highest north point is 0.6–1.0 m per section, depending on how far the north sidewalk has risen.
Kerbs are not in the DEM
The sharpest breaks found at the expected kerb offsets are 0.09–0.12 m/m slopes — that is a gutter transition spread over a metre, not a kerb upstand. 3DEP is bare-earth and smooths a 0.15 m vertical step at 1 m sampling, so the DEM cannot give kerb height.
Consequence: kerb height and shape are an assumption until measured or observed in the reference photography. Write the assumption down where it is used rather than burying it in the mesh. Do not infer a kerb from the DEM's gradient.
What the demo ground mesh must do
- Crown the road at roughly 2 % from each gutter to the centre, not a flat plane and not a constant tilt.
- Step down into the gutters at about ±10.5 m from the centreline, then run the sidewalks at their own grade.
- The north sidewalk sits higher than the road crown and keeps rising toward the building line, so the two sidewalks are not mirror images.
- Crossing ramps must be modelled deliberately at the three crossings; nothing in the DEM supplies the local ramp geometry.
Open
- Kerb height, kerb radius, and ramp slope: assumption until surveyed or measured from photographs.
- The 200 m section peaks at +14 m rather than +18 m, which may be a tree canopy or a building edge in the DEM. Do not treat it as a road feature.
- Drainage inlets, driveway aprons, and pavement joints are not in this data.