Profiles (vertical alignment)
The road's elevation along its centreline — straight design grades joined by parabolic vertical curves, drawn over the existing ground.
The Profile tab
Select an alignment and open the Profile tab. Station runs along the horizontal axis, elevation up the vertical axis. It shows:
- the ground line — the existing surface sampled along the alignment,
- the design profile you author (grades + vertical curves),
- cut/fill between them, and a station band.
VPIs and vertical curves
A vertical alignment is a list of VPIs (Vertical Points of Intersection) — each a station, an elevation and a curve length. Straight grades run between VPIs; at each interior VPI a symmetric parabolic curve of the given length smooths the grade break: half its length before the VPI (the VPC), half after (the VPT). A curve length of 0 is a sharp grade break.
The Profile Builder dock
One row per VPI. Columns:
| Column | Editable? | Meaning |
|---|---|---|
| # | no | VPI number (1-based). |
| Station (m) | yes | Chainage of the VPI. |
| Elevation (m) | yes | Design elevation at the VPI. |
| Curve L (m) | interior only | Vertical-curve length; first/last VPIs are locked to 0. |
| Grade In % | no | Incoming grade (“—” at the first VPI). |
| Grade Out % | no | Outgoing grade (“—” at the last VPI). |
| K | no | L / |grade change| (“—” if undefined). |
- Add VPI — appends a VPI 100 m past the last (clamped to the alignment end), at the previous elevation, curve 0. The first VPI lands at the alignment start, elevation 0.
- Remove VPI — deletes the selected row.
- You can also place, drag and snap VPI grips directly in the Profile canvas; clicking a VPI selects its row and vice-versa.
Every edit is undoable and immediately re-elevates the corridor in 3D.
Design checks
Crest and sag curves are checked against the minimum K for the active standard and speed; a grade break with no curve is also flagged. Issues appear in the Design Issues dock.
- Crest K comes from the stopping sight distance and the driver eye / object heights (you must see over the summit).
- Sag K comes from the headlight criterion (your beam must reach far enough at night).
Both formulas are in the Formula reference.