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Contours, spot elevations and slope labels

Get contours onto the drawing, label them, and read elevations off the surface.

4 min read

Contours

  1. Surfaces → Contours.
  2. Set the interval, the base elevation, and how often a major line falls, every fifth, say, or every tenth.
  3. Name the minor and major layers, or name them the same to keep everything on one.
  4. Generate. They arrive as real entities, each layer coloured, weighted and styled the way the surface's contour style says.

A contour is the exact intersection of the triangulation with a level plane. It is not sampled or approximated, so a contour that touches a spot elevation touches it exactly.

Styling them

On the Surfaces tab, Contours on the map is where a surface's contours are styled: the interval (or leave it to choose one from the surface's range), the base elevation, a major line every Nth minor, and for each class its colour, pen weight, line style and whether the elevation is written along it. Apply keeps it with the surface, and the canvas redraws at once.

  • The canvas, Generate contours and the plotted sheet all draw from the one style, so what you see is what leaves.
  • Pen weights are millimetres on the sheet, the ISO set from 0.13 to 1.0.
  • Smoothing lives here too. It is display only: a smoothed line no longer sits exactly on its level, and nothing measured reads a contour.

Labelling them

  • Contour labels repeat the elevation along the line the way a topo sheet reads.
  • Slope labels state the grade between two picked points on the surface.
  • Both plot the right way up, whichever direction the line runs.

Spot elevations

Drop a spot elevation and it interpolates within the triangle that contains it. Ask outside the surface and Backsight refuses rather than extrapolating, a height beyond the data is not a measurement.

Points on a surface

Points on a surface puts a point at every vertex, or at an interval along a line, at the surface's elevation there, the quick way to get design or existing-ground elevations onto a line of chainage.

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