A ranging pole — in Dutch and French a jalon — is a straight rod with a steel point, painted in alternating red and white bands from bottom to top. Surveyors and builders use it to set out sight lines and to make measuring points clearly visible over long distances. The strong colour contrast makes the pole stand out against any background.
How it works
You push the pole vertically into the ground at a known point. Sighting from a second point across two or more poles gives you a dead-straight line across the terrain (“ranging in”). That is how you set out the centre line of a wall, a trench or a road before digging or building starts. With optical instruments such as a theodolite or a level, the pole acts as a target.
Application
The ranging pole is part of the basic kit for setting out and surveying on site and in civil engineering. In practice you combine it with marker pegs, a tape measure or GPS.
Points to note
- Always set the pole truly vertical; a leaning pole introduces an error in the sight line that grows large over distance
- Make sure the pole stands firmly and cannot shift while you sight
Related terms
- Surveying
- Setting out
- Spirit level
- Property boundary
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