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Why did older surveying methods use observations of the Sun and stars?
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Figure 1: Photogrammetric photographs from two short, overlapping flight strips arranged for supplying mapping details. Photo-control points are shown on only one photograph; shading indicates a typical terrain feature such as a lake (see text).
In civil engineering and surveying, observations of the Sun and stars were historically essential for establishing precise geographic positions and orientation on the Earth's surface. Before the advent of modern satellite-based systems, surveyors used a theodolite equipped with a spirit level to measure the elevation angles of celestial bodies.1
These observations served several critical purposes:
- Positioning: By measuring the altitude of the Sun or known stars, surveyors could define lines of position on the Earth's surface. When multiple such lines were intersected, they provided a "fix" to determine the observer's location.1
- Geodetic Measurement: Celestial observations were fundamental to geodesy—the science of measuring the Earth's size and shape. By determining the angular height of a star from two different stations on the same meridian, surveyors could calculate distances and establish fundamental mapping grids.2
- Orientation: Because stars and the Sun provide fixed reference points in the sky, they allowed surveyors to determine true north and orient their work accurately, a practice dating back to ancient civilizations like Egypt.3
While these methods were once the standard for global positioning, they have been largely superseded by satellite technology, which offers greater efficiency and precision.1