A plane table (plain table prior to 1830^[1]) is a device used in surveying and related disciplines to provide a solid and level surface on which to make field drawings, charts and maps. The early use of the name plain table reflected its simplicity and plainness rather than its flatness.^[2]

History

The earliest mention of a plane table dates to 1551 in Abel Foullon's "Usage et description de l'holomètre", published in Paris.^[3] However, since Foullon's description was of a complete, fully-developed instrument, it must have been invented earlier.^[2]

A brief description was also added to the 1591 edition of Digge's Pantometria.^[3] The first mention of the device in English was by Cyprian Lucar in 1590^[1]

Some have credited Johann Richter, also known as Johannes Praetorius^[4], a Nuremberg mathematician, in 1610^[5] with the first plane table, but this appears to be incorrect.

The plane table became a popular instrument for surveying.^[2] Its use was widely taught. Interestingly, there were those who considered it a substandard instrument compared to such devices as the theodolite, since it was relatively easy to use.^[1] By allowing the use of graphical methods rather than than mathematical calculations, it could be used by those with less education than other instruments.

Plane table construction

A plane table cutaway.

This shows a plane table with part of the surface of the table cut away to show the mounting on the tripod. The mount allows the table to be levelled. On the table, the alidade with telescopic sight is seen

Use of a plane table

In use, a plane table is set over a point and brought to precise horizontal level. A drawing sheet is attached to the surface and an alidade is used to sight objects of interest. The alidade, in modern examples of the instrument a rule with a telescopic sight, can then be used to construct a line on the drawing that is in the direction of the object of interest.

By using the alidade as a surveying level, information on the topography of the site can be directly recorded on the drawing as elevations. Distances to the objects can be measured directly or by the use of stadia marks in the telescope of the alidade.

References

• Raymond Davis, Francis Foote, Joe Kelly, Surveying, Theory and Practice, McGraw-Hill Book Company, 1966 LC 64-66263

External links

• Telescopic Plane Table Alidade in the collection of the Smithsonian National Museum of American History. This image shows the bubble levels on the base.

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