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Roman Surveying Technique 2 - The Groma

Written by: Stan Kitchener.

A line-of-sight surveying instrument, for straight roads or right angle construction.

Marine shield.
The DATUM-PEG is placed in the ground as the chosen starting point.

The GROMA is planted in the ground adjacent to the datum peg such that the DATUM-STRING `B. of the groma hangs vertically directly above the datum-peg.

The top cross of the groma is then point towards the desired direction of the road/wall/trench-line: viewing line `A., through `B. to `C..

A man with a RANGING POLE is directed, at a distance, to be in-line with the groma lines A., B. & C., and a STRINGLINE is then run along the ground between them. Then, without disturbing the groma top-cross, walk around to groma-line `D. and view line `D., through `B., to `E.

A man with a RANGING POLE is directed, at a distance, to be in-line with the groma lines D., B. & E., and a STRINGLINE is then run along the ground between them. This produces a RIGHT-ANGLE on the ground between the string lines.

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Groma