Surveying Surveying A theodolite ( Amer. "transit") is an instrument for measuring both horizontal and vertical angles, as used in triangulation networks. It consists of a telescope mounted movably within two perpendicular axes, the horizontal or trunnion axis, and the vertical axis. These must be mutually perpendicular. The condition where they deviate from perpendicularity (and the amount by which) is referred to as horizontal axis error. ...more on Wikipedia about "Theodolite"
A total station is an optical instrument used in modern surveying. It is a combination of an electronic theodolite (transit), an electronic distance measuring device (EDM) and software running on an external computer. ...more on Wikipedia about "Total station"
In trigonometry and elementary geometry, triangulation is the process of finding a distance to a point by calculating the length of one side of a triangle, given measurements of angles and sides of the triangle formed by that point and two other reference points. ...more on Wikipedia about "Triangulation"
Trig points are triangulation pillars. In the UK they were erected by the Ordnance Survey. ...more on Wikipedia about "Trig point"
The Willamette Stone was a small stone obelisk originally located in the western hills of Portland, Oregon in the United States. It marked the intersection and origin of the Willamette Meridian and Willamette Baseline, which defined the grid system of sections and townships from which all real property in the states of Oregon and Washington has been measured following the Donation Land Claim Act of 1850. ...more on Wikipedia about "Willamette Stone"
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