Special Publications Volume 85

Special Publications Volume 85

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Description

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1922 edition. Excerpt: ...the trace of these arcs. Their intersection depending on the accuracy of the estimate is a more or less accurate location of the point sought. With the plane table in approximate orientation, the triangle of error will be small and the point sought will lie close to this triangle. Hence only very short sections of arcs will be needed. Each short section will be controlled by the condition that it must pass through its appropriate vertex, and owing to this fact a sufficiently accurate control of its direction may be obtained by eye estimate. These short, lightly sketched arcs will usually intersect at the point sought cm first trial. After some practice in eye estimate of location of the circles, the sketching may be omitted and the point directly located by pencil dot. Orienting by estimation.--A small triangle of error is the result of a close orientation which the topographer endeavors to accomplish at the first trial by taking advantage of any range that may exist either of signals or other details already plotted on the sheet. It will serve the same purpose if they are near enough in line to estimate a direction on the sheet to the farthest object, and then to orient by it. The declinatoire may be used, but it is a slow and inaccurate method of orientation. It is employed for this purpose by placing the straight edge of the box containing the needle upon a magnetic meridian, previously traced upon the map, and revolving the table until the needle points to 0, or north, on the graduated arc at the end of the box. The magnetic meridian is roughly determined at any well-determined station, when the table is properly oriented by the use of the declinatoire itself, the meridian line being drawn upon the sheet along the straight edge of the...show more

Product details

  • Paperback | 24 pages
  • 189 x 246 x 1mm | 64g
  • Rarebooksclub.com
  • United States
  • English
  • black & white illustrations
  • 1236925963
  • 9781236925961