Military surveying and field sketching by William Hamilton Richards

Author:William Hamilton Richards
Language: eng
Format: epub, pdf
Published: 1875-03-25T05:00:00+00:00

"^^^ j GtoA ... 39° 16'

AtF fromHtoA . . . 38° 40'

This last observation is taken in order to apply the angular test, if the line F H, when laid down on the plan, be found to pass through H, already fixed, we may conclude that no great error has taken place in observation or construction.

When a Station is fixed by an acute intersection, its position should be verified by several observations in this way.

As the third angle of any triangle is the supplement of the others, it is immaterial which two angles we observe, and it occasionally may save time to observe the second angle at the vertex in preference to the other end of the base. For instance, in the triangle A B D, ^jg, 45^

having observed at one end of the base the angle D A B = 49° 6', we might find it convenient to observe the second angle at D 50° 20' instead of at the other end of the base B.

Then A B D is known 180° - (50° 20' + 49° 6')=80° 34'. ^^ ^B

When it is intended not to calculate the length of the sides of the triangles, it may sometimes be convenient to measure the angular distance from some Station already fixed, although belonging to a different triangle, and although the resulting figure may not be a triangle.

For instance, when at E, (Plate XII.) wishing to observe the direction of F and G, we might find it easier to observe the angles between these points and H, instead of A, if the latter be obscure, or not in the same horizontal plane.

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