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STADIA INTERVAL - 14071_156
DISTANCE   AND   ELEVATION   FOR INCLINED SIGHTS - 14071_158

Engineering Aid 2 - Intermediate Structural engineering guide book
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Figure 8-4.-(A) Angle of elevation and (B) angle of depression. The instrument constant is the same for all readings. Suppose  that  you  are  using  an  externally  focusing instrument  with  an  instrument  constant  of  1.0.  If  the stadia interval is 1 foot, then the horizontal distance is as  follows: h =  (100)(1)  +  1  =  101  feet. If the stadia interval is 2 feet, the horizontal distance is as  follows: h =  (100)  (2)  +  1  =  201  feet. Now  suppose  that  you  are  using  an  internally focusing  instrument.  In  this  case,  the  instrument constant is zero and can be disregarded. This is the advantage of an internally focusing telescope. So, if the stadia interval is 1 foot, the horizontal distance is simply the stadia distance which is 100 feet. For a stadia reading of 2 feet, the horizontal distance is 200 feet. Horizontal  distance  usually  is  stated  to  the  nearest foot.  Occasionally  on  short  distances  (under  300  feet), it maybe specified that tenths of a foot be used. Stadia Formulas for Inclined Sights.— -Most  often the sights needed in stadia work are not horizontal. It may be necessary to incline the telescope upward or downward at a vertical angle. This vertical angle (a) may  be  either  an  angle  of  elevation  or  an  angle  of depression, as shown in figure 8-4. If the line of sight is elevated above the horizontal, you speak of it as an angle of elevation.  If the line of sight is depressed below the horizontal, the vertical angle is an angle of depression. In either case, you find the horizontal and vertical distances by using the following formulas: These   two   expressions   are   called   the   stadia formulas for inclined sights in which h= v= h   = a  = f  +  c  = horizontal   distance vertical distance stadia  distance vertical  angle instrument  constant Refer to figure 8-5 for clarification of the terms in the  stadia  formulas  for  inclined  sights. Figure 8-5.-Stadia Interval—inclined sight. 8-5







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