Surveying

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  • Topic: Telescope, Lens, Focal length
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LBYCIVB
EXERCISE No. 1
STADIA INTERVAL FACTOR

Student Name:____________________Date Performed: _____________ Group No.: ___________Date Submitted: _____________
Group Leader: _______________________Grade: ___________

1. Objective: The objective of this exercise is to determine the stadia interval factor of an engineer’s transit or theodolite.

2. Background:

The telescope of an engineer’s transit, theodolite, plane table alidade, and many levels are furnished with stadia hairs in addition to the regular cross hairs. One stadia hair, the upper cross hair, is above and the other, the lower cross hair, an equal distance below the middle cross hair.

The process of taking stadia measurements consists of observing, through the telescope, the apparent locations of the two stadia hairs on the rod, which is held in a vertical position. The interval thus determined, called the stadia intercept/interval/reading, is a direct function of the distance from the instrument to the face of the stadia rod.

The principle of the stadia method is based in Figure 2.3 shown, wherein the line of sight of the telescope is horizontal and the rod is vertical. For the notation

i = spacing between stadia hairs,
c = distance from the instrument center to the objective lens center, f = focal length (objective lens to focal point),
d = distance from the focal point F to the face of the rod, C = (f + c) = stadia constant,
• for internal focusing telescope, C = 0.0 and
• for external focusing telescope, C = 0.3 m
D = (C + d) = distance from the instrument center to the face of the rod, and S = stadia intercept or interval

Considering Fig. 2.3, by similar triangles,

f / i = d / S

The horizontal distance d, from focal point to the rod is

d = ( f / i )*S but K = f / i

therefore,
d = K S, Eq. (2.1)

where:K is the stadia interval factor

The horizontal distance D, from instrument center to rod is

D = K S + (c + f)
D = K S + C Eq. (2.2)

3. Instruments and Accessories

1 Engineer’s transit or theodolite
1 100-m tape
1 stadia rod
1 Set of marking pins
2 range poles

4. Location

DLSU football field or any level open surface

5. Procedure

a. Select a fairly level ground surface where a horizontal sight distance of up to 100 meters can be obtained. b. Drive a hub into the ground at one end of this distance and designate this as point O. A marking pin can also be provided on point O. c. Set up and level the engineer’s transit over point O. d. Establish a line of 100-meter distance starting from point O and place a marking pin on every 10-meter mark and designate this locations as points A, B, C, D, and E. Mark each point with a pin. e. With the stadia rod held vertical at each designated 10-meter marks, and with the telescope horizontal, obtain and record the upper and lower stadia hair readings. f. Compute the stadia interval factor, K, using the equation

K = (D – C) / S

6. Data

Stadia Constant ___________

|Station |Stadia Hair Readings (m) |Stadia Intercept |Stadia Interval Factor, K | | | |(m) | | |Occupied |Observed |Upper |Lower | | | |O |A | | | | | | |B |...
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