RECIPROCAL LEVELING
Reciprocal leveling is employed to determine the difference
in elevation between two points when it is difficult or impossible to keep
backsights and foresights short and equal
in elevation between two points when it is difficult or impossible to keep
backsights and foresights short and equal
In this method, two sets of rod readings are observed, (1)
one set is taken with the instrument set up close to one point, and (2) another
with the instrument set up close to the other point.
one set is taken with the instrument set up close to one point, and (2) another
with the instrument set up close to the other point.
Considering the Figure 1 below, the equations to obtain the
difference in elevation are the following
difference in elevation are the following
DEA
= (a – b) and DEB = (a’ – b’)
= (a – b) and DEB = (a’ – b’)
TDE = (DEA
+ DEB)/2 = [(a – b) + (a’ – b’)]/2
+ DEB)/2 = [(a – b) + (a’ – b’)]/2
Elev. BM2 =
Elev. BM1 ±
TDE
Elev. BM1 ±
TDE
where:
DEA =
the mean difference in elevation between A and B with level at left
the mean difference in elevation between A and B with level at left
DEB =
the mean difference in elevation between A and B with level at right
the mean difference in elevation between A and B with level at right
TDE = the true mean
difference in elevation between A and B
difference in elevation between A and B
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Procedure:
- Set
two hubs either on the 2nd or 3rd floors of the
Velasco and
these the BM1 and BM2, respectively. The elevation of BM2 is to be
determined while the elevation of BM1 is known or assumed to be 10.000
meters above see level. Also, imagine that the football field between the
Velasco and
intervening deep ravine or wide river. - Set
up and level very carefully the instrument at point A at Velasco Building
(3rd floor) near BM1. - Take
and record a series of three consecutive backsight rod readings on BM1 and
six consecutive foresight rod readings on BM2. - Move
the instrument to point B at
Building (3rd floor) which is on the opposite side of the
imaginary ravine and near BM2, set up, and level the instrument carefully. - From
the new set up, take and record three consecutive foresight rod readings
on BM2 and six consecutive backsight rod readings on BM1. - Tabulate
observed and computed values accordingly. Refer to the accompanying sample
format for the tabulation of field data.
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Instrument Set
Up Near BM1 |
Instrument Set
Up Near BM2 |
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Station
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B.S.
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F.S.
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Station
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F.S.
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B.S.
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BM1
(a)
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BM2
(b’)
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BM2
(b)
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BM1
(a’)
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Sum
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Sum
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Mean
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Mean
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