Cross Staff Survey
This
type of survey is undertaken to locate boundaries of a field or a field or plat
and determinations of its area.
type of survey is undertaken to locate boundaries of a field or a field or plat
and determinations of its area.
Principle:
The
principle of the survey is to divide the given area in to no of right angled
triangles and trapezoids and to calculate and plot the areas of triangles and
trapezoids.
principle of the survey is to divide the given area in to no of right angled
triangles and trapezoids and to calculate and plot the areas of triangles and
trapezoids.
Instruments/Material Required:
Two
Chains, arrows taps, ranging rods, cross-staff and drawing material
Chains, arrows taps, ranging rods, cross-staff and drawing material
Procedure:
Two
chains are usually provided one for measuring distance along the chain line and
other for measuring the offsets. The cross staff is used to set out the
perpendicular directions for offsets. In this survey, the base line runs
through the center of the area, so that the offsets are left or right side of
base line are fairly equal. To check accuracy length of the boundary lines may
also be measured. After the field work is over, the survey is plotted to a
suitable scale.
chains are usually provided one for measuring distance along the chain line and
other for measuring the offsets. The cross staff is used to set out the
perpendicular directions for offsets. In this survey, the base line runs
through the center of the area, so that the offsets are left or right side of
base line are fairly equal. To check accuracy length of the boundary lines may
also be measured. After the field work is over, the survey is plotted to a
suitable scale.
Calculations of Field Area:
By
this method of survey, the field as divided in to right angled triangles and
trapezoids are calculated as under:
this method of survey, the field as divided in to right angled triangles and
trapezoids are calculated as under:
- Area of right -angled triangle
= ½ base x Height. - Area of trapezoid= sum of
parallel sides/2 x Height.
Add
the areas of all the triangles & trapezoids and sum is equal to the total
of a field.
the areas of all the triangles & trapezoids and sum is equal to the total
of a field.
The computations for area should be written in a tabular from as given below.
TABLE
|
Serial
no. |
Figure
|
Chain age in m
|
base in m
|
Offset in m
|
Mean offset in m
|
Areas in m2 A=col.
4.xcol.6 |
|
1
|
2
|
3
|
4
|
5
|
6
|
7
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Total
|
|
m2
|
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