Transverse/offset survey
To survey the field ABCDE:
1. Choose any suitable diagonal,
ie AD
2. Measure the lengths along the
transverse line, ie AP, PQ, QR
and RD.
3. Measure the lengths of the
offsets, ie BQ, CR and EP.
Field diagrams
When in the field doing the survey
the surveyor sketches the
information as a field diagram.
To complete a field survey:
1. Start at one end of the
transverse line
2. Write down the cumulative
distances of the offsets from the
starting point
3. Write down the lengths of the
offsets.
4. Units are not shown.
20+27=47
Plane table radial survey
When doing a plane table radial survey you normally:
•Place a table towards the middle of a field
•Mark a point towards the middle of the paper.
•From this point draw a line towards each corner of the field
•Measure the distance from the point towards the middle of the paper
to each corner of the field
Note
•The angles at which the lines are drawn are important as this is used
in doing an accurate scale drawing,
•It is called a radial survey as all lines “radiate” out from the centre.
•The point O is often used as the centre point
Example 1
The diagram shows the results of a radial survey of a field ABCD
A
D
23m
87º 28m
19m 68º 81º 33m
C
O
B
Compass radial survey
A compass radial survey is similar to a plane table survey:
•Stand towards the middle of a field,
•Take a compass bearing of each corner of the field,
•Measure the distance from the point you are standing to each corner
of the field
Note
•Only very rarely is one of the corners directly north,
•Often the angle asked for involves the corners just to the left and
right of due north.
Example 2
The diagram shows the results of a radial survey of a field EFG
G 318º
N
E 053º
49m
29m
O
35m
F 197º
Today’s work
There are two ‘fields’ marked on the oval.
•Create a radial and compass survey/diagram of each of the
‘fields’.
•On ‘field 1’ use radiating lines (and protractors) and the
navigational compass.
•On ‘field 2’ use the giant protractor and the iphone.
•Use your surveys to find the area of the ‘fields’.
•Equipment: pencils, rulers, rubbers, paper.
Example 1
The diagram shows the results of a radial survey of a field ABCD
a) Find the size of BOC.
A
D
b) Calculate the length of BC.
c) Calculate the area of triangle OBC.
23m 87º 28m
a) BOC = 360  68  81  87
19m 68º 81º 33m
O
= 124º
C
x
B
b) a 2  b2  c 2  2bccos A
x2  332  192  2  33 19  cos124
Just type it in.
x2  2151  2
x  46  4m
c) Area = ½absinC
= ½  19  33  sin124
= 259·9m2
Example 2
The diagram shows the results of a radial survey of a field EFG
a) Find the size of GOE.
G 318º
N
b) Calculate the length of GE.
E 053º
c) Calculate the area of triangle GOE.
a) NOE = 53º
49m
NOG = 360  318
29m
= 42º
O
GOE = 53 + 42
35m
= 95º
b) a 2  b2  c 2  2bccos A
x2  492  292  2  49  29  cos 95
x2  3489  7
x  59  1m
c) Area = ½absinC
= ½  49  29  sin95
= 707·8m2
F 197º
Today’s work


Exercise 6G pg 197
#2a, 3a, 4, 5,