SUMMARIZED SURVEY NOTES.
Definition of survey:
Survey refers to the science
of measuring and recording distances, angles and heights o the earth’s surface for the purpose of
producing maps or plans.
TYPES OF SURVEYING.
1.
Chain survey.
2.
Plane table survey.
3.
Prismatic compass survey.
1. CHAIN AND TAPE
SURVEY.
This is a simple land survey that deals with measuring and
recording linear distances on the ground.
EQUIPMENTS USED IN
CHAIN AND TALE SURVEY.
●
The chain:
It’s made up of steel wire with links which are
connected by small rings. Normally its length is about 20m or 30m long. It’s used for linear measurements.
●
The tape:
It’s made up of steel, strip or
fiberglass. Its length is about 10m to 20m. Also it’s having graduated divisions normally in 10mm. It’s also used to measure linear
measurements.
●
A peg:
It’s made up of wood or metal or
plastic material. Its about 50cm long. Its having a sharp point for easily
derivation into the land. Used to mark permanent position during survey.
·
Ranging rod or pole:
It’s made up of wood or
metal or plastic material. It’s about 2m to 3m long. It’s painted alternatively in red and white colors in order to be seen
clearly. They are having sharp points for easily derivation into the ground. It’s used to mark temporally points.
·
A surveyor’s band:
It’s made up of steel, strip or fiber glass and rolled into a metal frame with
a winding handle. It’s about 30cm long to
100cm.
·
Cross staff:
It’s made up of metal or wood with eye slits and right angles. It’s used to measure the right angles.
·
Arrow:
It’s made up of steel with one circular end. It’s tied with colored cotton
material easy to be seen. Used to mark points on the ground.
·
Notebook and pencil:
These are used to record
or booking all necessary information during chain survey.
METHODS INVOLVED IN CHAIN SURVEY.
·
The chain is thrown to be
extended.
·
A leader takes arrows
while followers take rods.
·
Follower erect a rod at
the first base point, places a brass handle of a chain against the rod.
·
A leader straightens a
chain and inserts an arrow to the end of a brass handle of a chain.
·
A booker books important
data.
·
A leader drags a chain so
that follower’s end is at the leader’s arrow.
·
The process becomes
repeated over and over until the survey reaches I’s climax.
USES OF CHAIN SURVEY.
·
To map a small area this
is flat or relative flat.
·
To add details the large
scale maps.
·
To find the linear
distances on the ground.
·
To find the area of a
given land.
·
It is used by land planners.
ADVANTAGES OF CHAIN SURVEY.
·
it is simplest and common
method or technique in survey of land.
·
Equipments used can be
replaced. Like a tape can replace a chain.
·
It does not involve
complicated mathematics.
·
it needs few people to
conduct i. e a leader and a follower.
·
The equipment used in
chain survey are simple and they do not involve much knowledge.
DISADVANTAGES OF CHAIN SURVEY.
·
It cannot be conducted in
a built area.
·
It is not easy undertaken
in density wooded areas.
·
It is inefficient in steep
areas.
·
It becomes difficult when
it faces obstacles.
·
It consumes time.
PRINCIPLES WHEN CONDUCTING CHAIN SURVEY.
o
Use few chain lines as
possible.
o
Avoid steep slope.
o
Keep chain lines short.
o
Select one major line
(major line).
o
Maintain all triangles
between 30 and 120 degrees.
ERRORS IN CHAIN SURVEY.
Errors in chain survey are
mistakes or short coming that happen during the survey process leading to
taking wrong measurements.
SOURCES OF ERRORS IN CHAIN SURVEY.
o
Poor reading from the
chain.
o
Fault in chain or any
chain equipment.
o
Laziness of the surveyor.
o
Sagging of a chain.
o
Incorrect positioning of
an arrow along the chain line.
WAYS OF AVOIDING ERRORS.
o
To read carefully from the
chain.
o
The surveyor should be
serious.
o
To avoid sagging of a
chain.
o
To select few chain lines
to avoid confusion.
o
To avoid a chain with a
fault.
2
PRISMATIC COMPASS SURVEY:
A prismatic compass survey
is a survey which employs prismatic compass to measure and record distances and
heights as well as bearings of an object.
Prismatic compass is a
prism like feature with a hinged lid, sighting slit and a glass prism.
HOW TO USE A PRISMATIC COMPASS.
o
Open the lid and flick up
the brass box containing glass prism.
o
Align the object with the
prism slit and the hairline on the glass lid.
o
A thin magnetic bar swings
toward the magnetic north.
o
Hold the compass properly.
PRECAUTIONS WHEN USING A PRISMATIC COMPASS.
§ Avoid a deposit of magnetic materials.
§ Hold a prismatic compass properly.
§ Avoid wearing a wrist(iron) watch.
§ Avoid a deposit of ferrous materials mainly that of iron.
ADVANTAGES OF A PRISMATIC COMPASS SURVEY.
v It is quick method in the field.
v It reduce errors than chain survey
v A check can be made on both forward and backward bearings.
v All readings can be made quickly and easily.
v It can be combined with other methods like chain survey nd plane table
survey.
DISAVANTAGES OF PRISMATIC COMPASS SURVEY.
v It requires areas with no ferrous materials.
v It requires areas with no magnetic materials.
v It requires high knowledge.
v It is difficult to hold a compass properly.
v It is geological knowledge.
3 PLANE TABLE SURVEY:
This is a survey which
deals with measuring ad recording of distances of object using a plane table.
The plane table is simple
wooden board about 70cm by 60cm by 1 cm with around brass screw. The following are its instruments:
v Tripod stand is three legged frame on which a table is mounted.
v Alidade is a brass ruler with graduated measurement.
v Plumbing fork is a bob used to fix a position exactly by pointing down over
the ground when it is tied to the clamping screw.
v Trough compass is a narrow wooden box containing a magnetic needle.
v Spirit level is an instrument used to insure that plane table surface is absolutely level.
v Clamp is an instrument used to board of a table in into a position.
ADVANTAGES OF PLANE TABLE.
a.
It is a quick method.
b.
It is accurate method.
c.
It is used to produce
immediate maps.
d.
The map is produced direct
and office work is out of the minimum.
e.
It can be carried out in
extremely areas.
DISAVANTAGES OF PLANE TABLE.
i.
It is not conducted during
rainy season.
ii.
It needs high knowledge
iii.
The scale of drawing is
limited by a size of a plane table.
iv.
It cannot be conducted in
areas with thick forest.
4
LEVELLING SURVEY:
Leveling may be defined as
the determination of the relative heights of various points on the earth’s surface.
EQUIPMENTS USED IN LEVELLING SURVEY;
i.
LEVELLING STAFF:
This equipment looks like
a big ruler about 4 meters long. Used to record differences in heights.
ii.
SPIRIT LEVEL:
This is the one of level
instruments used for generating horizontal line of sight. It is also used to
take readings from the leveling staff. The instrument is put on a tripod stand.
iii.
TRIPOD STAND:
This hold a spirit level
so that it can a sight a point horizontally.
iv.
ABNEY LEVEL:
This is used to measure
degrees, percent of grade, topographical elevation and a chainage correction.
SIGNIFICANCE OF LEVELLING:
a.
To determine the relative
heights of various points on the earth’s surface. These heights
can be used in the drawing of contour lines.
b.
Production of longitudinal
section of roads.
c.
Used to obtain concrete
cross sections of man made features at right angles to the longitudinal lines.
DISADVANTAGES OF
LEVELLING;
a.
Involves a lot of
movements from time to time especially when changing directions and distances.
b.
The datum line accuracy
sometimes is made difficult by reference points.
c.
Leveling by using abney
level is a very crude and laborious method.
PREPARED BY
Kim saeloum
