Monday, 21 December 2015

Basics of Surveying

Basics of Surveying
1)Definitions Surveying – the art of measuring distance and angles on or near the surface of the earth
Plane surveying – the land surface is considered to be a plane for all X
and Y dimensions, and all Z dimensions (height) are referenced to this plane. Most engineering surveys are plane surveys, those that cover long distances may need to correct for the earth’s curvature.
2)Equipment notebook – record all your data and sketches transit – used to establish straight lines and measure horizontal and vertical angles tape – measures distances
level rod – measures distances in
total station – electronic measuring
instrument that records and
processes field data.
prism rod – locates the points of
interest and reflect laser back to
total station for angle
and distance measurements.
engineer’s tape – measures the
height of the instrument (transit or
total station)
survey nails – locate points of
interest for future use
two-way radios – keeps contact
between the instrument person and
the rod person
One of the most important aspects of surveying is taking accurate, neat,
legible, and complete field notes. The degree of completeness comes from practice.
Details thatseem obvious in the field may be obscure back in the office a couple weeks later.
Sketches of your surveyed area will
also aid in comprehension and
ordering of the data.
These sketches do not need to be to
scale. Do not crowd your notes.
At a minimum, ALWAYS record the
instrument height, rod height,
occupying point,
backsight point, and datapoint
ranges in your notebook. Then, if
there was an error in
inputting the correct data into your
total station, you have a double
check. A description
and sketch of each surveyed point
are very useful as well.
2.2)Level Transit
we can determine the elevation
difference between
Points 1 and 2 as such:
Reading on Level Rod 1 from
horizontal line of sight = 2.63 ft
Reading on Level Rod 2 from
horizontal line of sight = 7.21 ft
Elevation Difference = 4.58 ft
The distance between the points can
be determined with a measuring
If elevation at the instrument is
Actual Elevation at Point 2 = Elev at
instrument + HI + LR1 Reading –
LR2 Reading
If elevation at Point 1 (backsight) is
Actual Elevation at Point 2 = Elev at
Pt 1 + LR1 Reading – LR2 Reading
2.3 Total Stations
A total station records and processes
all the data collected in the field. It
distances and angles by use of a
laser shot from the instrument and
reflecting prism on
the survey rod. A total station is
simply a computer. It can only know
what you input.
When you orient the total station
with a 3-D location and an angle at
each setup, it will
reference all ensuing point data to
2.3) Location
If there is a benchmark available
that has known XYZ coordinates,
then great, use that as
a setup or backsight point. Most sites that EWB work in will not have
benchmarks. You have two other options, and the choice depends on the level of detail needed in your
survey. If precise detail is needed,
bring an accurate GPS system with
you to locate your position. If relative detail is needed,
then enter any value for your
location and reference
everything to that point, i.e. label
your northing as 5000, easting as
10,000, and elevation
as 1000. If the precise coordinates
are not necessary, this latter option
may be easier to
perform in the field.
Just giving your total station a
location lets it know where it is, but
it doesn’t know where
it’s looking. So, you will have to
orient the instrument as well. The
options for doing
this again depend on the level of
precision needed for the project. For
accuracy and
precision, you can either bring a
compass that tells you which
direction is true north, or
you can shoot a second point that
has known XYZ coordinates. Again,
this latter one will
be very rare in most EWB locations.
If you bring a compass, then station
your prism rod
in the direction of true north and
shoot with the total station. The
instrument will then
know where it is and where it is
If precision is not necessary, you can make an educated guess as the
direction of north
(without the aid of a compass) and
shoot the prism rod. This will at least
orient your
instrument and the rest of your
points will be referenced to this
location and direction.
2.4) Leveling
For each setup, the survey
instrument must be level. The
locations and orientation
established above assume a level
instrument. The basic procedure for
tripod and
instrument leveling is provided
1. Center tripod over desired point
at an appropriate height and make
the base fairly level
2. Attach the instrument to the base
screw (Note: Do not let go of
instrument until the bottom screw
has been attached)
3. Turn on the instrument if using a
total station
4. Turn on the laser level or attach
5. Maneuver the tripod to center the
plumb on the control point
6. Coarse-level the instrument by
adjust the tripod legs individually
until the level
bubble is mostly centered (Note: this
adjustment will only minimally
adjust the location of the plumb)
7. To fine-tune the leveling, orient
the three black fine-tune level knobs
(at base of instrument) as a triangle
with a point facing away from you
a. Adjusting the two closest to you at the same time, turning them both
inward will move the bubble to the
left. Turning them both outwards
will move the bubble to the right.
b. Adjusting the knob away from
you, turning it counter-clockwise will
move the bubble away from you.
Turning it clockwise will move it
towards you.
8. After instrument is level, check
location of plumb. If you are within
a couple of inches, you may move the instrument by half-unscrewing the bottom screw and sliding the
instrument into place. If you are too
far off, then you will have to move
the whole tripod into position.
9. Repeat until the instrument is
level and over the correct point.
2.5) Viewscope Orientation
If you are using a total station,
sometimes it may not be obvious as
which way is up for
the survey gun. The correct
orientation has the horizontal fine-
tune knob on the lower
right and the vertical fine-tune knob
on the upper left as you are sighting
through the
instrument. Running the instrument
upside-down will invalidate your
2.6)Moving the Instrument
When you shoot a point to use as
your next location, place a nail or
some other relatively stable marker in the ground. Move the instrument to the new nail. When setting up the
total station, tell the instrument which point you are on. Since you
have already shot this
point, it knows its location. Backsight to another control point, and the instrument will
now be correctly oriented and ready
to continue on. Be sure to check your error after the backsight. If it is large, there might have been a mistake in some previous measurement that you’ll need to double check.
3) Point Descriptions Be consistent with point descriptions. Label all your control points the same, i.e. do not label them as “control1”, “control2”, etc. Label them all as “control” (or some variation thereof) and let the point ID number
be the differentiating factor between
The importance of these distinctions will become apparent if you are using a CAD program afterwards to draw up your survey points, since each point descriptions will become its own layer in the program.

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