welcome students this is the twenty fifth
lecture on digital land surveying and mapping
in today's lecture i am going to discuss on
ah different errors in total station now this
lecture will be discussed under following
heads introduction followed by the calibration
and then the different errors in total station
followed by summary for the reading and review
questions now you know that there are three
axis that is available in total station one
is that horizontal axis then vertical axis
horizontal axis vertical axis 
and ah line of collimation of axis of sight
line of sight or side axis so these are the
three axis already i had discovered that the
line about which our telescope rotates that
is the horizontal axis and the line about
which our home photo station rotates in the
horizontal plan that is the vertical axis
when perfectly centered level and the line
of along which we do see the object that is
the line of sight now this line of sight should
be perpendicular to horizontal axis horizontal
axis then you're our horizontal axis should
be perpendicular to vertical axis as well
as our line of sight also should be perpendicular
to the vertical axis so these are the three
the conditions which any total station should
satisfy and then we call that the instrument
is permanently adjusted and this three condition
had to be satisfied by the total station before
we start taking the observation so this is
the pre requisite condition to make use of
our conversation that our horizontal axis
should be perpendicular to the vertical axis
our line of sight should be perpendicular
to the horizontal axis and also line of sight
should depend on the vertical axis
and this is the ideal condition but practically
hardly we find that our instruments are exactly
permanently adjusted so we need to ah take
care if there is any ah lock in permanent
adjustment or not if there is any lock in
just permanent adjustment that leads to some
errors so that is what we will be discussing
today and ah it has been found that ah if
we go for ah both face observation that means
our direct mode and reverse mode so like direct
mode is this one and if we see this one is
the reverse mode so we will have we have an
a if we take the average of these two reading
then mostly ah most of the errors can be avoided
but unfortunately in the field hardly we go
for both mode of observation because of limited
now you can see in this instrument also if
i want to take measurement from this side
i will not be able to take because i do not
have the data collector this side so ah due
to limitation of the instruments also due
to various other reason generally we do not
go for both face observation in total station
or we can say in the industry single face
observation are most rampant so we need to
know very well what are the different types
of errors arise out of the lock in permanent
adjustment of the instruments the errors that
arises due to lack in permanent adjustment
of the instrument can be measured and then
taken care of through a process called calibration
so first we need to say what about calibration
actually whenever we use our instrument or
whenever there is a difference in temperature
that means there is a fluctuation of temperatures
or whenever we transport the instrument from
long distance ah and about ah their re permanent
adjustments of the instrument gets changes
also the calibration parameter of that means
the calibration parameter of the instruments
gets changes due to mechanical shock temperature
change rough handling etcetera and that those
parameters has to be recalibrated and has
to be ah fed to the instrument so that during
our observation it takes care of those parameters
automatically so and that can be done some
by making use of some standard calibration
process that is available and we should go
for calibration of the instrument before we
start the instrument in the beginning that
means when we had purchased a new instrument
to start observation with instrument we should
go for calibration now if we want to use the
instrument after long stage that means for
a long time if we have not used the instrument
then ah we should go for calibration before
we start to use if we transport the instrument
for a long distance there may be some [large/jerk]
jerk or of ah transportation so we should
go for calibration then if we in the field
also if we see that there is a large fluctuation
of temperature then also we should go for
calibration and more specifically when we
want to go for very precision walk we should
go for calibration
now one thing has to be remembered that before
we calibrate the instrument that temperature
of the ah instruments should be maintained
it's combined temperature that mean temperature
at which it functions properly now range calibration
has been done those parameter will be uploaded
inside this software automatically and the
software will take care of these parameters
ah of its own so calibration process also
done once it is done it will be automatically
taken care of by the instrument now due to
the lack in permanent adjustment of the instrument
that is if the horizontal axis is not perpendicular
to vertical axis if the line of sight is not
perpendicular to horizontal axis or vertical
axis then there are different types of error
that will come across and also some other
error that will come in total station like
[hori/horizontal] horizontal collimation error
tilting axis error vertical collimation error
compensator index error eccentricity error
circle graduation error collimation laser
of laser pointer error these are the main
errors which generally we find with the total
station and we are too taken care of these
errors primarily now you take care of these
errors actually we should regularly calibrate
our instrument preferably in the field before
we go for any measurement and that will reduce
or eliminate most of these errors in our measurement
now the horizontal collimation error horizontal
collimation error it is when the line of collimation
a line of sight line of sight is not not perpendicular
to horizontal axis that means ah if i this
is the telescope this is the line of sight
will be passing through this and if this line
is not perpendicular to the horizontal axis
then ah horizontal axis will be like this
and our collimation axis should be perpendicular
if it is not done suppose it is inclined so
if it is inclined then there will be some
axial rotation so this is our horizontal axis
about which our telescope is rotating and
this is our line of sight line of sight so
line of sight is not perpendicular then we
have the error like this this is called axial
error and due to this axial error the the
reading in horizontal circle horizontal circle
reading will be affected
so horizontal circle reading means we'll get
wrong horizontal angle so if we ah get the
mistakes or wrong of these there is error
in horizontal angle then that will lead to
error in position as well as other parameters
now [this/these] error will be severe if the
line of sight is stiff that means if i say
like this or like that so that will be our
still severe now as i told you that if yeah
if we take both phase measurements so ah like
this is the face like measurement or yours
sight reveres mode and if we take the left
or you can in case of total station we will
say that the original mode or then if we take
these this mode as well as this mode measurement
and if we take the average of that that means
both face left and face right condition then
that average will provide us with eliminate
these errors so if we if the face that condition
our line of sight is like this and in phase
right condition the line of sight will be
like this so this will cancel each other in
the ah horizontal angle measurement where
we will take the average ah so this is the
idea behind the ah line of collimation horizontal
collimation error but as i told you in the
industry or in the ah in use of total station
the use of single phase measurement is rampant
so ah we need to take care of it through calibration
through calibration we can through calibration
ah we do find out the value of c the angular
error in axial angler error axial angular
error
and that had that can be that will be made
available in the total station and the software
will take care of it should be within certain
limit so in the manual it will be written
what is the limit which is permissible now
if this limit if the calibrated [mesur/measured]
measured value if the measured value of c
is greater than permissible limit permissible
limit of the instrument then we should send
our instrument to the manufacturers to make
this ah correction in the ah laboratory or
in their ah factory so that's all about horizontal
collimation error next [the/they] tilting
axis error tilting axis error now this is
these happens when the horizontal axis is
not perpendicular to vertical axis that means
our this axis is not perpendicular to this
so the vertical axis plumb line plumb line
and the horizontal axis is this one so if
it is not if the horizontal axis is not perpendicular
to vertical axis then it will cause the cause
the cause the plane of the line of sight plane
of line of sight 
inclined as we plan that means if we make
keep this ah ah telescope horizontal then
there is no problem but if we want to see
this above or below then this this twenty
axis error will cause a reading loss or error
in error in horizontal angle cause the plane
of line of sight inclined that will lead you
to error in horizontal angel horizontal circle
reading
now they say these are also can be eliminated
by taking the both phase measurement and taking
the average however of this again as the single
phase measurement is rampant we need to measure
the tilting axis ah tilting axis inclination
so b this value again has to be computed using
calibrated through a calibration we have to
measure and once it is measured then we will
we can get this to the ah computer software
which will automatically taken care of again
similarly if this value is axis the if the
measure value of the ah tilting axis interaction
is more than the ah permissible value then
we have to send again this instrument to the
manufacturer
now third error is vertical collimation error
vertical collimation error now as we know
that when the instrument is properly leveled
then our vertical circle remains in a vertical
plane so ah our that zero degree and one eighty
degree line of the vertical circle should
be in a vertical line in a vertical now if
it fails if the zero degree one eighty degree
is not vertical then vertical collimation
error comes so as a result of this the vertical
circle reading error in vertical circle reading
it leads to error in vertical circle reading
and ah so again same thing again this can
be ah reduced or eliminated by making use
of ah both face both face measurement and
taking its average we can and average provides
the we can eliminate or reduce but as the
single face measurement is one point also
we need to find out this collimation error
angle what is the angle of inclination of
this with with vertical so see suppose it
is a so this angle of inclination has to be
measured using calibration measured by through
a calibration and [may/made] made available
to the software to do this very correction
whenever we go for our ah vertical angle measurement
and again a if it exceeds the permissible
limit we should send this instrument to the
ah manufacturer for necessary corrective measures
next the compensator index error now as we
know that each of this instrument is provided
with some compensators so that compensator
compensates the leveling that was whenever
we do carry out the leveling and centering
operation there is always some residual leveling
error which we do finally carry out the leveling
using the electronic compensator instrument
like so here you can see that there are two
come one original and another ah one compensator
will indicates in this direction another in
this direction so we can it y and x so there
are two compensator generally we had which
we do make ah adjusted at to by playing this
thing to ah get provide has the exact ah leveling
of the instrument there is always some error
associated with the compensator one in the
longitudinal level another in the transverse
direction so suppose l is the error in the
longitudinal direction and t is the error
in the transverse direction and these two
longitudinal and transverse error of the compensator
index is also known as zero point errors
now these error also can be eliminated by
taking the both face measurement however this
because ah for single face measurement also
we need to know these errors and these errors
can be also be find out by through calibration
or and if the limit exceeds then we should
go for ah sending the instrument to the factory
so next collimation of laser pointer so whenever
we use laser pointer in a reflector less measurement
collimation error collimation error or in
laser pointer now we know that a in case of
a ah reflector less measurement reflector
less ah measurement ah what we do ah in in
inside the telescope this is the eye piece
and this is the objective lens and the line
joining the center of this and the center
of this that is called line of collimation
or line of line of collimation line of collimation
and also there is a reticule and the center
of this is if it passes through this this
is called from here it is called line of sight
so in ideal case line of collimation line
of sight and line of collimation are identical
a that is the condition we require for our
observation using telescope now apart from
the now whenever there is a reflector unless
measurement actually you will see that there
is a guided path through which the laser beam
we send the laser beam to strike the target
now if you say this total station we can will
find that here there is a mark like this which
is the location for this is the this is the
location for laser guidance now the center
of that laser guidance laser guidance should
be the center of this laser guidance and the
center of the optical lines should be identical
that is the requirement
now in ideal case they are considering but
sometimes the center of the ah laser guide
or ah in the center of the objective lens
do not coincides due to this there is a ah
error of collimation of laser pointer now
because our instrument take gets the measurement
by the laser beam so say here we assume that
the direction of the laser beam is the in
direction of the line of sight direction of
the line of collimation now if there is any
ah discrepancy between this is the line of
collimation on if it is this is the laser
beam this is the laser beam and all the measurement
which is done with respect to this but it
is coming to reticule here so there will be
some error and that error ah causes errors
in both circles of measurement in order to
have a this error we need to we can also do
the ah both face measurement and taking the
average however for a single face measurement
again this derivation can be found out through
a calibration and that has to be stored in
the instrument so these are the fundamental
errors that is associated with the total station
instrument apart from that there are two errors
like already we have discus that there are
two types of circles one is the ah horizontal
circle in this and there is a pair of vertical
circle here and the whether it is horizontal
circle or is a vertical circles the center
of this the geometric center of this circle
may not coincide with the center of the rotation
so if there is a discrepancy between the geometric
center of the circle geometric center of the
of circle and the and center for rotation
they should coincide but if there is a discrepancy
between these two then that eccentricity error
comes of course these eccentricity error is
also not much because it is within the ah
instrument and but this can be avoided by
again by taking the average of measurements
on opposite sides of the circle so we should
try to take the ah measurement ah some measurements
in this side and some measurement in this
side so if we take the measurement in both
sides or some measurement this side some measurement
this side so then we can help we can ah taking
the average we can eliminate or minimize this
error another error is that that is a circle
graduation error so this type of error generally
arises a low cause of total stations where
these graduation may not be very ah fine or
precise so and there may be very minor deviation
in the measurements at some location so that
will arise the circle graduation error and
these ah error may be horizontal circle as
well as in the vertical circle and generally
we should take measurement at defined location
of the of the circles like so and then ah
we can a minimize or eliminate
so with this i like to ah conclude this class
because ah there are of course there are many
other errors which i will be taking up in
the my next class so finally i have discussed
in this class about the errors associated
with the total station when there is a lock
in permanent adjustment of the total station
however most of the errors that arises out
of the lock in permanent management can be
avoided by taking the ah both face measurement
and the average of them however in the industry
the single face measurements are rampant so
we need to go for finding out the measure
we have need to measure as well as to remove
those errors and that can be done through
calibration process and before doing any significant
work or any precise work we should go for
calibration of the instrument with this i
like to conclude this class next class will
be on other errors in total station
thank you
