the establishment of two - or three dimensional control network is the most fundamental operation in the surveying larg or small areas of land . control networks comprise a series of points or positions which are spatially located for the purpose of topographic surveying .
for the control of supplementary point , or dimensional control on site
the process involved in carrying out the surveying of a
area , the capture and processing of the field data .
and the subsequent production of a plan or map
, will now be outlined briefly.
the first and obvious step is to know the purpose and
nature of project for which the surveys are required in
order to assess the accuracy specifications , the type of
equipment and surveing processes involved
for example , a major construction project may require
structures , etc , to be set out to subcentimetre accuracy
, in which case the control surveys will be required to
an even greater accuracy .
earthwork volumes may be estimated from the final
plans , hence contours made need to be plotted at 2 m
intervals or less groud , thus indicating the accuracy of
the final process of topographic surveying from the
supplementary control and implying major control to a
greater accuracy .
the location of topographic surveying from the
supplementary control and implying major control to a greater accuracy .
the location of topographic surveying from the
supplementary control and implying major control to a
greater accuracy .
the location of topographic surveying from the
supplementary control and implying major control to
greater accuracy .
the location of topographic data may be done using total
station . GPS satellites is closely linked to the contour
interval required and the number of observations
required
the duration of the project will affect the design of
survey stations required for the control point a project of
limited duration may only require a long , stout wooden
peg, driven into solid , reliable ground and surrounded
by a small amount of concrete ,
a fine nail in the top defines the geometrical position to
be located .
the next stage of the process is a detailed
reconnaissance of the area in order to establish the best
position for the control points.
initially , data from all possible sources should be
studied before venturing into the field . such data would
coprise existing maps and plans , aerial photographs
and any previous surveying data of that area .
longitudinal section may be drawn from the map
contours to ensure that lines of sight between control
point are well above ground level and so free of shimmer
or refraction effects.
if the surveys are to be connected into the national
survey of the contry (ordnance survey national grid in the uk )
then the position of as many national survey point as
possible , such as (in the uk) those on the GPS active or
passive network . should be located . these studies ,
very often referred to as the , paper survey , should then
be followed up with a detailed field reconnaissance .
this latter process locates all existing control in the area
of interest both local and national and establishes the
final position for all the new cotrol required these final
positions should be chosen to ensure clear
uninterrupted lines of sight and the best observing
positions the location of these point and the type of
terrain involved , would then influence the method of
survey to used to locata their spatial position
indicates control points A,B ,,,F , in the area to be surveyed it, is required to obtain the coordinate position of each point , this could be done using any of the following methods :
a-intersection or resection
b-traversing
c-networks
d-GPS satellites
illustrates possible line of sight , all the horizontal angles shown would be measured to the required accuracy to give the shape of the network , at least one side would need to be measured , say AB ,
to give the or scale or size of the network ,by measuring a check baseline , say ED , and comparing it with its value ,computed through the network ,the scale error could be assessed ,this from of survey is classical triangulation and although forming the basis of the national maps of many countries is now regarded as obsolete because of the need for line of sight between adjacent point , such control would now be done with GPS
if the lengths of all the sides were measured in the same triangular configuration without the angles , this technique would be called,,trilateration,, Although giving excellent control over scale error ,swing errors may occur, for local precise control surveys the modern practice therefore is to use a combination of angles and distance ,
measuring every angle and every distance ,including check sight wherever possible ,would give a very strong network indeed using sophisticated least squares software it is now possible to probably the most favoured simple method of locating the relative coordinate positions of control points in engineering and construction is traversing ,
illustrates the method of traversing to locate the same control point A to F , all the adjacent horizontal angles and distance measured to the accuracies required resulting in much less data needed to obtain coordinate accuracies comparable with the previous methods ,
also illustrated are minor or supplementary control pint a,b,c,d located with lesser accuracy by means of a link traverse , The field data comprised all the angles as shown plus the horizontal distance Aa,ab,bc,cd and DB the rectangular coordinates of all these point would of course ,be relative to the major control
whilst the methods illustrated above would largely supply a two - dimensional cordinate position , GPS satellites could be used to provide a three- dimensional position
all these methods , including the computational processes ,are dealt with in later chapters of this book
indicates control points A,B ,,,F , in the area to be surveyed it, is required to obtain the coordinate position of each point , this could be done using any of the following methods :
a-intersection or resection
b-traversing
c-networks
d-GPS satellites
illustrates possible line of sight , all the horizontal angles shown would be measured to the required accuracy to give the shape of the network , at least one side would need to be measured , say AB ,
to give the or scale or size of the network ,by measuring a check baseline , say ED , and comparing it with its value ,computed through the network ,the scale error could be assessed ,this from of survey is classical triangulation and although forming the basis of the national maps of many countries is now regarded as obsolete because of the need for line of sight between adjacent point , such control would now be done with GPS
if the lengths of all the sides were measured in the same triangular configuration without the angles , this technique would be called,,trilateration,, Although giving excellent control over scale error ,swing errors may occur, for local precise control surveys the modern practice therefore is to use a combination of angles and distance ,
measuring every angle and every distance ,including check sight wherever possible ,would give a very strong network indeed using sophisticated least squares software it is now possible to probably the most favoured simple method of locating the relative coordinate positions of control points in engineering and construction is traversing ,
illustrates the method of traversing to locate the same control point A to F , all the adjacent horizontal angles and distance measured to the accuracies required resulting in much less data needed to obtain coordinate accuracies comparable with the previous methods ,
also illustrated are minor or supplementary control pint a,b,c,d located with lesser accuracy by means of a link traverse , The field data comprised all the angles as shown plus the horizontal distance Aa,ab,bc,cd and DB the rectangular coordinates of all these point would of course ,be relative to the major control
whilst the methods illustrated above would largely supply a two - dimensional cordinate position , GPS satellites could be used to provide a three- dimensional position
all these methods , including the computational processes ,are dealt with in later chapters of this book
