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Detail Surveying: Stages, Techniques, and Calculations, Exercises of Cost Accounting

Abasyn University Peshawar (AUP)Cost Accounting

The stages of detail surveying, including specification, reconnaissance, establishment of control, observation of detail, calculations, and plotting. It covers the use of electronic total stations for measurement and computation, the importance of detailed sketching, and procedures for using co-ordinates. The document also includes an example of poor detail sketching and worked examples of calculation processes.

Typology: Exercises

2020/2021

Uploaded on 08/29/2021

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School of Architecture, Design & the Built Environment
Civil Engineering Programmes
8. Detail Surveying
Page 1 of 17
Module Notes 8. Detail Surveying
Stages involved in detail surveying
Specification
Reconnaissance
Establishment of control (horizontal and vertical)
Observation of detail
Calculations
Plotting
Field checking
Specification/Brief (provided by client)
o Location and extents of survey required.
o Scale of survey (dictates degree of detail to be surveyed). Note that this is not necessarily the same
as the scale of any plot/plan required. Plans should not be produced at a scale which is larger than
that of the survey – why not?
o Type of survey control stations or markers to be used.
o How is the survey to be presented to the client – paper plan, electronic 2D file, electronic 3D ground
model? If electronic, what file format, for use in which programme?
o Any special requirements.
Reconnaissance
o Identify on the ground the extents/boundaries of the survey specified.
o Identify any areas of detail likely to be particularly problematic to observe, or any areas of uncertainty
about whether or not detail is required, to be resolved with the client.
o Find and identify any existing control stations to be used, and/or choose locations for new control
stations. Depending on the specification and on the requirements of the job, a control station may be
any one of a number of different types, including a proprietary survey ground marker, a nail in a
wooden peg, a steel bar set in concrete (either a pre-cast block or cast in-situ), a road nail through a
washer hammered into asphalt or between kerb stones, or a Hilti or similar nail fired into a concrete
surface.
New control stations should be placed with the following considerations taken into account:
Intervisibility of adjacent points (which may change seasonally).
Suitability of position with respect to detailing.
Suitability for convenience of instrument setting and observing comfort.
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Civil Engineering Programmes

  1. Detail Surveying

Module Notes 8. Detail Surveying

Stages involved in detail surveying  Specification  Reconnaissance  Establishment of control (horizontal and vertical)  Observation of detail  Calculations  Plotting  Field checking Specification/Brief (provided by client) o Location and extents of survey required. o Scale of survey (dictates degree of detail to be surveyed). Note that this is not necessarily the same as the scale of any plot/plan required. Plans should not be produced at a scale which is larger than that of the survey – why not? o Type of survey control stations or markers to be used. o How is the survey to be presented to the client – paper plan, electronic 2D file, electronic 3D ground model? If electronic, what file format, for use in which programme? o Any special requirements. Reconnaissance o Identify on the ground the extents/boundaries of the survey specified. o Identify any areas of detail likely to be particularly problematic to observe, or any areas of uncertainty about whether or not detail is required, to be resolved with the client. o Find and identify any existing control stations to be used, and/or choose locations for new control stations. Depending on the specification and on the requirements of the job, a control station may be any one of a number of different types, including a proprietary survey ground marker, a nail in a wooden peg, a steel bar set in concrete (either a pre-cast block or cast in-situ), a road nail through a washer hammered into asphalt or between kerb stones, or a Hilti or similar nail fired into a concrete surface. New control stations should be placed with the following considerations taken into account:  Intervisibility of adjacent points (which may change seasonally).  Suitability of position with respect to detailing.  Suitability for convenience of instrument setting and observing comfort.

Civil Engineering Programmes

  1. Detail Surveying  Stability of pegs (avoid siting pegs in boggy or marshy areas) and of nails (avoid placing nails into asphalt which may soften and move in hot sunlight).  Safety of both observer and passers-by. o Locate Ordnance Survey benchmarks (if the levels are to be related to Ordnance Datum) and Ordnance Survey control points (if the co-ordinates are to be tied into the National Grid). Establishment of control o The co-ordinates of control stations may be determined by observation and computation using a number of different techniques, e.g. traversing, intersection, resection, network, all observed using electronic total stations, or by network using GPS/Glonass receivers. The only technique covered on this course is traversing with a total station, which involves primarily the measurement of horizontal and vertical angles and slope distances – see the course notes previously issued entitled ‘Angular Measurement’ and ‘Traversing’, or any of the standard surveying text books, for details. o The level of control stations may be determined by standard levelling, precise levelling or GPS observations depending on the specification and/or the requirements of the job. Levels may be relative to an arbitrary datum or related to some other datum, e.g. Ordnance Survey datum. Detailing Plottable error Before starting to take detail observations, it is necessary to know the scale at which the survey is required, in order to determine the degree of detail to be captured. In conventional surveying, the scale of the final plan to be produced (whether on paper or in computer file form) will have been specified by the client. With knowledge of the required scale, the accuracy requirements of the survey are determined using the principle known as plottable error, or plotting accuracy. Plottable error for both manual and computer drafting is usually taken as ±0.2mm on the paper. A scale stated as 1:n means that 1 unit on the paper represents n units on the ground, e.g. at a scale of 1:1000, 1mm on the paper represents 1000mm (1m) on the ground. Therefore, a plottable of error of ±0.2mm represents 200mm on the ground at a scale of 1:1000 or 10mm at a scale of 1:50. Table 1 shows the relationship between plan scale and plottable error for a range of scales. In other words, for a plot to be produced that shows all features in their correct location and with the correct dimensions to the normal surveying standards of plotting accuracy, the data has to be collected to a higher accuracy than the plottable error. It can be appreciated that for a large scale such as 1:50 or larger, the accuracy requirement is demanding.

Civil Engineering Programmes

  1. Detail Surveying Detail techniques and requirements A number of techniques may be used within any one detail survey, e.g. EDM tacheometry using an electronic total station, direct measurement and angle intersection. The detail required will typically include:  buildings  roads, footpaths and tracks (state surface type)  boundaries (state type of boundary construction, e.g. hedge, brick wall, post and wire fence, and where appropriate state height and width). For hedges define centre-line or trunk-line and extent of canopy.  street furniture (lamp posts, road signs, gullies, etc.)  services (utilities) where evident at the surface (manholes, inspection covers etc.)  trees (state height, spread [diameter of canopy] and girth [circumference measured 1m above ground], also useful to note if they have a tree preservation order [TPO] tag affixed to the trunk)  any other significant features. Some of the dimensional and most of the textual information related to these can be gathered at the sketching stage prior to starting detail observations. Sketching Prior to observing detail with a total station (see next section), it can be very useful to sketch all or parts of the area to be surveyed. The sketches serve several purposes:  they provide the surveyor with a thorough knowledge of the area to be surveyed, and the process of sketching can often bring to light hidden features which might otherwise have gone unnoticed, or areas of complicated detail which need alternative methods of data observation to be considered;  they enable dimensions (of trees, manholes, walls etc.) and textual information (e.g. surface type, wall or fence type) to be collected and noted prior to the detailing, making the latter a quicker, smoother, more cost-effective process without frequent pauses;  they enable the observation number to be clearly recorded against each point of detail as it is observed, which minimises note-taking at the instrument, which can be a slow process when done electronically;  the sketches, plus the background knowledge gained while making them, help the surveyor to resolve any problems which might be encountered during plotting, e.g. observation or calculation errors causing points to plot out of position;  they should allow anyone else to carry-out or complete the plotting should the surveyor be unable to.

Civil Engineering Programmes

  1. Detail Surveying The sketches should be made in pencil, with an eraser to hand; they should be approximately to scale, and should be large-enough scale to allow absolutely clear and unambiguous recording of all the required information. Figures 1 and 2 and the notes below each show examples of bad and good sketching Figure 1. Example of poor detail sketching  Covers large area in insufficient detail.  Detail is cramped and unclear, requiring an enlargement of the bottom left area: enlargement is itself cramped and unclear.  No explanation of what the various lines represent, and no surface materials identified.  Detail point numbers written from a variety of different directions; some points un-numbered.  No dimensions shown.  Insufficient detail points and no direct measurements observed: it is impossible to fully plot this area of detail from the observed data and this sketch.

Civil Engineering Programmes

  1. Detail Surveying Procedure using raw data:  Set-up over a control station, and measure the height of instrument.  Set-up a target on a tripod over another control station and measure the height of target. This will be the Reference Object, or RO. o The control station to be used as RO should be further from the instrument position than the longest detail sight to be taken, i.e. you should not necessarily use the nearest control station as an RO.  Sight the RO target, and set the horizontal circle to the value of the bearing to that station (calculated from the final adjusted control co-ordinates obtained from the control traverse computation). All horizontal circle readings to detail points will now actually be bearings. o If you don’t know the bearing to the RO, set the circle to read zero. If you set it some random number the computations will be much more difficult. o If you forget to record what the circle was set to, the detail observations cannot be processed and you will have to repeat the detail observations.  Take an observation to the RO and confirm that the displayed horizontal distance and height difference agree with those computed from final co-ordinates and levels.  Detailing can now be carried out, recording point number, target height (height of prism on the detail pole, which is also known as a pogo stick), horizontal angle, vertical angle, slope distance and point description. A single observation to the pogo on one face only is sufficient for detailing purposes. o It is wise to take the first observation to an adjacent control station (a different one from the RO) where the distance and height difference are already known. This serves as a check against gross error in reading the instrument and in earlier calculations. Ensure also that some common detail is observed from adjacent tcp’s. o Every 20 to 30 observations, check that the booker and the person at the detail pole recording the points on the sketch are in agreement as to the current point number. It is possible for them to get out of synchronisation, which can lead to ‘spaghetti’ data when plotted. o Always observe and book an RO check every 20 – 30 observations, and ALWAYS as the last observation at a station.  The raw data will now need to be processed to obtain horizontal distance and height difference, and then further processed to compute co-ordinates and reduced level for each point. Examples of data reduction and processing follow below.  Plotting can then take place by co-ordinates.

Civil Engineering Programmes

  1. Detail Surveying Procedure using co-ordinates (in outline – there are many makes and models of total station, all with differing functionality and software, so the procedure here is generalised):  Follow the same procedure as above but, if you wish the instrument to compute and display the co-ordinates of the detail points, and it has that facility, enter the co-ordinates of the instrument control station before sighting the RO. On some instruments you can also enter the co-ordinates of the RO and the instrument will compute the bearing to the RO from the instrument station.  As above, sight the RO target, and set the horizontal circle to the value of the bearing to that station, or, if you have entered instrument and RO co-ordinates, follow the instrument prompts so that the instrument does this automatically.  Take an observation to the RO and confirm that the displayed co-ordinates agree with the final adjusted co-ordinates from the traverse computation. Book also the raw data (horizontal angle, vertical angle and slope distance) to the RO, as this will aid error rectification should problems occur.  Detailing can now be carried out, recording point number, target height (height of prism on the detail pole), co-ordinates, reduced level and point description. Book also the raw data (horizontal angle, vertical angle and slope distance), as this will aid error rectification should problems occur.  As before, always observe and book an RO check every 20 – 30 observations, and ALWAYS as the last observation at a station.  Plotting is now simply by coordinates without the need for any prior computation. In terms of gathering the data, if it is to be recorded electronically, either stored directly on the instrument or though a connected data logger, it is usual to code the data points to allow easier plotting of the data to be subsequently carried out in either a proprietary survey software package or in a basic CAD package. The data is normally observed in ‘ strings ’, that is for example all points along a particular fence line are observed in order and coded as such, e.g. a fence line might be coded as FE 01
  • FE standing for fence and the 0 1 for it being the first fence line such that not all points coded FE are automatically joined together even if they are not on the same fence line; buildings may be coded as BD, walls as WL etc. Each string line should be surveyed along its extent in one go rather than jumping from one string line to another to avoid having to change features codes between each observation, and to also lessen the amount of data editing required in the plotting. Using codes will allow the survey package, if correctly set up, to join the relevant points on the string line together with an appropriate line type allowing the outline survey to be developed directly with minimal user interface. You will often find that instruments have a built in ‘ code library’ that can be used to speed up the process and ensure consistency between users.

Civil Engineering Programmes

  1. Detail Surveying Figure 4. Hard detail by chainage and offset A, B are survey control stations; X is Chainage; O is offset. Distance AB is b. Now tan  =

X

O

and tan =

(b-X )

O

 O = X.tan  = (b-X).tan   X(tan  + tan ) = b.tan   X =   

tan tan

tan

b.

and O =    

b..

tan tan

tan tan

Running measurements to the remaining detail may then be taken from the building corners. Detail calculations Reduction of slope distance to horizontal Figure 5 a shows the relationship between vertical angle and zenith angle, but most surveyors and instrument manufacturers, confusingly, use the terminology shown in Figure 5 b. The text and equations following all use the terminology shown in Figure 5 a. (a) (b) Figure 5. Vertical angle terminology Line of sight Zenith angle Vertical angle (horizontal) Line of sight Vertical angle Reduced vertical angle (horizontal)

Civil Engineering Programmes

  1. Detail Surveying The relationship between slope distance, horizontal distance and vertical difference in height is given by simple trigonometry (Figure 6 ). Figure 6. SD, HD & ΔH HD = SD. cos(VA) = SD. sin(ZA) ΔH = SD. sin(VA) = SD. cos(ZA) Note that if ZA is > 90° (horizontal in face left) or < 270° (horizontal in face right), both VA and ΔH will be negative. Many total stations can be set to display either ZA or VA. In carrying out reductions manually it makes no difference which is used provided the appropriate equations are employed. Plan position To obtain the co-ordinates of any detail point P, the following equations are used:. Ep = Estn + ΔE = Estn + D sin(ß) Np = Nstn + ΔN = Nstn + D cos(ß) , where Estn, Nstn are the co-ordinates of the survey control station (instrument position) D is the horizontal distance from instrument to detail point ß is the bearing from instrument to detail point and Ep, Np are the required co-ordinates of detail point P. The bearing ß from instrument to detail point is given by: ß = (bearing from instrument station to reference object) + (observed horizontal angle) and will either be the horizontal circle reading taken from the total station (if that was set to the correct bearing when sighting to the RO), or the horizontal circle reading plus bearing to the RO (if the circle was set to zero when sighting to the RO). HD Horizontal Vertical VA ZA ΔH SD

Civil Engineering Programmes

  1. Detail Surveying

Civil Engineering Programmes

  1. Detail Surveying Worked example Instrument station A: 500mE, 2000mN, elevation (RL) 10m Bearing to Reference Object B: 90° 00’ 00” Height of instrument: 1.520m Height of target on RO: 1.663m Height of target on pole: 1.520m Observations: SD ZA HA to RO 150.364m 88° 54’ 16” 000° 00’ 00” to detail point P 74.230m 91° 25’ 22” 124° 33’ 21” Calculations: to RO HD = SD. sin(ZA) = 150.364 x sin (88° 54’ 16”) = 150.364 x 0. = 150.337m ΔH = SD. cos(ZA) = 150.364 x cos (88° 54’ 16”) = 150.364 x 0. = +2.875m Easting of RO = Ea + D. sin(ß) = 500.000 + 150.337 x sin(90° 00’ 00”) = 500.000 + 150. = 650.337m Northing of RO = Na + D. cos(ß) = 2000.000 + 150.337 x cos(90° 00’ 00”) = 2000.000 + 0 = 2000.000m Level of RO = RLa + Hi + ΔH - Ht = 10.000 + 1.520 + 2.875 - 1. = 12.732m (RO = 650.337mE, 2000.000mN, 12.732m Ht) – check against given values to point P: HD = SD. sin(ZA) = 74.230 x sin (91° 25’ 22”) = 74.230 x 0. = 74.207m ΔH = SD. cos(ZA) = 74.230 x cos (91° 25’ 22”) = 74.230 x (-0.024830) = - 1.843m Bearing to P = 90° 00’ 00” + 124° 33’ 21” = 214° 33’ 21” Easting of P = Ea + D. sin(ß) = 500.000 + 74.207 x sin(214° 33’ 21”) = 500.000 + 74.207 x (-0.567209) = 500.000 - 42. = 457.909m Northing of P = Na + D. cos(ß)

Civil Engineering Programmes

  1. Detail Surveying

  2. Using the T-square against the edge of the board, you should now be able to draw a line through the intersection of both diagonals and the upper arcs. If the line doesn't pass through both intersections, your construction has not been good enough.

  3. Join the intersections of the upper and lower arcs on both left and right sides of the paper.

  4. You now have a very faint rectangle which is truly rectangular, i.e. opposite sides parallel and corner angles of 90º. This is purely for construction of the framework for the grid – nothing to do with the survey yet. Figure 8. Construction of framework for a grid

  5. By inspection of your detail and/or control station co-ordinates, determine the distance from edge of drawing area (i.e. edge of paper less 10mm border less aesthetic space) to the first N-S grid line, such that the E-W extents of the survey will fit on the paper allowing for border and title block; do similarly for the first E-W grid line. For example, if the point that is furthest east has an Easting of 512.358m, it lies 12.358m from the 500mE grid line. At a scale of 1/100, that would be 123.6mm on the drawing. Working in from the right hand edge of the paper, allowing 10mm for the border and, say, 15mm aesthetic white space, the 500mE grid line would be 148.6mm from the edge of the paper. Measure along the lower line and mark this distance. Measure between this mark and the right vertical line; measure the same distance along the top line and mark, and join the two marks to give the 500mE line running up and down the paper, parallel to your faint construction line. Follow a similar process to fix the position of an EW grid line. In both cases, remember to allow space for the title block. Once the position of one NS and one EW grid lines are marked, then measure from those along the top, bottom, left and right

Edge of paper

Compass centre

Civil Engineering Programmes

  1. Detail Surveying construction lines and mark the remaining grid lines. The interval would typically be every 20m for a 1/200 scale plan, and every 10m or maybe 5m for a 1/100 scale plan.

  2. Detail is then plotted by measuring along the grid lines the required amount for each detail point in turn, and marking a small + at each point. Keep any measuring marks along the grid lines very faint indeed, so that they won't detract from the finished pencil plot. Detail points are then connected with the appropriate lines following the point descriptions and the sketches. All detail should be drawn faintly until it is all complete, and then firmed-in, annotations, levels etc. added, and grid intersections (not full grid lines) drawn in. The addition of grid co-ordinates around the edges of the drawing, North arrow, scale bar and title block with appropriate entries will complete the drawing. Computer plotting The output from the detail point calculations was a list of point numbers each with Easting, Northing, height and description. These need to be converted into a file readable by an appropriate CAD program. The program such as xyz2dxf.exe will convert a file which is a comma-separated variable (.csv) file into a .dxf file which can be read by AutoCAD. The csv file can be created by typing or pasting the required data into Excel, saving it as a CSV (Comma-Delimited) file, and running the xyz2dxf program. The columns of the csv file must be point number, Easting, Northing, Height, Description. The resulting .dxf file can then be opened in AutoCAD to reveal a cross plotted for each point; the points can then be joined in AutoCAD using appropriate line styles, and annotation, border, North arrow, scale bar and title block added as in the manual process. Hybrid plotting If your AutoCAD skills are not advanced enough to do all the on-screen editing to produce a finished drawing, you may use the xyz2dxf.exe program to plot all your detail points in AutoCAD, plot the unedited drawing at the specified scale, and then complete the drawing by manual editing as described above.