SURVEYING GLOSSARY
Akheel Ansari
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Monday, 30 April 2012
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accuracy : degree of conformity with a standard. Accuracy relates to the quality of a result, and is distinguished from precision, which relates to the quality of the operation by which the result is obtained. see Accuracy and Precision for further information. easement : areas of land owned by the property owner, but in which other parties, such as utility companies, may have limited rights granted for a specific purpose. encroachment : a structure or part of a structure that occupies the property of another. encumbrance : an interest or partial right in real property which diminished the value of ownership, but does not prevent the transfer of ownership. Mortgages, taxes and judgments are encumbrances known as liens. Restrictions, easements, and reservations are also encumbrances, although not liens. error : the difference between a measured value and the true value. Error in measurement is inherent, but is separate and distinct from a blunder (a mistake). exception : from a title insurance policy, portions of the land containing encumbrances and in which free and clear title is subject to certain conditions. from a legal description, portions of land which are included in the description of a larger parcel of land but then excluded from it by a subsequent legal description. improvement : usually some sort of manmade structure, although perhaps not always a literal "improvement". legal description : a method of describing a particular parcel of land in such a way that it uniquely describes the particular parcel and no other. A legal description may be a simple reference to a lot as shown on a subdivision plat, or be described by metes and bounds. To be adequate, it should be sufficient to locate the property without oral testimony. measurement : an estimated value that is, by its nature, subject to error. A person can count (an absolute value) one hundred beans and get the same quantity as someone else counting one hundred beans. However, if two people each measure (an estimated value) a cup of beans , it is likely that they will have a different quantity of beans. Two surveyors measuring the same distance may obtain different values. Both of the values should be similar, but they will only approach the true theoretical value through repetition and statistical analysis. monument : an object placed to mark the physical location of a position. A property corner monument is often a length of iron rod driven vertically into the ground so that the top is at or below natural grade. A cap identifying the registration number of the surveyor responsible for placing the monument may be placed atop the monument. offset : in boundary: a point located at the extension of a line and marking the direction of the line. An offset monument may be placed on the extension of a line because the offset position can provide a more durable monument. A common practice is to place offset monuments in a sidewalk or curbhead, as these monuments are less likely to be disturbed than a monument marking the actual position. in construction: a short distance usually measured at a right angle to a line, to preserve the position of the line when it is anticipated that points marking the line itself would be disturbed. precision : the degree of refinement in the performance of an operation, or the degree of perfection in the instruments and methods used when making measurements. An indication of the uniformity or reproducibility of a result. Precision relates to the quality of an operation by which a result is obtained, and is distinguished from accuracy, which relates to the quality of the result. see Accuracy and Precision for further explanation. right-of-way : a parcel of land granted by deed or easement for construction and maintenance according to a designated use. This may include highways, streets, canals, ditches, or other uses. subdivision plat : a legal instrument intended to take a large parcel of land and divide it into smaller parcels of land. A subdivision plat may also create public rights-of-way or easements, and is usually filed with the public real estate records of the county. surveying : a blend of several disciplines, from mathematician and law scholar, to expert measurer and translator. By interpreting the legal description and applying the science of measurement, the surveyor translates a legal description or construction plans into tangible positions on the ground. These positions then become the basis for construction or for the establishment of a particular location, possibly to show lines of ownership or to document change over time. title commitment : a commitment to provide title insurance to a parcel of land. The surveyor is interested in the legal description and the exceptions. tolerance : a mathematical term indicating the allowable variation from a standard or from specified conditions. It is an indication of the accuracy and the precision of a measurement. XYZ coordinates : a grouping of three numbers which designate the position of a point in relation to a common reference frame. In common usage, the X and Y coordinate fix the horizontal position of the point, and Z refers to the elevation | ||
STANDARD SURVEYING ABBREVIATIONS | ||
You might find the following corner descriptions on a plat drawing. · FD - Found · IPF - Iron pipe found · IRF - Iron rod found · L.O.D. - Limit of Disturbance. The area to be cleared, graded, etc. · PK - Point Known · PK nail - A surveyor's nail that marks a survey point. See also hub and tack. · SR - Steel rebar · SRS - Steel rod set (rebar or other steel) | ||
SURVEYING WATER TERMS | ||
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TREES | ||
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BASIC'S OF SURVEYING
TYPES OF SURVEY & SURVEYING TECHNIQUES |
ELEMENTARY DEFINITION OF SURVEYING (as paraphrased in most texts):
The art, science, and technology of detecting the relative position of points at, above, or below the surface of the earth; or establishing such points.
BROADER DEFINITION (according to its true nature and scope)
Surveying Measurement:
The art, science, and technology of gathering and analyzing measurement data related to the land and other land-related surfaces and spaces, to include designing and devising the measurement specifications and standards to accomplish these measurements with the desired precision and accuracy and error control and adjustment, including the use of all instrumentation applicable to such measurements, said measurements typically being, but not limited to distances, heights, angles, directions, positions, areas, volumes, and other measurements associated with these quantities.
Professional Surveying:
The application of knowledge of the science of surveying measurement, the legal principles of boundary location, the laws related to boundaries and land use, the applicable mathematical and computational theories and principles, the natural and other forces which affect positional accuracy, the land planning and development concepts pertinent to subdivision of land and property surveys, land record and land tenure concepts, geodetic and other earth-related sciences to the analysis, design, and execution of surveying and mapping projects and the design of land mapping and information systems.
LOGICAL SCOPE OF PROFESSIONAL SURVEYING
1. Original Surveys for Establishing Property Boundaries
2. Retracement of Property Boundaries
3. Field Surveys for Topographic and other Maps
4. Photograrnmetric Surveys for Topographic and other Maps
5. Construction of Maps and other Graphics for Design and Planning
6. Layout and Staking to Guide Construction
7. Measuring and Plotting the Position of Constructed Works
8. Geodetic and other Precise Control Surveys
9. Surveys for Mining and other Subsurface Operations
10. Hydrographic and Underwater Surveys
11. Making Surveys and Maps for Land Information Systems
12. Design of Measurement Specifications for Various Surveys
13. Development of Measurement Standards for Various Surveys
14. Application, Use, and Adjustment of Measurement Instruments
15. Development of Relative Geometric Positional and other Accuracy Needs for Land Information Systems
16. Assisting Engineers, Lawyers, Planners, the Public, and Government Officials with the Solution of Problems Where Surveying Expertise is Needed
THE VALUE OF BEING A SURVEYOR:
Full understanding of the inexactness, uncertainty, and variable nature of measurement leads to humility since it teaches that one can never be sure of results. It is this very humility that, more than anything, creates the professional attitude needed to constantly seek new evidence, and consequently a higher probability of approaching the truth or proving something with confidence.
The surveyor is primarily an analyst. As an analyst of both measurement data and boundary location evidence (including geometric and other mathematical relationships) the surveyor is in a position to develop a keen sensitivity to the importance of finding and applying the truth.
A surveyor, when practicing according to the true nature of surveying, is ever seeking the truth, whether in measurement or in boundary location. Consequently, learning and applying the measurement science and the legal and other principles of boundary retracement develops character.
The art and science of surveying is a mirror of life itself.
Called "Geomatics" in Canada and much of Europe, land surveying is known as the world's second-oldest profession. It dates back to ancient Egypt and Babylonia. Surveying is essentially the art and science of measuring and mapping land. While the entire scope of our profession is vast, it all eventually boils down to determining where people's land boundaries are located. Without this service, railroads could not be built, skyscrapers could not be erected, and individuals could not put up fences around their yards, for fear of trespassing on someone else's land. Would you like an interstate highway to be built in your backyard, one you've paid for, maintained, and paid taxes on for years, without your permission? Of course, how would you know it was in your backyard without a surveyor to tell you where your property even was? We also stake out boundaries of roads to be built, monitor skyscrapers to make sure they are being erected vertically, and measure airports so that the runways are perfectly aligned and smooth. So, if you see a guy in the road looking through an instrument on a tripod, that is a surveyor, now you know that he is doing more than taking pictures.Full understanding of the inexactness, uncertainty, and variable nature of measurement leads to humility since it teaches that one can never be sure of results. It is this very humility that, more than anything, creates the professional attitude needed to constantly seek new evidence, and consequently a higher probability of approaching the truth or proving something with confidence.
The surveyor is primarily an analyst. As an analyst of both measurement data and boundary location evidence (including geometric and other mathematical relationships) the surveyor is in a position to develop a keen sensitivity to the importance of finding and applying the truth.
A surveyor, when practicing according to the true nature of surveying, is ever seeking the truth, whether in measurement or in boundary location. Consequently, learning and applying the measurement science and the legal and other principles of boundary retracement develops character.
The art and science of surveying is a mirror of life itself.
What is a surveyor?
A surveyor is more than one of those guys you see out in the road. Surveying is a vital part of the design and construction process. We perform boundary surveys to tell people where their property is, map the topography of land for engineering design, establish elevations of home sites for flood insurance, perform title surveys for real estate transactions, certify that structures are built according to design, lay out buildings, subdivisions and other construction projects so the construction companies can relate the engineering plans to the real world, and build control networks that all land parcels can relate to in a given area. We also map slopes and areas for pay volumes or quantities, map river bottoms for dredging, lay out photo control for aerial photography and photogrammetry, write legal descriptions that are used to describe pieces of property, map and layout corridors for tunnels, roads, airports, pipelines, cellular networks and railroads, and split up properties into new lots, such as subdivisions.
HISTORY OF SURVEYING
TYPES OF SURVEY & SURVEYING TECHNIQUES |
Surveying is the science and art of measuring distances and angles on or near the surface of the earth. It is an orderly process of acquiring data relating to the physical characteristics of the earth and in particular the relative position of points and the magnitude of areas. Evidence of surveying and recorded information exists from as long ago as five thousand years in places such as China, India, Babylon and Egypt.
Ancient Egyptian surveyors were called harpedonapata (rope-stretcher). They used ropes and knots, tied at pre-determined intervals, to measure distances. The 3-4-5 triangle (later formalized by Pythagoras) was discovered to give a right angle easily by using a rope knotted at distances of 3,4 and 5 units (as below) and shaped (stretched) to form a triangle with a knot at each corner (vertex).
An early instrument for leveling is shown below. It was made from three pieces of wood in the form of an isosceles triangle. A plumb bob suspended from the apex of the frame aligned itself with a notch at the midpoint of the base only when the base was level.
Early Egyptian level
The great Pyramids were presumably laid out using knotted ropes, simple levels and water trough levels for the foundations. The Egyptians used these techniques in the field whilst the Greeks (Pythagoras, Archimedes, Eratosthenes) proved the geometric reasoning behind the principles and demonstrated a clear relationship between mathematics and surveying.Archimedes (by 250 B.C.) recorded that the circumference of the earth is 30 myriads of stadia (300 000 stadia). Stadia is an ancient Greek measure of a distance of 202 yards, or approximately 185 metres. Eratosthenes supported this notion and by some complicated reasoning and calculations using the summer solstice, the sun, angles of shadows and the known position of two towns Syene and Alexandria (Syene was known to be 5 000 stadia due south of Alexandria), found the circumference of the earth to be 25 000 miles. It is in fact 24 881 miles - not bad!
For leveling the Greeks used a chorobate. Wooden poles were often used for linear measurements.
Roman level (Chorobate)
Navigation skills were needed for exploration. Lodestone (a naturally magnetized rock - magnetite) was first used to locate magnetic north and in time the magnetic compass developed for navigation on land and water. An Englishman, Thomas Digges, used the word theodolite to describe an instrument, graduated in 360 degrees, used to measure angles in the mid-1500's. By 1590 the plane table, credited as the invention of Jean Praetorius, was in use. It remained in similar form until the early 1900's. A telescope attached to a quadrant for measuring angles permitted the development of the surveying procedures of triangulation in the 1660's. Sextants, which are precision instruments made from brass or aluminum, became very useful for ocean navigation where celestial observations were taken to plot a ship's position. Sextants accurately measure angles between celestial objects such as the stars, moon and sun, and the horizon from which calculations of position can be made. They are a sophisticated refinement of earlier instruments (cross-staff, quadrant, octant to name a few). The sextant remains today as a valuable tool for ocean navigation. The first dumpy levels appeared in the first half of the 1700's combining a telescope with a bubble level. In 1831, in Philadelphia, W. J. Young invented the transit which exhibited marvelous improvements in accuracy of surveying methods. It allowed the telescope to revolve (transit) on its axis. This meant that both forward and backward sightings could be accurately taken and by repeating the process errors were minimized.The military requirements of two world wars provided the motivation for vast improvements in the design of surveying equipment and execution of surveying operations. In the 1950's Electronic Distance Measurement (EDM) largely replaced triangulation methods for distance measurements. Electronic data collection brought many changes to surveying procedures. The transfer of data collected electronically to computer plotting and drawing systems has reduced time and relieved tedious manual drawing work. The scope of surveying has extended beyond land measurement to include environmental concern for such things as water resources, energy requirements, marine exploration, demarcation of boundaries and protection of the environment.
The use of GPS (Global Positioning System) in surveying procedures is the most recent and revolutionary change to impact land measurement. GPS is very accurate, quick and reliable. However, in conversation with practicing surveyors, I discovered that there is trend to keep older mechanical dumpy levels. This is because they can always be relied on, and trusted, when electronic equipment is faulty or fails, to complete the job in hand.
STANDARD SURVEYING UNITS
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STANDARD SURVEYING TERMS | ||
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SURVEYING SLANG | ||
Surveying, like any profession, has its special terms and slang. Some are just humorous, some help distinguish similar sounds (e.g. eleven and seven), and some are just plain strange!
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SURVEYING TECHNIQUES
TYPES OF SURVEY & SURVEYING TECHNIQUES |
TechniquesThe techniques used for surveying and land measurement are dependent upon the type of survey being conducted. In this section there are two choices: Types of SurveyA simple classification is: 1. Land surveys, which fix property lines, calculate land areas and assist with the transfer of real property from one owner to another. 2. Engineering surveys, which collect the data needed to plan and design engineering projects. The information ensures the necessary position and dimension control on the site so that the structure is built in the proper place and as designed. 3. Informational surveys obtain data concerning topography, drainage and man-made features of a large area. This data is portrayed as maps and charts. Another way to make a simple classification is: 1. Geodetic surveys are precise and over large areas require the curvature of the earth to be considered. Distances and angle measurements must be very, very accurate. A wide variety of techniques are used including triangulation, traversing, trilateration, levelling and astronomical direction fixing. 2. Plane surveys, which consider the surface of the earth to be a plane. Curvature is ignored and calculations are performed using the formulas of plane trigonometry and the properties of plane geometry. These may be considered accurate for limited areas. Sub-categories of the major classes provide more insight into the various fields of surveying as follows: · Property surveys determine boundary lines, property corners, rights-of-way provide data necessary for the preparation of land sub-divisions. · Cadastral surveys are executed by the Federal Government in connection with the disposal of vast areas of land known as the public domain. · Route surveys are necessary for the design and construction of various engineering projects such as roads, railways, pipelines, canals and powerlines. · Industrial surveys, or optical metrology, are used in the aircraft and other industries where very accurate dimensional layouts are required. · Topographic surveys are performed to gather data necessary to prepare topographic maps. These are multicolour contour maps portraying the terrain; and rivers; highways, railways, bridges and other man-made features. · Hydrographic surveys map the shorelines of bodies of water; chart the bottom of streams, lakes, harbours and coastal waters; measure the flow of rivers; and assess other factors affecting navigation and water resources. The sounding of depths by radar is involved in this type of survey. · Mine surveys determine the position of underground works such as tunnels and shafts, the position of surface structures and the surface boundaries. · Aerial surveys use photogrammetry to produce a mosaic of matched vertical photographs, oblique views of landscape and topographic maps drawn from the photographs. · Construction surveys fix elevations, horizontal positions and dimensions for construction projects. · Control surveys provide basic horizontal and vertical position data. These are called datum. For most surveying work the vertical position of points in terms of height above a curved reference surface is mean sea level. 3. Traverse 4. Leveling 5. Radiation TriangulationTriangulation consists of a series of connected triangles which adjoin or overlap each other, angles being measured from determined fixed stations. Triangulation reduces the number of measures that need to be taped and for this reason is often a preferred method of survey. A known base-line measurement is required. Three examples of triangulation systems are shown below. A single chain of triangles is a rapid and economical system for covering a narrow strip of land. A chain of quadrilaterals is more accurate with checks being made by various combinations of angles and sides as the survey proceeds. Larger areas use a central point arrangement. A point to note is that all angles should be more than 20°. Angles less than 20° are not considered valid for fixing position. They introduce inaccuracies. This is much the same in navigation where a fix by two bearings requires an angle of intersection of approximately 90°, and for three bearings approximately 60°. Angles less than 30° are not acceptable. TrilaterationTrilateration uses electronic distance measuring equipment to directly measure the lengths of the sides of triangles from which the angles can be calculated. It is a very useful method for rough terrain where positions can be accurately carried forward and is seen as an alternative method to triangulation. TraverseA traverse consists of a series of lines, whose lengths and directions are measured, connecting points whose positions are to be determined. The route of the traverse line can be adjusted for obstacles such as rough or timbered terrain, swampy land, buildings and areas of heavy traffic. A traverse may be either open or closed as shown below. An open traverse begins at a point of known position and ends at a station whose relative position is unknown. This type of traverse is frequently used for preliminary surveys for highways. A closed traverse begins and ends at the same point whose position is known. An example of this type of traverse is a perimeter survey of a tract of land. LevelingLeveling is the operation of determining differences of elevation by measuring vertical distances directly on a graduated rod with the use of a leveling instrument such as a dumpy level, transit or Theodolites. This method is called direct leveling or differential leveling. Indirect leveling can be done using the principle that differences in elevation are proportional to the differences in atmospheric pressure. The difference in elevation between two points can also be determined trigonometrically using vertical angles and horizontal or inclined distances. Differential leveling Benchmarks are very important in leveling. They are permanent objects of known elevation located where there is least likelihood of disturbance. They may be a metal or concrete post set close to the ground, a notch in a tree root or a peg or spike in a tree. RadiationRadiation is a surveying technique often used in conjunction with a plane table. From a fixed position directly above the corresponding location on the ground bearings are taken to various points at the boundary of the survey area. The bearing lines are drawn on the paper on the table. Distances to the points are measured and then converted to the required scale on the survey sheet. Radiation surveying can be performed in a similar way directly on the ground taking bearings and distances from a fixed position and recording them for later work. Similarly plane table surveying may be used with other techniques such as a traverse or triangulation. |
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