What is Plane Table Surveying?
What is Plane Table Surveying?
Plane Table Surveying is a fast and efficient method of surveying which allows for the simultaneous plotting of plans and field observations. This method involves the use of a plane table and alidade to record the geometrical conditions of a particular site on a map sheet, followed by arrangement of topographic details on the map.
Advantages of Plane Table Surveying
Plane Table Surveying has a number of advantages which make it a preferred method of surveying. It is relatively quick and efficient, allows for simultaneous plotting of plans and field observations, and produces precise results. Additionally, its use of the plane table and alidade allows for accurate recording of the site’s conditions, making it an excellent choice for surveying.
Equipment Used in Plane Table Survey
Equipment Needed for Plane Table Survey
Conducting a plane table survey requires several pieces of equipment. The most important of these are a plane table, an alidade for sighting (which may be telescopic or simple), a plumb bob and plumb fork, a compass, a spirit level, a chain, ranging rods, a tripod, drawing sheets and drawing tools, and paper clips or screws.
Plane Table
The plane table is a flat board mounted on a tripod, used to record observations and measurements taken in the field. It is usually equipped with a levelling device and a rotating alidade.
Alidade for Sighting
An alidade is a sighting device used with a plane table to measure angles. It can be a simple or telescopic alidade and is used to measure angles and distances between points on the ground.
Plumb Bob and Plumb Fork
A plumb bob and plumb fork are used to determine the height of points in a survey. The plumb bob is a weight suspended from a string, while the plumb fork is a metal fork with two prongs that can be used to measure angles.
Compass
A compass is used to determine the direction of a line or object in relation to the plane table.
Spirit Level
A spirit level is used to check if the plane table is level when taking measurements. It is a device that consists of a glass tube filled with liquid and a bubble that indicates if the surface is level or not.
Chain
A chain is a measuring device used to measure distances between points in a survey. It is usually made of metal and is marked with intervals to indicate the distance between points.
Ranging Rods
Ranging rods are used to measure distances from the plane table to points on the ground. They are usually made of metal or wood and are marked with intervals to indicate the distance between points.
Tripod
A tripod is used to support the plane table when taking measurements. It is usually made of metal or wood and can be adjusted to different heights.
Drawing Sheet and Drawing Tools
Drawing sheets and drawing tools are used to record observations and measurements taken in the field. They can include pencils, pens, rulers, erasers, and other drawing tools.
Paper Clips or Screws
Paper clips or screws are used to attach the drawing sheet to the plane table. This helps to ensure that the measurements taken are accurately recorded.
Plane table survey equipment is arranged in 4 steps as follows
Fixing of Plane Table
Step 1: Attaching the Plane Table to the Tripod Stand
Attach the plane table securely to the tripod stand and make sure it is stable. To do this, use the screws or clamps that come with the plane table. Make sure the plane table is level and secure before proceeding.
Step 2: Arranging the Drawing Sheet
Once the plane table is securely attached to the tripod stand, it’s time to arrange the drawing sheet. Position the drawing sheet on the plane table and use paper clips or thumb screws to keep the sheet in place. Make sure that the drawing sheet is in the same position from the beginning to the end of the project.
Leveling of Plane Table
Leveling a Table with a Spirit Level
It is important to ensure that a table is level when setting it up. Using a spirit level is the best way to ensure this. A spirit level is an instrument that helps determine if a surface is perfectly level. To use a spirit level, place it on the table and adjust the surface until the bubble in the center of the instrument is centered between the two indicators.
Eye Estimation for Small Works
For smaller works, eye estimation may be sufficient to ensure the table is level. This involves standing back and looking at the table to see if it appears to be level. However, it is best to use a spirit level for accuracy.
Centering of Plane Table
Centering a Table with Plumbing Fork
A plumbing fork is a tool used to help accurately center a table on a ground point. By using a plumbing fork, the point plotted on the table can be precisely aligned with the ground point. This allows for precise measurements and alignment when setting up a table. The plumbing fork is especially useful when setting up a table in an area with uneven terrain or when a precise alignment is required.
Orientation of Plane Table
Orientation In Instrument Surveying
When performing instrument surveys, it is essential to orient multiple instruments. This is done by using a compass or back sighting to rotate the plane table so that the plotted lines in the drawing sheet are parallel to corresponding lines on the ground.
Benefits Of Orientation
Orientation of multiple instruments ensures accuracy in surveying. This is because the instruments will all be pointing in the same direction, ensuring that measurements taken are accurate. Additionally, it allows for easier navigation of the area being surveyed, as the instruments are all pointing in the same direction.
Techniques For Orientation
Compass and back sighting are two techniques used for orientation of instruments in instrument surveying. With compass orientation, a compass is used to rotate the plane table so that the plotted lines in the drawing sheet are parallel to corresponding lines on the ground. With back sighting, a known point is used to orient the instruments. By sighting along the instrument’s line of sight and aligning it with the point, the instrument can be oriented.
Methods of Plane Table Surveying
Radiation Method of Plane Table Surveying
The radiation method of plane table surveying is a method of surveying in which the positions of various points are determined from a known point. It requires a plane table, an alidade, and a telescope. The process involves rotating the plane table and alidade at the known point, sighting the required points one by one, and determining their relative positions by measuring the angles between them.
Intersection Method of Plane Table Surveying
The intersection method of plane table surveying is a method of surveying in which the position of a point is determined by the intersection of two or more lines. It requires a plane table, an alidade, and a telescope. The process involves setting up the plane table and alidade at the point to be surveyed, sighting the required points one by one, and determining their relative positions by measuring the angles between them.
Traversing Method of Plane Table Surveying
The traversing method of plane table surveying is a method of surveying in which the position of a point is determined by a series of connected lines. It requires a plane table, an alidade, and a telescope. The process involves setting up the plane table and alidade at the point to be surveyed, sighting the required points one by one, and determining their relative positions by measuring the angles between them.
Resection Method of Plane Table Surveying
The resection method of plane table surveying is a method of surveying in which the position of a point is determined by measuring the angles between the point and two or more known points. It requires a plane table, an alidade, and a telescope. The process involves setting up the plane table and alidade at the point to be surveyed, sighting the required points one by one, and determining their relative positions by measuring the angles between them.
Radiation
- Introduction to Plane Table Surveying
Plane Table Surveying is a surveying technique used for mapping an area. It involves locating points using an alidade, a sighting device, and plotting them on a drawing sheet. In this method, a plane table is set up at a single point, referred to as Point O, and the whole surveying process is carried out from this point.
- Locate and Plot Points Using Alidade
The alidade is used to sight the points A,B,C,D and E from Point O. These points are then marked on the drawing sheet as a,b,c,d and e respectively. This process helps to accurately map the area and collect the necessary data required for the survey.
Intersection
Steps to Locate a Point Using Two Rays
Step 1: Establish Two Known Stations
In order to locate a point using two rays, the first step is to establish two known stations, labeled P and Q.
Step 2: Plotting the Lines From Station P
Once the two known stations have been established, the next step is to place the equipment on Station P and plot the lines by sighting the stations A, B and Q.
Step 3: Plotting the Lines From Station Q
After plotting the lines from Station P, the equipment should then be shifted to Station Q and the lines should be plotted again by sighting stations A, B and P.
Step 4: Intersection of A and B Rays
The final step is to identify the intersection of the A and B rays, which will be the required location of the point of intersection.
Traversing
What is Traversing?
Traversing is a method used in surveying which involves connecting a series of straight lines. It is done by locating the plane table at one point and then sighting towards the next point. The distance between the two points is then measured and plotted to scale on the drawing sheet. This process is then repeated until the last point is reached, with periodic checks made at certain points. Finally, the traverse lines are plotted on the drawing sheet.
How is Traversing Conducted?
Traversing begins by positioning the plane table at one point (referred to as point A). Sighting towards the next point (point B), the distance AB is measured. The plane table is then shifted to point B and the distance BA is measured. The average of these two distances is then plotted to scale on the drawing sheet. The process is repeated with each successive point, with periodic checks being made. Once the last point is reached, the traverse lines are plotted on the drawing sheet.
Resection
Resection: A Method of Plane Table Surveying
Resection is a method of plane table surveying in which the location of the plane table is unknown and it is determined by sighting it to known points or plotted points. It is also called the method of orientation and it can be conducted by two field conditions.
Resection: The Three-Point Problem
The three-point problem involves orienting the plane table by sighting it to three known points. This method is used when the location of the plane table is unknown and the coordinates of the three known points are known.
Resection: The Two-Point Problem
The two-point problem involves orienting the plane table by sighting it to two known points. This method is used when the coordinates of two known points are known and the location of the plane table is unknown. The two-point problem is less accurate than the three-point problem.
The Three-Point Problem
Tracing Method for Locating Equipment
Tracing is a method of locating equipment by sighting the three known points and tracing their positions on the field. This can be done by using a plane table, which is set up at a position from which all three points are visible. The plane table is used to sight the three points and trace their positions on the field, which helps in determining the location of the equipment.
Lehmann Method for Locating Equipment
The Lehmann Method is a method of locating equipment using the three known points by plotting their positions on a graph. This method involves plotting the three points on a graph and then connecting the points with straight lines. These lines are then used to determine the position of the equipment in the field.
Analytical Methods for Locating Equipment
Analytical methods involve using mathematical equations and formulas to locate equipment. This method involves determining the coordinates of the three known points and then using a mathematical equation to calculate the coordinates of the equipment.
Graphical Method for Locating Equipment
The graphical method is a method for locating equipment using the three known points by plotting their positions on a graph. This method involves plotting the three points on a graph and then connecting the points with lines. The lines are then used to determine the position of the equipment in the field.
Tracing Method in Plane Table Surveying
Step 1: Orienting the Plane Table
The first step in the tracing method is to orient the plane table. This is done by placing the table at a point from which three points are visible. The table is then oriented with respect to the plotted lines of the three points.
Step 2: Placing the Tracing Paper
The second step is to place the tracing paper on the drawing sheet. Sight the three points again and plot the radiating lines.
Step 3: Moving the Tracing Paper
The third and final step is to move the tracing paper above the drawing sheet until the three radiating lines pass through the corresponding points previously plotted on the map. Once this is done, the position of the plane table can then be marked.
Lehmann Method
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What is Plane Table Method?
Plane Table Method is a surveying technique used to measure and map the objects in the field. In this method, a plane table is located at a point P and the station A, B and C are sighted. The rays formed from these stations create a triangle of error.
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Reducing Error with Plane Table Method
To reduce the error, another point P1 is chosen and the point A is sighted from P1, similarly to B and C. This creates another triangle of error. This process is repeated until the error is reduced to zero.
Analytical Methods
Analytical Methods for Three-Point Problem Condition
The three-point problem condition is a method of determining the position of unknown points based on the values of angles and lengths. This technique involves taking measurements from three points, usually designated as stations P, A, B and C, and using analytical formulae to calculate the position of a point.
Calculating Position Using Three-Point Problem Condition
The three-point problem condition allows for the calculation of a position by taking measurements from three points. By taking the angles and lengths of the sightlines between the points, the analytical formulae can be used to determine the position of the unknown point.
Advantages of Three-Point Problem Condition
Using the three-point problem condition has many advantages. It is a fast and accurate method of calculating a position. The analytical formulae used are also straightforward and easy to use. As a result, this method is often used in surveying, navigation and other applications.
Graphical Method
METHODS OF DETERMINING ANGLES AND LENGTHS IN PLANE TABLE SURVEYING
There are two main methods used to determine angles and lengths in Plane Table Surveying: the graphical method and the trigonometric method.
TRIGONOMETRIC METHOD
In the trigonometric method, angles and lengths are determined by measuring the angles and distances between points with the help of a theodolite and the principles of trigonometry. Once the angles and lengths are measured, they can be used to calculate the positions of various points on the plane table.
GRAPHICAL METHOD
The graphical method involves using a graph to represent the angles and lengths between points, and then determining the location of the plane table. Angles and lengths are measured and recorded on the graph, and then the location of the plane table can be determined.
The Two-Point Problem
Step 1: Sighting Point A from Point B
Fig. A and B are the two points corresponding to the points a and b. In order to solve the two-point problem, the plane table is located at Point B and oriented by sighting Point A. The sight C from Point B is plotted on the plane table sheet, forming a line bx.
Step 2: Backsighting Point B from Point C
The plane table is then shifted to Point C, and oriented by backsighting Point B along the line bx. The alidade is placed over Point a and sighted to Point A. The line Aa intersects the line bx at a point which is located as Point c at Station C.
Case 2: Occupying Controlling Stations with Auxiliary Point
Step 1: Locate Plane Table at Auxiliary Point
The plane table is located at the auxiliary point D, which is closer to the controlling station C. The line AB is then parallel to AB to ensure that the plane table is properly situated.
Step 2: Sight from Point A & B
The plane table is then sighted towards station A and B, corresponding to the points a and b. The ray drawn are intersected at some point, which is marked as d.
Step 3: Sight C with Alidade
Using the alidade, the plane table is sighted towards C and the distance Dc is marked as c1. The plane table is then shifted to C and backsight to D with reference to c1.
Step 4: Intersection of Rays
The plane table is then sighted towards A corresponding to a. The ray drawn is intersects the previously drawn ray from D in c2. Sight B, and draw a ray which intersects db and marked the intersection as b1.
Step 5: Orient Table
The table is oriented until ab comes in line with P. From P sight and draw rays Aa and Ba. The intersection of these two rays will give the Location of Point C.
