Plane Table Survey MCQ Quiz - Objective Question with Answer for Plane Table Survey - Download Free PDF

Explanation:

Levelling – First

• The plane table must first be levelled using a spirit level so that all angles and directions can be plotted correctly.

• Levelling ensures the drawing sheet lies in a horizontal plane, which is essential for accurate measurement.

• It is the first and foundational step before proceeding with any plotting.

Centering – Second

• After levelling, the table is centered over the station point using a plumb bob or plumbing fork.

• This ensures that the plotted station point on the drawing sheet lies exactly over the corresponding ground station.

• Proper centering avoids positional errors in the fieldwork and plotting.

Orientation – Third

• Once levelled and centered, the table is oriented using a backsight or compass, aligning it with the previous station or magnetic north.

• Orientation ensures that the direction of the lines drawn corresponds correctly to ground directions.

• Without correct orientation, angular measurements will be inconsistent.

Additional Information

• Plane table survey is a graphical method of surveying where field observations and plotting are done simultaneously on a drawing sheet.

• It operates on the principle of intersection and radiation, allowing direct plotting of angles and distances from a fixed station.

• It eliminates the need for field notes and is ideal for small-scale, moderately accurate surveys.

• The main instruments include a plane table, alidade, spirit level, plumb bob, tripod, and drawing accessories.

• The alidade is used for sighting and drawing rays, while the plumb bob helps in centering the table.

• A spirit level ensures proper levelling, and the tripod provides stability during observations.

Explanation:

Methods of the plane table:

1. Radiation:

• In this method, the instrument is setup at a station, and rays are drawn to various stations which are to be plotted.
• This method is suitable only when the area to be surveyed is small and all the required stations to be plotted are clearly visible and accessible from the instrument station.

2. Traversing:

• This method is similar to compass or theodolite traversing. The table is set at each of the stations in succession.
• This method is most suited when a narrow strip of the terrain is to be surveyed, e.g. survey of roads, railways, etc.

3. Intersection:

• This method is suited when the stations are not visible or the distance between stations is too large. Or in other words, this method is suitable for locating inaccessible points. 
• In this method, two stations are selected such that all the other stations to be plotted are visible from these.
• Sometimes this method is also called graphical triangulation.

4. Resection:

• This method of orientation is employed when the plane table occupies a position not yet plotted on the drawing sheet.
• Resection can be defined as the process of locating the instrument station occupied by the plane table by drawing rays from the stations whose positions are already plotted on the drawing sheet. 
• This method is employed when the surveyor feels that some important details can be plotted easily by choosing any station other than the triangulation stations.

Hence both statements are correct.

Additional Information

Plane Table surveying:

• The plane table is an instrument used for surveying by a graphical method in which the fieldwork and plotting are done simultaneously.
• The main feature of plane tabling is that the topographic features to be mapped are in full view. Hence no chance of missing any important detail.
• It is suitable for small and medium scale mapping, where great accuracy is not required.
• It is also used for plotting the topographical maps in the field.
• Before commencing a plane table surveying, the instrument stations are fixed to cover the entire area.
• This graphical method of producing topographic maps is known as cartographic surveying.
• The principle used in plane table surveying is that an unknown point of interest can be established by measuring its direction from known points.

Concept:

Plane table survey:

A plane table surveying is a graphical method of surveying. In this method of surveying, field observation and plotting are done simultaneously helping the surveyor to compare the plotted details with actual features of the ground.

Advantages of Plane Table Survey:

• It is suitable for the location of details as well as contouring for large-scale maps directly in the field.
• As surveying and plotting are done simultaneously in the field, chances of getting omission of any detail get less.
• The plotting details can immediately get compared with the actual objects present in the field. Thus errors, as well as the accuracy of the plot, can be ascertained as the work progresses in the field.
• The plane table survey is generally more rapid and less costly than most other types of survey.

​
Disadvantages of Plane Table Survey:

• The plane table survey is not possible in unfavorable climates such as rain, fog, etc.
• This method of survey is not very accurate and thus unsuitable for large scale or precise work.
• As no field book is maintained, plotting at different scale require full exercise.
• The quality of the final map depends largely on the drafting capability of the surveyor.

Important Points

The setting of Instruments:

• Fixing
• Leveling
• Centering

Different methods for plane table survey:

• Radiation
• Intersection
• Traversing 
• Resection

Explanation:

Plumb bob and plumb fork: 

• A plumbing fork is a hairpin-shaped brass frame made of arms of equal length.
• One is horizontal (upper arm) has a pointed end and is kept over the drawing sheet touching the plotted position of the instrument station while the other is inclined at a certain angle(lower arm) has a hook from which plumb bob is suspended as shown in the figure.

∴ Hence accurate centering of the plane table is done by using a plumbing fork.

Additional Information

Alidade: 

• It is an instrument used in plane table surveys.
• It is a wooden or brass ruler of about 50-60 cm in length. It is also known as the sight rule.
• Two vanes, the “object vane” and the “sight vane” are hinged at their two ends.

Spirit level (Bubble tube): 

• It is an instrument used in leveling.
• The glass tube containing the liquid and bubbles at a spirit level. In leveling, it is used to check the accuracy of the horizontal surface.

Important Points

The Basic surveying instruments required for plane table surveying are:

1. Plane table
2. Alidade for sighting (telescopic or simple)
3. Plumb bob and plumb fork
4. Compass
5. Spirit level
6. Chain
7. Ranging rods
8. Tripod
9. Drawing sheet and drawing tools

Explanation:

Three points problem of Resection:

(i) It is the process of determining the location of the station that is being occupied by the instrument.

(ii) This method is employed in case the surveyor wants to set up a table at a particular station (say P) towards which no rays had been drawn when the plane table occupied other stations.

(iii) The three point problem can be used if three well defined points A, B and C whose positions a, b and c has already been plotted on the plan/map and which are visible from the plane table station P.

(iv) The following methods are used for the solution of three point problem:

• Trial and error method
• Mechanical method
• Graphical method
• Analytical method
• Geometrical construction method

Explanation:

Plane table surveying is the graphical method of surveying in which field observation and plotting are done simultaneously helping the surveyor to compare the plotted details with actual features of the ground. Method of plane table surveying are,

• Radiation is the method of locating the point by drawing radial lines from the plane table station to that point.
• Intersection is a method of locating a point by the intersection of two rays from two different station.
• Resection is the method of locating the station occupied by the plane table when the position of that station had not been previously plotted from other station.
• Traversing is that type of survey in which a number of connected survey lines form the framework.

Radiation and Intersection are the method to locate the point and Resection is the method to locate the table and Traversing is used in both.

Concept:

Plane table surveying is the graphical method of survey in which the field observations and plotting are done simultaneously.

Plane table surveying is based on the principle that lines drawn during plotting always lie parallel to the corresponding lines actually present on the ground i.e the principle of plane table surveying is parallelism.

Advantages:

1. The observations and plotting are done simultaneously
2. The errors and mistakes in plotting can be checked by drawing check lines
3. Irregular objects can be plotted accurately
4. No great skills are required
5. It is less costly than a theodolite surveying
6. It is advantageous in magnetic areas

Disadvantages:

1. Not suitable for work in a wet climate and in a densely wooded country
2. Difficult to replot the map to a different scale
3. It does not give highly accurate results

Concept:

The errors in plane table surveying are of three types :

1. Instrumental errors: These are:

• Sight vane and object vane of alidade is not perpendicular
• The edge of the alidade is not straight or curved.
• Loose fittings of the tripod and plane table.
• The top surface of the plane table is not flat.
• Faulty spirit level

2. Errors in plotting: These are:

• Use of poor-quality drawing papers.
• Expansion or contraction of drawing paper against temperature changes. 
• The wrong scale of the drawing.
• Use of very thick pencil.

3. Errors due to manipulation and sighting (personal errors or man-made errors):

• Improper clamping of a tripod.
• The drawing sheet of the plane table is not firmly fixed.
• Centering error - the plane table is not exactly over the ground point.
• Improper orientation of plane table.
• Improper sighting through vanes causes errors in direction of the object.

Explanation:

Two-point problems and three-point problems are methods of orientation & resection.

Resection is a method of plane table surveying in which the location of a plane table is unknown. The location of a plane table is determined by looking at it to known points. 

orientation is the operation of turning the table so that all the lines on the paper are parallel to the corresponding lines on the ground.

Location can be determined through:

1. Two points problems:

• Location of the position on the plan, of the station occupied by the plane table by means of observations to two well-defined points whose positions have been previously plotted on the plan.

2. Three points problems:

• Location of the position on the plan, of the station occupied by the plane table by means of observations to three well-defined points whose positions have been previously plotted on the plan.
• Requires less time, labor and more accurate and simpler.

Important Points

1. For plane table surveying, Levelling is performed first, followed by centering and then orientation.

2. For dumpy level, theodolite, and other instruments, centering is done first.

Explanation:

Resection is defined as the process of locating the instrument station occupied by the plane table by drawing rays from the stations whose positions have already been plotted on the drawing sheet. In the three-point problem method, three well-defined points, having locations already being plotted on the drawing are involved. These are used to find and subsequently plot the location of the plane table station.

There are several methods for the solution of the three-point problem:

1. Trial and Error method (Lehman’s method)
2. Mechanical method (Tracing paper method)
3. Graphical method (Bessel’s method)
4. Analytical method
5. geometrical construction method

Of these, the trial and error method is easy, quick and accurate.

Explanation:

Two-point problems and Three-point problems are methods of orientation & resection.

Resection is a method of plane table surveying in which the location of a plane table is unknown. The location of a plane table is determined by looking at it to known points. 

orientation is the operation of turning the table so that all the lines on the paper are parallel to the corresponding lines on the ground.

Location can be determined through:

1. Two points problems:

• Location of the position on the plan, of the station occupied by the plane table by means of observations to two well-defined points whose positions have been previously plotted on the plan.

2. Three points problems:

• Location of the position on the plan, of the station occupied by the plane table by means of observations to three well-defined points whose positions have been previously plotted on the plan.
• Requires less time, labor and is more accurate and simpler.

Three-Point Problem can be solved by:

i) Tracing Paper method

ii) Bessel's Graphical method

iii) Lehman's method

Explanation:

Orientation of Plane table: 

•  Orientation in plane table surveying is the process of putting the plane table into some fixed direction so that line representing a certain direction on the plan is parallel to that direction on the ground.

• This is an essential condition to be fulfilled when more than one instrument station is to be used. 

Methods of Orientation of Plane table:

1. Orientation by trough compass       2. Orientation by mean of back sighting

1. Orientation by trough compass: 

• Orientation by trough compass is less accurate and used for approximate orientation of plane table prior to the final adjustment.
• The plane table can be oriented by compass under the following conditions:

1. ​When speed is more important than accuracy,
2. When there is no second point available for orientation,
3. When the traverse is so long that accumulated errors in carrying the azimuth forward might be greater than the orientation of the compass,

4. For approximate orientation prior to final adjustment.

2. Orientation by mean of back sighting:

• Orientation in plane table surveying can be done precisely by sighting the points already plotted on the sheet. 
• The plane table can be oriented by mean of back sighting the following conditions:

1. When it is possible to set the plane table on the point already plotted on the sheet by way of observation from the previous section.

2. When it is not possible to set the plane table on the point.

Explanation:

Two-point problems and Three-point problems are methods of orientation & resection.

Resection is a method of plane table surveying in which the location of a plane table is unknown. The location of a plane table is determined by looking at known points.

Orientation is the operation of turning the table so that all the lines on the paper are parallel to the corresponding lines on the ground.

Two points problems:

• Knowing the location of the plane table for this auxiliary station is required.
• In a two-point problem, the position of the plane table is determined with two known points. 

Three points problems:

• Location of the position on the plan, of the station occupied by the plane table by means of observations to three well-defined points whose positions have been previously plotted on the plan.
• Requires less time, and labor and is more accurate and simpler.
• Three-Point Problem can be solved by:
  • Tracing Paper method
  • Bessel's Graphical method
  • Lehman's method
  • Mechanical's Method

Concept:

Plane-table survey:

A plane table surveying is a graphical method of surveying. In this method of surveying, field observation and plotting are done simultaneously helping the surveyor to compare the plotted details with actual features of the ground.

Advantages of Plane Table Survey:

• It is suitable for the location of details as well as contouring for small-scale maps directly in the field.
• As surveying and plotting are done simultaneously in the field, chances of getting omission of any detail get less.
• The plotting details can immediately get compared with the actual objects present in the field. Thus errors, as well as the accuracy of the plot, can be ascertained as the work progresses in the field.
• It is less costly than a theodolite surveying
• It is advantageous in magnetic areas

​
Disadvantages of Plane Table Survey:

• The Plane Table is essentially a tropical instruments. It is not suitable to work in wet climate.
• This method of survey is not very accurate and thus unsuitable for large-scale or precise work.
• As no field book is maintained, plotting at different scale require full exercise.
• The quality of the final map depends largely on the drafting capability of the surveyor.

Important Points

The setting of Instruments:

• Fixing
• Leveling
• Centering

Different methods for plane table survey:

• Radiation
• Intersection
• Traversing 
• Resection

Explanation:

Resection and orientation method: 

It 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 as follows:

1. Three-point problem
2. Two-point problem

So, two-point and three-point problems are the methods of resection and orientation.