Photogrammetric Surveying

 Photogrammetric Surveying

It is the branch of surveying in which maps are prepared from photographs taken from

ground or air stations. Photographs are also being used for interpretation of geology,

classification of soils, crops, etc. 

The art, science, and technology of obtaining reliable information about physical

objects and the environment through process of recording, measuring, and interpreting

photographic images and patterns of recorded radiant electromagnetic energy and

phenomenon.

Originally photogrammetry was considered as the science of analysing only

photographs. 

Advantages and Disadvantages: 

Some advantages of photogrammetry over conventional surveying and mapping methods are: 

 It provides a permanent photographic record of conditions that existed at the time the

aerial photographs were taken. Since this record has metric characteristics, it is not only

a pictorial record but also an accurate measurable record. 

 If information has to be re-surveyed or re-evaluated, it is not necessary to perform

expensive field work. The same photographs can be measured again and new

information can be compiled in a very timely fashion. Missing information, such as

inadequate offsets for cross sections, can be remedied easily. 

 It can provide a large mapped area so alternate line studies can be made with the same

data source can be performed more efficiently and economically then other

conventional methods. 

 It provides a broad view of the project area, identifying both topographic and cultural

features. 

 It can be used in locations that are difficult, unsafe, or impossible to access.

Photogrammetry is an ideal surveying method for toxic areas where field work may

compromise the safety of the surveying crew. 

 An extremely important advantage of photogrammetry is that road surveys can be done

without closing lanes, disturbing traffic or endangering the field crew. Once a road is

photographed, measurement of road features, including elevation data, is done in the

office, not in the field. 

 Intervisibility between points and unnecessary surveys to extend control to a remote

area of a project are not required. The coordinates of every point in the mapping area

can be determined with no extra effort or cost. 

 The aerial photographs can be used to convey or describe information to the public,

State and Federal agencies, and other divisions within the Department of

Transportation. 

Some disadvantages are: 

 Weather conditions (winds, clouds, haze etc.) affect the aerial photography process and

the quality of the images. 

 Seasonal conditions affect the aerial photographs, i.e., snow cover will obliterate the

targets and give a false ground impression. Therefore, there is only a short time

normally November through March, that is ideal for general purpose aerial

photography. A cleared construction site or a highway that is not obstructed by trees, is

less subjected to this restriction. These types of projects can be flown and photographed

during most of the year. 

 Hidden grounds caused by man-made objects, such as an overpass and a roof, cannot

be mapped with photogrammetry. Hidden ground problems can be caused  by tree

canopy, dense vegetation, or by rugged terrain with sharp slopes. The information

hidden from the camera must be mapped with other surveying methods. 

 The accuracy of the mapping contours and cross sections depends on flight height and

the accuracy of the field survey. 

History of Photogrammetry: 

1851: French officer Aime Laussedat develops the first photogrammetrical devices and

methods. He is seen as the initiator of photogrammetry. 

1858: The German architect A. Meydenbauer develops photogrammetrical techniques for

the documentation of buildings and installs the first photogrammetric institute in 1885 

(Royal Prussian Photogrammetric Institute). 

1885: The ancient ruins of Persepolis were the first archaeological object recorded

photogrammetrically. 

1889: The first German manual of photogrammetry was published by C. Koppe. 

1911: The Austrian Th. Scheimpflug finds a way to create rectified photographs. He is

considered as the initiator of aerial photogrammetry, since he was the first succeeding to 

apply the photogrammetrical principles to aerial photographs 

1913: The first congress of the ISP (International Society for Photogrammetry) was held

in Vienna. 

1980: Due to improvements in computer hardware and software, digital photogrammetry

is gaining more and more importance. 

1996: 83 years after its first conference, the ISPRS comes back to Vienna, the town,

where it was founded. 

Classification of Photogrammetry: 

Photogrammetry is divided into different categories according to the types of photographs or

sensing system used or the manner of their use as given below: 

I. On the basis of orientation of camera axis:  

a. Terrestrial or ground photogrammetry 

When the photographs are obtained from the ground station with camera axis horizontal

or nearly horizontal         

b. Aerial photogrammetry

If the photographs are obtained from an airborne vehicle. The photographs are 

called vertical if the camera axis is truly vertical or if the tilt of the camera axis is less

than 3 degree

. If tilt is more than (often given intentionally), the photographs are

called oblique photographs. 

II. On the basis of sensor system used:  

     Following names are popularly used to indicate type of sensor system used:  

 Radargrammetry: Radar sensor  

 X-ray photogrammetry: X-ray sensor  

 Hologrammetry: Holographs  

 Cine photogrammetry: motion pictures  

 Infrared or colour photogrammetry: infrared or colour photographs  

III. On the basis of principle of recreating geometry:  

When single photographs are used with the stereoscopic effect, if any, it is

called Monoscopic Photogrammetry.  

If two overlapping photographs are used to generate three dimensional view to create relief

model, it is called Stereo Photogrammetry. It is the most popular and widely used form of

photogrammetry.  

IV. On the basis of procedure involved for reducing the data from photographs: 

Three types of photogrammetry are possible under this classification:  

a. Instrumental or Analogue photogrammetry: It involves photogrammetric

instruments to carry out tasks.  

b. Semi-analytical or analytical: Analytical photogrammetry solves problems by

establishing mathematical relationship between coordinates on photographic image and

real world objects. Semi-analytical approach is hybrid approach using instrumental as

well analytical principles.  

c. Digital Photogrammetry or softcopy photogrammetry: It uses digital image

processing principle and analytical photogrammetry tools to carry out photogrammetric

operation on digital imagery.  

V. On the basis of platforms on which the sensor is mounted:

If the sensing system is space borne, it is called Space Photogrammetry, Satellite 

Photogrammetry or Extra-terrestrial Photogrammetry. Out of various types of the

photogrammetry, the most commonly used forms are Stereo Photogrammetry

utilizing a pair of vertical aerial photographs (stereo pair) or terrestrial photogrammetry

using a terrestrial stereo pair.   

Application of Photographic Survey: 

Photogrammetry has been used in several areas. The following description give an overview

of various applications areas of photogrammetry  

a. Geology: Structural geology, investigation of water resources, analysis of thermal patterns

on earth's surface, geomorphological studies including investigations of shore features.  

• Stratigraphic studies 

• General geologic applications 

• Study of luminescence phenomenon 

• Recording and analysis of catastrophic events

• Earthquakes, floods, and eruption.  

b. Forestry:  Timber inventories, cover maps, acreage studies 

c. Agriculture: Soil type, soil conservation, crop planting, crop disease, crop-acreage.

d. Design and construction: Data needed for site and route studies specifically for 

alternate schemes for photogrammetry. Used in design and construction of dams,

bridges, transmission lines.  

e. Planning of cities and highways: New highway locations, detailed design of

construction contracts, planning of civic improvements.  

f. Cadastre: Cadastral problems such as determination of land lines for assessment of

taxes. Large scale cadastral maps are prepared for reapportionment of land. 

g. Environmental Studies:

h. Land-use studies.

i. Urban area mapping.

j.  Exploration: To identify and zero down to areas for various exploratory jobs such as 

oil or mineral exploration. 

k. Military intelligence: Reconnaissance for deployment of forces, planning manoeuvres, 

assessing effects of operation, initiating problems related to topography, terrain

conditions or works.  

l. Medicine and surgery: Stereoscopic measurements on human body, X-ray

photogrammetry in location of foreign material in body and location and examinations

of fractures and grooves, biostereometrics.  

m. Mountains and hilly areas can be surveyed easily.

n. Miscellaneous 

Classification of Photographs:    

The following paragraphs give details of classification of photographs used in different

applications     

A. On the basis of the alignment of optical axis  

 Vertical: If optical axis of the camera is held in a vertical or nearly vertical position. 

 Tilted: An unintentional and unavoidable inclination of the optical axis from vertical

produces a tilted photograph.  

 Oblique: Photograph taken with the optical axis intentionally inclined to the vertical.

Following are different types of oblique photographs:  

i.  High oblique: Oblique which contains the apparent horizon of the earth. 

ii. Low oblique: Apparent horizon does not appear.  

iii. Trimetrogon: Combination of a vertical and two oblique photographs in which

the central photo is vertical and side ones are oblique. Mainly used for

reconnaissance. 

iv. Convergent: A pair of low obliques taken in sequence along a flight line in

such a manner that both the photographs cover essentially the same area with

their axes tilted at a fixed inclination from the vertical in opposite directions in

the direction of flight line so that the forward exposure of the first station forms

a stereo-pair with the backward exposure of the next station.  

ASTRONOMICAL SURVEYING

 ASTRONOMICAL SURVEYING

Celestial Sphere. 

The millions of stars that we see in the sky on a clear cloudless night are all at varying distances from us. Since we are concerned with their relative distance rather than their actual distance from the observer. It is exceedingly convenient to picture the stars as distributed over the surface of an imaginary sphericalsky having its center at the position of the observer. This imaginary sphere on which the star appears to lie or to be studded is known as the celestial sphere. The radius of the celestial sphere may be of any value - from a few thousand metres to a few thousand kilometers. Since the stars are very distant from us, the center of the earth may be taken as the center of the celestial sphere.

Zenith, Nadir and Celestial Horizon.

 The Zenith (Z) is the point on the upper portion of the celestial sphere marked by plumb line above the observer. It is thus the point on the celestial sphere immediately above the observer's station. The Nadir (Z') is the point on the lower portion of the celestial sphere marked by the plum line below the observer. It is thus the point on the celestial sphere vertically below the observer's station. Celestial Horizon. (True or Rational horizon or geocentric horizon): It is the great circle traced upon the celestial sphere by that plane which is perpendicular to the Zenith-Nadir line, and which passes through the center of the earth. (Great circle is a section of a sphere when the cutting plane passes through the center of the sphere)

Terrestrial Poles and Equator, Celestial Poles and Equator. 

The terrestrial poles are the two points in which the earth's axis of rotation meets the earth's sphere. The terrestrial equator is the great circle of the earth, the plane of which is at right angles to the axis of rotation. The two poles are equidistant from it. If the earth's axis of rotation is produced indefinitely, it will meet the celestial sphere in two points called the north and south celestial poles (P and P'). The celestial equator is the great circle of the celestial sphere in which it is intersected by the plane of terrestrial equator.

CO-ALTITUDE OR ZENITH DISTANCE (Z) AND AZIMUTH (A).

It is the angular distance of heavenly body from the zenith. It is the complement or the altitude, i.e. z = (90 - θ) degree. The azimuth of a heavenly body is the angle between the observer's meridian and the vertical circle passing through the body

Trigonometric Leveling

 Trigonometric Leveling

Definition: "Trigonometric levelling is the process of determining the differences of elevations of stations from observed vertical angles and known distances. "The vertical angles are measured by means of theodolite. The horizontal distances by instrument Relative heights are calculated using trigonometric functions. 

● This is an indirect method of levelling.

 ● In this method the difference in elevațion of the points is determined from the observed vertical angles and measured distances. 

● The vertical angles are measured with a transit theodolite and The distances are measured directly (plane surveying) or computed trigonometrically (geodetic survey).

 ● Trigonometric levelling is commonly used in topographical work to find out the elevation of the top of buildings, chimneys, church spires, and so on.Also, it can be used to its advantage in difficult terrains such as mountaineous areas. 

● Depending upon the field conditions and the measurements that can be made with the instruments available, there can be innumerable cases

METHODS OF DETERMINING THE ELEVATION OF A POINT BY THEODOLITE: Case 1. Base of the object accessible.

Case 2. Base of the object inaccessible,Instrument stations in the vertical plane as the elevated object.

Case 3. Base of the object inaccessible, Instrument stations not in the same vertical plane as the elevated object.

Case 1. Base of the object accessible

Note :- it means we can easily measures the distance between the object and instrument station .

Where

A= Instrument station.

B= Point to be observed.

h= Elevation of B from the instrument axis

D =Horizontal distance between A. and the base of object.

h1= Height of instrument (H. I.) 

Bs= Reading of staff kept on B.M.

Alpha = Angle of elevation = angle BAC. Then

Hence we can find RL

Case 2. Base of the object inaccessible, Instrument stations in the same vertical plane as the elevated object.

There may be two cases.

(a) Instrument axes at the same level.

 (b) Instrument axes at different levels.

1) Height of instrument axis to the object is lower.

2) Height of instrument axis to the object is higher. 

 

(a) Instrument axes at the same level:-

Then from figure.

From this we can find out RL

contouring in surveying

 contouring in surveying

A contour line is a imaginary line which connects points of equal elevation. Such lines are drawn on the plan of an area after establishing reduced levels of several points in the area. A numerical value placed upon a contour line to denote its elevation relative to a given datum, usually mean sea level is called Contour Value. The contour lines in an area are drawn keeping difference in elevation of between two consecutive lines constant. Alternatively , a contour or a contour line may be defined as the line of intersection of a level surface with the surface of ground. This means every point on a contour line has the same altitude as that of the assumed intersecting surface. The process of tracing contour lines on the surface of the earth is called contouring and the maps upon which these lines are drawn are called contour maps.

The constant vertical distance between two consecutive contours is called the Contour Interval and the horizontal distance between any two adjacent contours is termed as the horizontal equivalent. The horizontal equivalent depends upon the slope of the ground The contour interval of a contour map is the difference in elevation between successive contour lines. For example, Figure shows contours in an area with contour interval of 1 m.

The contour interval depends upon the following factors:

(i) The nature of the ground:

In flat and uniformly sloping country, the contour interval is small, but in broken and mountainous

region, the contour interval should be large otherwise the contours will come too close to each

other.

(ii) The purpose and extent of the survey:

Contours interval is small if the area to be surveyed is small and the maps are required to be

used for the design work or for determining the quantities of earth work etc., while wider

interval shall have to be kept for large areas and comparatively less important works.

(iii) The scale of the map:

The contour interval should be in the inverse ratio to the scale of i.e. the smaller the scale, the

greater the contour interval.

(iv) Time and expense of field and office work:

The smaller the interval, the greater is the amount of field -work and plotting-work.

Characteristics of Contours

• Contour lines must close, not necessarily in the limits of the plan.

• Widely spaced contour indicates flat surface.

• Closely spaced contour indicates steep ground.

• Equally spaced contour indicates uniform slope.

• Irregular contours indicate uneven surface.

•Depression between summits is called a 

saddle. It is represented by four sets of

contours . 

It represents a dip in a ridge or the 

junction of two ridges.

And in the case of a mountain range, it

takes the form of a pass. Line passing

through the saddles and summits gives 

water shed line.

•Contour lines generally do not meet or intersect each other.

•If contour lines are meeting in some portion,

it shows existence of a vertical cliff

In this case, several contours coincide and the 

horizontal equivalent becomes zero.

• If contour lines cross each other,

it shows existence of overhanging

cliffs or a cave.

Errors in Levelling

  Errors in Levelling 

Instrumental errors: Error in permanent adjustment of level: For any major surveying work, instrument needs to be tested and if required, gets to be adjusted. For small works, bubble of the level tube should be brought to the center before each reading and balancing of sights are to be maintained. Staff defective and/or of non-standard quality: The graduation in staff may lack standard distance and thus may cause error in reading. In an ordinary leveling, the error may be negligible but in the case of precise leveling, the graduations are to be standardized with invar tape. Error due to defective level tube: The bubble of the level tube may remain central even though the bubble axis is not horizontal due to its sluggishness or it may take considerable time to occupy central position, if it is very sensitive. Also, there may be irregularity in the curvature of the tube causing delirious effect. Error due to defective tripod: The tripod stand should be strong and stable otherwise it causes setting of the instrument unstable and considerable time is required to make it level. The nuts provided at the joints of the legs to the tripod head should be well-tightened before mounting the instrument. The tripod should be set up on a stable, firm ground.

 Personal errors: Due to imperfection in temporary adjustment of the instrument These errors are caused due to careless setting up of the level, improper leveling of the instrument, lack in focus of eyepiece or/and objective and error in sighting of the staff. Careless set-up of the instrument: If the instrument is not set up firmly, it gets disturbed easily. If the ground is not firm, it may have settled down and on hard ground, it may get slipped.  Imperfect leveling of the instrument: Due to improper leveling of the instrument, bubble does not remain at the center when the sights are taken resulting error in reading. To avoid the error, the bubble should be brought to the center before each reading.  Imperfect focusing. If either the eye-piece or the objective or both are not properly focused, parallax and thus error in the staff readings occur. Due to movement of eyes if there is any apparent change in the staff reading the eye-piece and objective need proper focusing.

Errors in sighting: This occurs when the horizontal cross-hair does not exactly coincide with the staff graduation or it is difficult to see the exact coincidence of the cross hairs and the staff graduations. The error can be minimized by keeping the sight distance small. 

Error due to staff held Non-vertical. If the staff is not held vertical, the staff reading obtained is greater than the correct reading. To reduce the error, the staff should be held exactly vertical or the staff man should be asked to waive the staff towards the instrument and then away from the instrument and the lowest reading should be taken. 

Errors in reading the staff: These errors occur if staff is read upward, instead of downwards, read against the top or bottom hair instead of the central hair, mistakes in reading the decimal part and reading the whole meter wrongly. Errors in recording: The common errors are entering a wrong reading (with digits interchanged or mistaking the numerical value of a reading called by the level man), recording in wrong column, e.g., B.S. as I.S., omitting an entry, entering the inverted staff reading without a minus sign etc. 

Errors in computing: adding the fore sight reading instead of subtracting it and or subtracting a back sight reading instead of adding

Natural errors:

Error due to curvature: In case of small sight distance error due to the curvature are negligible, but if the sight distances are large, the error should be estimated and accounted for, as discussed below. However, the error can be minimized through balancing of sight or reciprocal observation.

 Errors due to wind: Strong wind disturbs leveling of an instrument and verticality of staff. Thus, it is advisable to suspend the work in this condition.

 Errors due to sun: Due to bright sunshine on the objective, staff reading cannot be taken properly. To avoid such error, it is recommended to maintain a shed to the objective. 

Errors due to temperature: Temperature of the atmosphere disturbs setting of parts of instrument as well as causes fluctuation in the refraction of the intervening medium. These lead to error in staff reading. Disturbance caused to instrument may be minimized by placing the instrument under shed. 

Computation of area and volume: Surveying and Leveling: Computation of Areas of Regular Figures

AREAS AND VOLUMES 

In civil engineering works such as designing of long bridges, dams, reservoirs, etc., the area of

catchments of rivers is required. The areas of fields are also required for planning and

management of projects. The area is required for the title documents of land.

In many civil engineering projects, earthwork involves excavation and removal and dumping of

earth, therefore it is required to make good estimates of volumes of earthwork. Volume

computations are also needed to determine the capacity of bins, tanks, and reservoirs, and to

check the stockpiles of coal, gravel, and other material.

Computing areas and volumes is an important part of the office work involved in surveying. 

1. AREAS

 

The method of computation of area depends upon the shape of the boundary of the tract and

accuracy required. The area of the tract of the land is computed from its plan which may be

enclosed by straight, irregular or combination of straight and irregular boundaries.  

1.1 Computation of Areas of Regular Figures

 

When the boundaries are straight the area is determined by subdividing the plan into simple

geometrical figures such as triangles, rectangles, trapezoids, etc. Standard expressions as given

below are available for the areas of straight figures.

(a) Triangle: 

 

Computation of area and volume: Surveying and Leveling: Simpson's Rule

 The main objective of the surveying is to compute the areas and volumes.

Generally, the lands will be of irregular shaped polygons.

There are formulae readily available for regular polygons like, triangle, rectangle, square and other polygons.

But for determining the areas of irregular polygons, different methods are used.

Earthwork computation is involved in the excavation of channels, digging of trenches for laying underground pipelines, formation of bunds, earthen embankments, digging farm ponds, land levelling and smoothening. In most of the computation the cross sectional areas at different interval along the length of the channels and embankments are first calculated and the volume of the prismoids are obtained between successive cross section either by trapezoidal or prismoidal formula.

Simpson’s Rule

Statement

It states that, sum of first and last ordinates has to be done. Add twice the sum of remaining odd ordinates and four times the sum of remaining even ordinates. Multiply to this total sum by 1/3rd of the common distance between the ordinates which gives the required area.

Where O1, O2, O3, …. On are the lengths of the ordinates

d = common distance

n = number of divisions

Note:

This rule is applicable only if ordinates are odd, i.e. even number of divisions.

If the number of ordinates are even, the area of last division maybe calculated separated and added to the result obtained by applying Simpson’s rule to two remaining ordinates.

Even if first or last ordinate happens to be zero, they are not to be omitted from Simpson’s rule.

The following offsets are taken from a chain line to an irregular boundary towards right side of the chain line.

Chainage	0	25	50	75	100	125	150
Offset ‘m’	3.6	5.0	6.5	5.5	7.3	6.0	4.0

Common distance, d = 25m

Area = d/3[(O1+O7) + 2 (O3+O5)+4(O2+O4+O6)]

= 25/3[(3.6+4)+2(6.5+7.3)+4(5+5.5+6)]

Area = 843.33sqm