Compass Surveying: An Overview

Compass surveying is the branch of surveying in which the position of an object is located using angular measurements determined by a compass and linear measurements using a chain or tape. Compass surveying is used in following circumstances:

  • If the surveying area is large, chain surveying is not adopted for surveying rather compass surveying is employed.
  • If the plot for surveying has numerous obstacles and undulations which prevents chaining.
  • If there is a time limit for surveying, compass surveying is usually adopted

Prismatic compass ( brasscompass.com)

Compass surveying is not used in places which contain iron core, power lines etc which usually attracts magnets due to their natural properties and electromagnetic properties respectively. Compass surveying is done by using traversing. A traverse is formed by connecting the points in the plot by means of a series of straight lines.

Magnetic compass

Magnetic compass is used to find out the magnetic bearing of survey lines. The bearings may either measured in Whole Circle Bearing (W.C.B) system or in Quadrantal Bearing (Q.B) system based on the type of compass used. The basic principle of magnetic compass is if a strip of steel or iron is magnetized and pivoted exactly at centre so that it can swing freely, then it will establish itself in the magnetic meridian at the place of arrangement.

Major types of magnetic compass are:

  1. Prismatic compass
  2. Surveyor’s compass
  3. Level compass

Prismatic compass

Prismatic compass is a portable magnetic compass which can be either used as a hand instrument or can be fitted on a tripod. It contains a prism which is used for accurate measurement of readings. The greatest advantage of this compass is both sighting and reading can be done simultaneously without changing the position.

Prismatic compass ( Geology Superstore)

Major parts of a Prismatic Compass are:

  • Magnetic needle
  • Graduated ring
  • Adjustable mirror
  • Sliding arrangement for mirror
  • Object vane
  • Eye vane
  • Metal box
  • Glass cover
  • Horse hair

Adjustments of prismatic compass

Two types of adjustments:

  1. Temporary adjustment
  2. Permanent adjustment

Temporary adjustments

    • Centering: it is the process of fixing the compass exactly over the station. Centering is usually done by adjusting the tripod legs. Also a plumb-bob is used to judge the accurate centering of instruments over the station.
    • Leveling: the instrument has to be leveled if it is used as in hand or mounted over a tripod. If it is used as in hand, the graduated disc should swing freely and appears to be completely level in reference to the top edge of the case. If the tripod is used, they usually have a ball and socket arrangement for leveling purpose.
  • Focusing the prism: Prism can be slide up or down for focusing to make the readings clear and readable.

Permanent adjustments are same as in the Surveyor’s compass.

Surveyor’s compass

Surveyor’s compass consists of a circular brass box containing a magnetic needle which swings freely over a brass circle which is divided into 360 degrees. The horizontal angle is measured using a pair of sights located on north – south axis of the compass. They are usually mounted over a tripod and leveled using a ball and socket mechanism.

Surveyor’s compass (National Museum of American History)

They also have two types of adjustments, temporary and permanent. Temporary adjustments are same as described in prismatic compass.

Permanent adjustments

They are done only in the circumstances where the internal parts of the prism is disturbed or damaged. They are:

  • Adjustments in levels
  • Adjustment of pivot point
  • Adjustment of sight vanes
  • Adjustment of needle

Measurement of angles and Computation of area

The observations of a plot using compass surveying will be:

Here the bearings are observed in Whole Circle Bearing (W.C.B) system.

Line Fore bearing Distance measured (m)
AB 40˚ 0’ 10.8
BC 110˚0’ 8.2
CA 280˚0’ 13.1

Surveying Triangular area with compass survey

Included angle = bearing of previous line – bearing of next line

= (280˚-180˚) -40˚ =60˚00’

00’

Sum= 180˚00’

Check: (2n-4) 90˚= (6-4) 90˚=180˚

Where n = number of sides of the traverse

Area Computation

Surveying Triangular area with compass survey area

Advantages & Disadvantages of Compass surveying

Advantages

  • They are portable and light weight.
  • They have fewer settings to fix it on a station
  • The error in direction produced in a single survey line does not affect other lines.
  • It is suitable to retrace old surveys.

Disadvantages

  • It is less precise compared to other advanced methods of surveying.
  • It is easily subjected to various errors such as errors adjoining to magnetic meridian, local attraction etc.
  • Imperfect sighting of the ranging rods and inaccurate leveling also causes error.

Errors in compass survey

Errors can be arising due to various reasons during the process of surveying, they are classified as:

  • Instrumental errors
  • Personal errors
  • Natural errors

Instrumental errors

As the name suggests they are arise due to the wrong adjustments of the instruments. Some other reasons are:

  • If the plane of sight not being vertical, it causes error in sighting and reading.
  • If the magnetic needle is not perfectly straight or if it is sluggish, readings may not be accurate.

Personal errors

They arise mainly due to the carelessness of the surveyor. They are:

  • Inaccurate leveling
  • Inaccurate reading
  • Inaccurate centering

Natural errors

Natural errors are occurring due to the various natural causes which affect the working of compass. It has nothing to do with the surveyor and to minimize them, some corrections in calculations applied. They are:

  • Local attraction
  • Proximity to the magnetic storms
  • declination

Open Traverse

Closed Traverse

 

Closing Error

Source(s):

EngineeringCivil.Org

Posted in Class Notes, earth, Geography Practicals/Lab and Statistical Techniques | 1 Comment

Communalism: A Dangerous Ideology

  • Communalism, in a broad sense means a strong attachment to one’s own community. In popular discourse in India, it is understood as unhealthy attachment to one’s own religion.
  • It’s an ideology that, in order to unify the community, suppresses distinctions within the community and emphasizes the essential unity of the community against other communities.
  • In this way it promotes belief in orthodox tenets and principles, intolerance and hatred of other religions and thus, divides the society.
  • Positive aspect of communalism stands for the affinity of an individual towards his own community involving efforts for the social and economic upliftment of his community.
  • However, in negative connotation, it is an ideology which emphasises the separate identity of a religious group in relation to other groups with a tendency to promote its own interests at the expense of the others.

Communalism is a dangerous ideology that promotes the false belief that one group, particularly one religious group, has more differences than similarities with outside groups.

An Ideology

Communalism, like most ideologies, is a school of thought shared by a specific group of people. Specifically, communalism is the shared belief within a particular culture that promotes religious and secular isolation from another group. In other words, communalism is a form of segregation, only it’s segregation that the group being segregated actually chooses. In theory, there are many different reasons a group could become communalist, but typically these groups resort to isolating themselves based on religion.

A communalist group believes that their loyalty should lie within the group that they’re a part of above any other loyalty, like nationalism (or loyalty to a country), because their ideals and beliefs don’t match those of other groups. Many communalist groups even believe that they’re a nation of separate confederacies rather than part of the country in which their members actually reside.

Often, the trouble with communalism is that each group denies the fact that they have more commonalities with other groups than they have differences. This can result in groups becoming hostile to one another, which has given communalism negative connotations. But it’s important to remember that it’s not always the groups themselves that originally instituted the ideology of communalism. In India, for example, much of the communalism (and resulting inter-group conflict) between the Muslims, Sikhs, Hindus and Christians was initially promoted by the British. Seems like a strange thing for a government to do, right? Let’s explore why.

Colonization & Government Control

Communalism didn’t really become an ideology until the British colonization of India, making it a fairly modern concept. It got started after the British realized that when they promoted nationalism, minority groups might realize they had shared interests, become more dominant, and resist British control of India, which could have led to another revolt like the Revolt of 1857. So instead of promoting nationalism, the British encouraged groups to essentially isolate themselves from and reject other religious groups.

This is not an uncommon practice even today, and even outside of colonial governments. For example, the American political system, especially during political campaigns, is notorious for promoting fear in an effort to win votes. Candidates often exploit the differences between cultures, effectively dividing the population. This is especially dangerous because it can evolve into fundamentalism.

Progression of Communalism

Minorities ended up being shut out of government, since education was essential for government positions and Hindus were more educated than Muslims. With fewer men in government and trade and industry, the minorities continued to be exploited and controlled, which made them feel a greater need to protect themselves as a group, tightening the influence of communalism.

Communalism is a shared ideology within one group that promotes the isolation of that group from others. Essentially, it’s a form of self-segregation that hinges on a group’s belief that is has more differences than similarities with other groups of people.

In India, communalism was originally promoted by the British colonizers after the Revolt of 1857 in an effort to keep groups from joining together to fight British rule. Within India today, the concept of communalism is apparent in divisions between Hindus, Christians, Sikhs and Muslims.

Source(s):

Study.com

Drishti IAS

Posted in Class Notes, earth, society | Leave a comment

Urban Forms: Evolution and Future City Planning

Urban spaces are pretty important part of human history.

Kinds of Urban Forms

Cities are loud. They are crowded. Parking is expensive. So, why do so many love them? Regardless of your personal feelings, urban centers have been of tremendous importance throughout world history. Urban spaces are products of pure human innovation, reflecting the unique human ability to transform landscapes to increase our chances of survival, happiness, and comfort. But what matters isn’t just that we embark on this transformation; it’s how we carry it out. The physical patterns, layouts, and structures that make up an urban center are collectively called the urban form. As the most basic canvas upon which settled human societies are built, urban forms are critical to both our daily lives right now and our interpretations of past cultures.

Before we delve into our brief history of urban forms, let’s talk a little more about the term. Urban forms are ever changing, adapting with every new building, park, sidewalk, road, or gate that’s erected. As urban forms develop and change, we can identify two major variations. An organic urban form is one that develops without centralized planning. Nobody tells people where to put houses, or which way the city gate should face. In contrast, a planned urban form is designed and coordinated. The ways that urban centers grow, whether in organic or planned ways, can tell us a lot about the attitudes, beliefs, lifestyles, and influences of people who live there.

Origins of Urban Form

Our story begins up to 12,000 years ago during a period called the Neolithic Revolution. This period saw the earliest experiments with agriculture. Agriculture allowed people to stay in one place throughout the year and build permanent structures.

As people settled down, they developed the first urban societies. We assume that most of these arose organically, but it did not take people long to develop planned urban centers. The first true cities developed in the Middle East between 4500 and 3500 BCE and were very carefully organized. Many cities were enclosed within walls, with formal entrances and defined places for markets, temples, and royal homes.

Advanced City Planning

As cities grew larger and larger, many tried even harder to plan out the shapes, forms, and compositions of their urban spaces. Ancient Greece and China both developed the practice of dividing cities into uniform blocks or municipal units. This was often used to try to control the behaviors of citizens. Some parts of town could only be used for specific economic, religious, or leisure activities. Often, neighborhoods were built only for people of certain levels of education, wealth, or power. By doing this, the city became a more controlled space.

The ancient Greeks and Romans both put so much effort into their city planning that certain urban forms almost became synonymous with their civilizations. The Romans in particular established routine urban forms. This was very important to them. Whenever they expanded their empire and tried to bring Roman society into a new area, they did so first and foremost by building a Roman-style city.

Medieval Urban Forms

After the fall of Rome, European societies of the medieval period gave up on formal urban planning. New cities had more organic forms, with people building and adding to the cities as needed. This gave many cities a jumbled but natural feel as space was used in practical ways.

By the rise of the Renaissance in the 15th century, patterned urban forms once again became popular. Cities of the time were growing, and architects attempted to find ways to bring order to the organic forms of previous centuries. Many European cities today are defined by a mixture of patterned and organic spaces that overlap and connect again and again. Of course, as this was happening in Europe, colonists to other places took these ideas with them. Both patterned and organic urban forms found their ways into the colonies of the Americas.

After the Industrial Revolution

The next major period of growth for cities came with the Industrial Revolution of both the 18th and 19th centuries. The introduction of industrial technologies added a new element to traditional urban forms: factories. Factories separated people into classes of owners and workers, and helped keep these two groups separated.

From the 19th through 20th centuries, urban forms reflected many changing social patterns, particularly in the United States. At some periods, people flocked to the cities. At other times, the majority retreated to the suburbs, developing a new form of urban space there. Around the world, our urban centers continue to change along with our lifestyles and ideas, and for as long as we can tolerate the city, it will keep on moving with us.

Urban spaces are important parts of human societies and histories. As purely constructed places, the physical shapes and components of urban centers can tell us a lot about people. Collectively, we call the physical patterns, layouts, and structures of an urban center its urban form. Sometimes urban spaces are organic, formed without centralized planning and developing as needs dictate. Organic urban forms appeared in the first settled communities, after the fall of Rome, as well as at several points in between. However, many cities are also planned. Planned urban forms were very important to the ancient Greeks and Romans, as well as to the people of the Renaissance and Industrial Revolution. Throughout history and across the world, our cities have been pretty important. Even if the parking is expensive.

Links and Source(s):

Study.com

Medieval Indian Cities

Posted in earth, urban morphology, Urban Studies | Leave a comment

Sect And Cult: Concepts and Differences

The word sect comes from the Latin word secta, which means “school of thought.” It is a subjective term that may apply to religious faith or denomination, or it may refer to a heretical splinter group. Sometimes, the connotation is one of disapproval, similar to the “destructive heresies” spoken of in though there are no consistent or accepted exemplars to use to identify a sect.

Sects are found in all religions. Islam has Sunnis and Shias, Judaism has Orthodox and Karaites, Hinduism has Shiyaism and Shaktism, and Christianity has Baptists and Lutherans. These are all examples of religious sects, and they can be thought of as “branches” of different religions. There are also non-religious sects, such as capitalists and socialists among economists, or Freudians and Jungians among psychiatrists.

In contradistinction, the word cult always carries a negative connotation. There are specific criteria used to identify a cult. In Combatting Cult Mind Control, deprogrammer Steven Hassan singles out what he refers to as “destructive cults,” which he defines as “a pyramid-shaped authoritarian regime with a person or group of people that have dictatorial control. It uses deception in recruiting new members (e.g. people are NOT told upfront what the group is, what the group actually believes and what will be expected of them if they become members).” Hassan also correctly points out that cults are not only religious; they may also be commercial or secular in nature.

Hassan developed the BITE acronym, which describes the components employed by destructive cults using mind control. BITE covers the following areas of control:

Behavior Control: An individual’s associations, living arrangements, food, clothing, sleeping habits, finances, etc., are strictly controlled.

Information Control: Cult leaders deliberately withhold or distort information, lie, propagandize, and limit access to other sources of information.

Thought Control: Cult leaders use loaded words and language, discourage critical thinking, bar any speech critical of cult leaders or policies, and teach an “us vs. them” doctrine.

Emotional Control: Leaders manipulate their followers via fear (including the fear of losing salvation, fear of shunning, etc.), guilt, and indoctrination.

From a Christian perspective, a cult is any group that follows teachings that contradict orthodox Christian doctrine and promote heresy. Under this definition, the Watchtower Society and the Latter-day Saints (Mormons) are both cults.

Source(s):

Got Questions

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