Post a Comment Share your views or discuss. Menu twitter facebook. Azimuths and Bearings in Surveying and their Comparison. Azimuths are horizontal angles observed clockwise from any reference meridian. In plane surveying, azimuths are generally observed from north, but astronomers and the military have used south as the reference direction.
Examples of azimuths observed from north are shown in Figure 1. Azimuths may be geodetic, astronomic,magnetic, grid, record, or assumed, depending on the reference meridian used. To avoid any confusion, it is necessary to state in the field notes, at the beginning of work, what reference meridian applies for azimuths, and whether they are observed from north or south.
Azimuths can be read directly on the graduated circle of a total station instrument after the instrument has been oriented properly. This can be done by sighting along a line of known azimuth with that value indexed on the circle, and then turning to the desired course.
Azimuths are used advantageously in boundary, topographic, control, and other kinds of surveys, as well as in computations. Bearings are another system for designating directions of lines. The bearing of a line is defined as the acute horizontal angle between a reference meridian and the line.
The letter N or S preceding the angle, and E or W following it shows the proper quadrant. Thus, a properly expressed bearing includes quadrant letters and an angular value.
In Figure 2, all bearings in quadrant NOE are measured clockwise from the meridian. Geodetic bearings are observed from the geodetic meridian, astronomic bearings from the local astronomic meridian, magnetic bearings from the local magnetic meridian, grid bearings from the appropriate grid meridian, and assumed bearings from an arbitrarily adopted meridian.
The magnetic meridian can be obtained in the field by observing the needle of a compass, and used along with observed angles to get computed magnetic bearings.
Back bearings should have the same numerical values as forward bearings but opposite letters. Because bearings and azimuths are encountered in so many surveying operations, the comparative summary of their properties given in Table 1 should be helpful.
Bearings are readily computed from azimuths by noting the quadrant in which the azimuth falls, then converting as shown in the table.In navigationbearing is the horizontal angle between the direction of an object and another object, or between it and that of true north. The bearing consists of 2 characters and 1 number: first, the character is either N or S. Next is the angle value. Third, the character representing the direction of the angle away from the reference ray - thus, either E, or W. The angle value will always be less than 90 degrees.
An azimuth is specified in the same angle units. A bearing can be taken on another vessel to aid piloting. If the two vessels are travelling towards each other and the relative bearing remains the same over time, there is likelihood of collision and action needs to be taken by one or both vessels to prevent this from happening.
A bearing can be taken to a fixed or moving object in order to target it with gunfire or missiles. This is mainly used by ground troops when planning on using an air-strike on the target. A true bearing is measured in relation to the fixed horizontal reference plane of true norththat is, using the direction toward the geographic north pole as a reference point, while a magnetic bearing is measured in relation to magnetic norththat is in relation to the north direction of the Earth's magnetic field lines at the given location.
The latter is not the same as the direction toward the magnetic north pole due to magnetic anomalies. A grid bearing is measured in relation to the fixed horizontal reference plane of grid norththat is, using the direction northwards along the grid lines of the map projection as a reference point, while a compass bearingas in vehicle or marine navigation, is measured in relation to the magnetic compass of the navigator's vehicle or vessel if aboard ship.
It should be very close to the magnetic bearing. A relative bearing is one in which the reference direction is straight ahead, where the bearing is measured relative to the direction the navigator is facing on land or in relation to the vessel's bow aboard ship. If navigating by gyrocompassthe reference direction is true northin which case the terms true bearing and geodetic bearing are used. In stellar navigationthe reference direction is that of the North StarPolaris. Generalizing this to two angular dimensions, a bearing is the combination of antenna azimuth and elevation required to point aim an antenna in a given direction.
The bearing for geostationary satellites is constant. The bearing for polar-orbiting satellites varies continuously. Moving from A to B along a great circle can be considered as always going in the same direction the direction of Bbut not in the sense of keeping the same bearing, which applies when following a rhumb line.True Meridian vs Magnetic Meridian. A great circle, which passes through true north and true south is known as meridian.
A circle described by the intersection of the surface of the earth with the plane passing through the centre of the earth is known as great circle.
That is, great circle is a circle traced on the surface of a sphere earth is considered as a sphere such that, both have the same diameter. The 0 degree meridian is known as the prime meridian, from which other meridians or lines of longitude are measured, that passes through Greenwich England.
The direction given by the acute angle between a line and a meridian is known as bearing.
The direction from any point along a meridian towards the North Pole of the earth is defined as true north. True north is also known as geographic north. True south is also defined in a similar manner. True meridian is defined as the plane that passes through true north poles and true south poles at the place of observation. True meridian can be established by astronomical observation as it passes through true north and south.
True bearing is the horizontal angle between true meridian and a line. The magnetic north is the direction indicated by a freely suspended and balanced magnetic needle. Magnetic meridian is the line that is parallel to the direction taken by a freely moving magnetized needle. The angle between magnetic meridian and true meridian is known as magnetic declination.
A line having zero declination is known as Agonic line. The lines that have the same declination are known as Isogonic lines.
Magnetic bearing is the horizontal angle between magnetic meridian and a line. What is the difference between True Meridian and Magnetic Meridian? Coming from Engineering cum Human Resource Development background, has over 10 years experience in content developmet and management.Compass survey, Bearing,WCB and QBS ,true and magnetic meridian in hindi
Comments really a nice article…. Leave a Reply Cancel reply.In this post, we are going to discuss about the bearing in surveying and its designation.
The direction of a survey line can either be established with relation to each other or with relation to any meridian. The first will give the angle between two while the second will give the bearing of the line. Bearing of a line is its direction relative to a given meridian.
A meridian is any direction such as true meridian, magnetic meridian and arbitrary meridian. True meridian through a point is the line in which a plane, thus passes through the true north and south poles, intersects with the surface of the earth. It thus passes through the true north and south. The direction of the true meridian through a point can be established by astronomical observations.
True Bearing : True bearing of a line is the horizontal angle which it makes with the true meridian through one of the extremities of the line. Since the direction of the true meridian through a point remains fixed, the true bearing of a line is a constant quantity.
The magnetic bearing through a point is the direction shown by a freely floating and balanced magnetic needle free from all other attractive forces. The direction of magnetic meridian can be established with the help of a magnetic compass. Magnetic bearing : The magnetic bearing of a line is the horizontal angle which it makes with the magnetic meridian passing through one of the extremities of the line.
A magnetic compass is used to measure it. Arbitrary meridian is any convenient direction towards a permanent and prominent mark or signals, such as a church spire or top of a chimney. Such meridians are used to determine the relative positions of lines in a small area. Arbitrary bearing : Arbitrary bearing of a line is the horizontal angle which it makes with any arbitrary meridian passing through one of the extremities. A theodolite or sextant is used to measure it.
The common systems of notation fo bearings in surveying are whole circle bearing system or Azimuthal bearing system and Quadrantal bearing. In this system, the bearing of a line is measured with magnetic north in a clockwise direction. The value of the bearing thus varies from 0 degrees to degrees. Prismatic compass is graduated in this system.
In this system, the bearing of a line is measured eastward or westward from north or south, whichever is neared.
Thus, both north and south are used as reference meridians and the direction can be either clockwise of anticlockwise depending upon the position of the line. In a quadrantal bearing system, the quadrant in which lines lies will have to be mentioned. These bearings are observed by surveyors compass. Join Whatsapp. Skip to content Surveying.
November 17, November 17, ReadCivil 0 Comments. Bearing in surveying- Types and designation In this post, we are going to discuss about the bearing in surveying and its designation.
Bearing in surveying Bearing of a line is its direction relative to a given meridian. Notify of.I am really confused for how to convert back and forth in between these three, declination, magnetic bearings and true bearings. If I look now at the Cuomo book, Example 4. I am confused which is it. I get confused also in the directions, E or W.
Don't memorize formula. Think it in a logical fashion.
Difference Between Whole Circle Bearing and Quadrantal Bearing
If magnetic declination is given, say 10 degree west, then the magnetic north will be 10 degree west to the true north. Now, if magnetic bearing is given, say North 50 degree west, then from the previously calculated or drawn magnetic north go 50 degree further west. This will be your magnetic bearing. Next, to find true bearing, calculate or find the angle between true north and magnetic bearing, which in this case will be 10 degree plus 50 degree to the west of magnetic north.
So it will be north 60 degree west. Take another example, a magnetic bearing of south 55 degree east is provided and the declination is given as 15 degree east and you are asked to find true bearing.
First draw the magnetic north by going 15 degree east of true north. From the magnetic south go 55 degree east to have your magnetic bearing of. Now, in order to find true bearing, you have to see the direction of true south, which in this case is 15 degree east.
So, now subtract 15 degree from 55 degree. So, the true bearing will be south 40 degree east. I view this type of problem as looking at the card on a ship's compass. True north is fixed at the top of the compass. The magnetic declination and the magnetic bearing are marked on the rotating compass card.Or maybe not. But to press on: When one undertakes to write upon a particular subject, one of the time-honored cop-outs one may resort to is to quote a dictionary definition.
They are both valid definitions in proper context. To cut to the chase, we can make a list of four kinds of north. The difference is basically the deflection of the vertical for a particular point, a value we can readily see on a data sheet for a National Spatial Reference System NSRS point. More to the point for this discussion, they are close enough that we can consider them the same.
After all, the differences in the other versions of north will be measured in degrees and minutes. Magnetic North The important thing to keep in mind with magnetic north is that there is a difference, usually of several degrees, between magnetic north and geodetic north, depending on location. Magnetic north is not a chunk of magnetized material buried up somewhere in Hudson Bay. It just happens to coincide well enough with—shall we say it?
And it just so happens that many original surveys upon which we depend used compass directions as a primary tool. Therefore, we surveyors, who are pledged to walk in the footsteps of the ones who originally surveyed before us, owe special respect to bearings that were derived from magnetic north.
Grid North Grid north, on the other hand, is a creation of an individual system, typically State Plane Coordinates. For example, in an ordinary SPC zone, a central meridian is adopted as north.
All other points in that zone use the same line of direction as north, even though the various points would have different convergences. Only at the central meridian would grid north agree with true north.
Classification of Bearings | Surveying
If a point is east of the central meridian, then grid north is east of true north. This means that a given azimuth at a point east of the central meridian, expressed in grid terms, would be a smaller value than that same azimuth expressed in terms of true north. So the convergence value is negative.
In this exaggerated example, the dotted lines represent directions toward true or geodetic, or astronomic north. The lines XY and AB are determined to be parallel on the ground.
Obviously, the angle to XY is much smaller than the angle to AM. But the lines XY and AB are supposed to be parallel. Thereby we see the logic in accepting a grid system for local surveying purposes. Plant North The grid north model can be adapted to a very localized, limited area. At about that same time, Austin had decided as a city to develop a new airport and had actually begun work on a site northeast of town.Due to changes in this version of the forum software, you are now required to register before you may post.
Login or Sign Up. Logging in Remember me. Log in. Forgot password or user name? Posts Latest Activity. Page of 2. Filtered by:. Previous 1 2 template Next. Hello all, I have a property survey that has in the following format S89degrees 17' 49"W on two points on the survey Tags : None.
Re: convert coordinates on a property survey to a compass direction. Originally posted by Unregistered View Post. Comment Post Cancel. Re: convert coordinates on a property survey to a compass direction Thanks for making this site available.
Bearing in Surveying- Definition, Types and Designation of Bearing
It makes problems seem much easier to understand! Re: convert coordinates from a surveyor's bearing to a compass bearing Pls convert the following coordinates from a surveyor's bearing to a compass bearing They are degree, degrees, degrees, degrees and finally degrees I'll be very grateful to get the answers as soon as possible. Re: convert coordinates from a surveyor's bearing to a compass bearing.
Pls convert the following coordinates from a surveyor's bearing to a compass bearing They are degree, degrees, degrees, degrees and finally degrees I'll be very grateful to get the answers as soon as possible. Re: convert coordinates on a property survey to a compass direction "Surveyors usually use true north as a reference, compass, magnetic north, so you have to know local variation. First, in addition to true and magnetic north, a survey may also utilize State Plane Coordinates which yields 'grid north' or many surveys utilize an 'assumed north'.
If indeed the surveyors bearing is a true bearing you would need to know your approximate latitude and longitude so you could find the declination using an on-line tool such as NOAA National Geophysical Data Center Magnetic Field Calculator on-line tool sorry, site won't let me post link If the surveyors bear was already a magnetic bearing you would need to know your latitude and longitude, the year it was surveyed so you could find the declination for that year and the declination for the present date and then determine the difference.
If the surveyors bearing is grid, you could approximate the true bearing using the National Geodetic Survey Geodetic Tool Kit State Plane Coordinate on-line tool sorry, this site won't let me post link by adding or subtracting as appropriate the convergence angle and then prceeding as above with the instuction for a true bearing.