Land Surveyor Forum

Replies

• Student Surveyor

  Dave Drahn May 31, 2016 at 10:06pm

  Are you talking about using the compass rule to adjust a traverse?
• Student Surveyor

  Mat Win November 10, 2014 at 10:35pm

  thanks Thomas and Michael

  Awesome feedback thanks again

  Cheers Mat
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  Ian Peter Izzett November 4, 2014 at 2:34am

  Michael Allan Sanchez has presented a good description of how to go about measuring an angle. Its interesting to compare the "survey talk" from the USA compared with southern Africa. I'm impressed at the number of similarities, while noting that there are many differences.
  Michael refers in No 7, to the telescope in "normal" position, and "inverted" or "plunged". For a rookie looking at a theodolite (or total station), it would be difficult to judge weather the telescope is "normal" or "inverted". Here is a suggestion to clarify. We use the terms "Face Left" (FL) or "Face Right" (FR) instead. These terms refer to the side on which the vertical circle is while taking a reading. The vertical circle is housed inside a circular housing incorporated on one of the standards supporting the horizontal axis of the telescope, even on a total station.
  • Land Surveyor

    Ivan Maleev > Ian Peter Izzett June 15, 2016 at 3:43am

    It is interesting to read about work in another countries. In Russia we use terms "circle is right", "circle is left" it mean's side of vertical circle.
• Land Surveyor

  DEWARD BOWLES November 3, 2014 at 7:15pm

  Good answers and I am happy to see several educated Land Surveyors I know responding.
  Thomas it has been a long time and Michael your always packing the heat as usual.
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  Michael Alan Sanchez November 3, 2014 at 4:14pm

  Points on the ground or on a map are related to each other through a horizontal distance and a horizontal angle (or direction.) Horizontal angular measurements are made between survey lines to determine the angle between the lines. A horizontal angle is the difference between two measured directions. Horizontal angles are measured on a plane perpendicular to the vertical axis (plumb line).

  Vertical angular measurements are measured to determine slope of survey lines from the horizontal plane (level line). When the vertical angle is applied to the slope distance, the horizontal and vertical distances may be calculated. Vertical angles are measured on a plane passing through the vertical axis perpendicular to the horizontal plane. In order to facilitate the trigonometric calculations of horizontal and vertical distance, the reference or zero angle is on the vertical axis directly above the instrument, which is termed the zenith angle.

  In the United States, the sexagesimal system of angular measurement is used. In the sexagesimal system, there are 360° in the circumference of a circle. The basic unit is the degree (°), which is further divided into 60 minutes (60'), and the minute is subdivided into 60 seconds (60"), and decimals thereof. Other angular unit systems utilize 400^g (grads) or 2p Radians per complete circle (360°).

  3.6.2 Terms

  The following terms are defined specifically for angular measurement. Their meanings may differ slightly in other contexts.

  1. A pointing consists of a single sighting and circle reading on a single object.
  2. An angular observation is a single, unadjusted determination of the size of an angle. A single angular observation is derived by subtracting the value of a pointing on a reference object from the value of a pointing on an observed station.
  3. An angular measurement is the final determination of the magnitude of an angle before adjustment. Minimum angular measurement is the mean of at least two observations, one in the direct mode and the other in the reverse mode.
  4. A reference object (RO) is a survey point that is used as an initial sight for orientation when measuring horizontal angles and "directions". The term, RO, will be used interchangeably with backsight (BS) in this manual.
  5. A direction is the value of a clockwise angle between a backsight and any other survey point. The reference direction to the backsight can be either arbitrary or set to a desired value.
  6. Setting a position is the act of setting a specified horizontal circle reading while the telescope is pointed toward a reference object. Generally, either zero degrees or the calculated "back azimuth" is used.
  7. A direct reading is with the telescope in the upright (normal) position. An inverted or reverse reading is with the telescope inverted or plunged.
  8. Turning a position is the act of making one direct and one reverse observation on each survey point to which a direction is required.
  9. A repetition is a single observation (in a series of observations) of a horizontal angle, made with a repeating theodolite. This type of theodolite is rarely used nowadays. Information about repeating theodolites can be found in surveying textbooks.
  10. Indirect measurement of an angle is a computed value of the angle from other data. For example angles of a triangle can be computed from distance measurements of its three sides. Orientation of the triangle is established by selected sides whose directions are known or measured.

  3.6.3 Errors, Corrections, and Precautions

  Direct measurement of angles and line direction by total station, theodolite, compass, or transit is familiar to all surveyors. However, many surveyors are not completely familiar with specific procedures that will achieve specified results. This section discusses errors involved in angular measurements and outlines procedures that will enable the surveyor to achieve specified results.

  As mentioned earlier, errors in a measurement stem from various sources. Generally, angular measurements can be impacted by four classes of errors. These four classes are: instrumental, personal, natural, and miscellaneous errors. In the subsequent sections these factors and how to minimize them are discussed in detail

  http://www.state.nj.us/transportation/eng/documents/survey/Chapter3...

  One usually closes the polygon so the total sum of  interior angles is the number of sides -  2 X 180 degrees, distributing the error by various methods including just dividing by the number of angles and adding or subtracting the result from the raw angles.  Then a traverse is calculated using Cartesian coordinate method to calculate a mathematical error of close, this too can be distributed by various methods, usual transit, compass or least squares.  If the error indicates and error, on can traverse in the reverse direction and often find the error if it is in one setup.
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  Chris Little November 3, 2014 at 4:06pm

  I'm with you Doug, I do not understand what question Mat is asking, even less Thomas' answer!!

  An horizontal angle is the difference between two telescope pointings taken from the theodolite/total station circle, or the vertical angle of the telescope pointing referenced to the horizontal or zenith direction. The raw observations being reduced to give an angle. If a direction is known or an arbitrary value taken then the angle can be related to those.
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  Doug Tarrant November 3, 2014 at 3:20pm

  I've been suveying for coming up 46 years. In other words being old and grumpy means I struggle to come to grips with each new fangled tool and the associated modern speak. I used to be able to speak fluent survey talk but the question posed has me baffled. What on earth is the question about? Further, Thomas, I'm sorry but your answer does not shed any light.

  I see there are 131 views of this post but only one reply, two including this one. Maybe I'm not alone.
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  Thomas S McGrath November 3, 2014 at 1:24pm

  Raw angular data cannot be understood or used if we do not define what a measurement is. In order to have an angle; one must have a sigma value. This is not done in the in an electronic data collector. do not use them for making an angular measurement as they can only produce a scaling , whichillegal when locating real property evidence.