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Detailed analysis of plane table surveying

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Detailed analysis of plane table surveying

  2. 2. ABSTRACT The main objective of this research paper is to present a deep and specified presentation on plane table surveying. What, how and where is plane table surveying used is explained in detail in these papers. A brief introduction followed by the history and plotting methods and uses and benefits of this type of surveying have been discussed ahead. Also the three main phases of plane table in the time has been discussed. Emphasis is given even to small details regarding types and uses of alidades in plane table surveying. Subjects are supported with good clear images in order for better understanding. The main purpose of writing these papers was to provide a flexible, clear and detail information on one of the oldest surveying methods in the world. Before the advancements in civil engineering and the introduction of modern civil engineering instruments and equipment’s, plane table surveying was the initial and base of surveying. This was one of the widest used methods. A good systematic analysis is done on the topic ahead in these papers. 2
  3. 3. INTRODUCTION Plane table is a graphical method of surveying in which the field works and the plotting is done simultaneously. It is particularly adopting in small mapping. Plane table surveying is used for locating the field computation of area of field. It is particularly adapted for small or medium scale mapping in which great accuracy in detail is not required. A plane table (plain table prior to 1830) is a device used in surveying and related disciplines to provide a solid and level surface on which to make field drawings, charts and maps. The early use of the name plain table reflected its simplicity and plainness rather than its flatness. 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. For quick and approximate surveying, when great precision and accuracy is not needed, plane table surveying techniques is very suitable. It is particularly convenient for filling the details between the stations already fixed and surveyed by more precise method of triangulation or theodolite traversing. For small area surveys, plane table is recommended. The great advantage of this technique is that field work and map plotting is achieved simultaneously by use of graphical surveying. The principle used in plane table surveying is that an unknown point of interest can be established by measuring its directions from known points. 3
  4. 4. BACKGROUND The first known instrument for directly producing a drawing of a site was developed by Johann Richter. He is also known as Johannes Praetorius, a Nuremberg mathematician, born in 1610. Thiscircular table, called atabula praetoriana,mensula praetorianaor Pretorian table, used with a simple alidade and allowed a piece of paper to be slipped under the alidade for drawing. Later the devices adopted a rectangular table and enhanced the type and features of the alidade THE ORIGIN OF ALIDADE 1. An indicator or a sighting apparatus on a plane table, used in angular measurement. 2. A topographic surveying and mapping instrument used for determining directions, consisting of a telescope and attached parts. There are a number of common usages, the main subject of this web page is the map making surveying instrument used on a table that has been leveled. On ships an Alidade is used to measure the angle from the ship's longitudinal axis to some target or targets, typically to helpdetermine the ships position relative to the target(s). Large telescopes have an alidade system that’s used to point in azimuth. These were used on a wooden table that had a drawing attached. The idea was to make a map while in the field using stadia for distance to the rod. 4
  5. 5. WORK DONE: The very early Alidades were just a ruler with sighting wires held in a frame at each end. That was what was used on the Sketch Boards. A compass can be used as an Alidade when a scale is aligned with the North position. The Dietzgen Compass with square scale is in this category and you can get a scale base for some models of the Brunton Com-Pro pocket transits The K&E Early 1800s Alidade appears to be a transit instrument with a vertical angle measuring vernier capability and probably with stadia hairs in the scope so that distance can be manually computed for inclined shots. No compass as part of the Alidade Figure: different type of alidades 5
  6. 6. THE EXPENSION OF THE PLANE TABLE Plane table mapping is a subject that has received minimum attention over the years, but it played a very important role in the history of surveying. The plane table dates to approximately the beginning of the 17th century. Some of the first references to the plane table are found in early survey textbooks. The early plane table was a mapping tool, as opposed to the compass and chain that was a boundary tool. The early plane table dealt mainly with planimetric features and not with vertical elevation. The use and development of the plane table has gone through four distinct changes since about 1600. I will address each one of these plane tables and its use. PLANE TABLE CONSTRUCTION Aplane table consists of a smooth table surface mounted on a sturdy base. The connection between the table top and the base permits one to level the table precisely, using bubblelevels, in a horizontal plane. The base, a tripod, is designed to support the table over a specific point on land. By adjusting the length of the legs, one can bring the table level regardless of the roughness of the terrain. 6
  7. 7. PHASES IN PLANE TABLE: 1.THE FIRST PHASE:- Figure 1. The first alidade was a ruler or scale of brass with fold-down sights. The first plane table consisted of wooden boards placed together to form a table about 14 x 11"mounted on a tripod. A paper or cardboard sheet was placed on top of this board. The planimetric map or traverse was drawn on the paper. The alidade is the item that has gone through the most changes. The first alidade was a ruler or scale of brass with fold-down sights, about the same configuration as compass sights 2. SECOND PHASE:- Figure 2. A 19th century plane table The second phase brought about a name change from plain table to plane table. By the middle to the end of the 19th century, the instrument became in shape and size the plane table most surveyors would recognize (see Figure 2). The alidade now had a telescope. The table was about2' square and was mounted on a tripod with an adjustable mount for leveling and 7
  8. 8. rotating the table to orientate to north. The alidade had a vertical circle to turn a vertical angle and calculate the difference in elevation between points. 3.THIRD PHASE:- THE MODERN ERA Figure 4. Plane table mapping in the field Unfortunately-or fortunately-the total station with data collection made the plane table and alidade into museum pieces. No article would be complete without a mention of the surveyors who utilized plane table boards. There were only a few days each year suited for plane table mapping. The weather needed to be warm but not hot; sweat dripping from your face and hands could make amass of the paper drawing. The USGS used an umbrella over the board when mapping. Surveyors also needed a day with very little wind. And the reflection of the sun off the board would quickly turn your face into old shoe leather. In the winter, your fingers would get stiff from the cold, making it very difficult to draw the map. Bending over the board for eight hours each day without being able to lean on the table took a physical toll on the back. 8
  9. 9. METHODS OF SURVEY: USING PLANE TABLE AND ALIDADESURVEY 1. This is a method of survey that allows a surveyor to plot and create an accurate scale drawing on site. The idea is to scale down the site to a size that fits onto the drawing board. 2. A plane table is a drawing board which is fixed to a tripod, leveled, and orientated. An alidade is a sighting device used to observe the salient points of the site. 3. Have a good look at the site before you start the survey, time should be taken to walk round and have a good look at the site or building that you are going to record. On a building, the obvious features that you would want to record are the corners, door and window openings, fireplaces. More subtle features that you would look out for are changes in wall direction, straight joints, blocked doors or windows, crack slots, changes in the stonework, changes in floor covering, byre drains. STEP 1:-SELECT A SURVEY STATION Once you have had a good look at the site, you will select a position for your survey station from which you have a line of site to as many of the main points as possible. It is particularly important to be able to see all the corners and places where a feature has a change in direction. Set up the tripod legs over your selected survey station. Prepare the drawing board; a piece of polyester drafting film is taped onto the drawing board with masking tape. The corners are taped first, with the film pulled tight, and then the edges are taped. The board is fixed onto the tripod. STEP 2:- ORIENT THE DRAWING BOARD When drawing a building you would orientate the long side of the board so that it is parallel to the long axis of the building. If possible, for a site plan, you would orient the board so that north is up the page. For all plans it is important to check that the whole site is going to fit on the board at your chosen scale. A pin is positioned into the board to give a fixed point from which observations and measurements can be taken. The pin marks the position of your survey station on the board. Once the survey has commenced the plane table should not be moved. 9
  10. 10. STEP 3:- CARRY OUT THE SURVEY The alidade is placed against the pin and used to observe in turn, selected points. Rays are drawn on the film and measurements between the pin and the points taken with the 30mtape. The measurement is written onto the drawn ray as a record. Subsequently, each point is plotted along the ray at the selected scale, ' with a scale rule. Observations and measurements are taken to as many points as required to allow the shape to be recorded. These plotted points create an accurate framework around which the rest of the plan can be constructed. This method is most useful for plans of single buildings or small siteswithin a radius of 30m from the plane table. EQUIPMENT REQUIRED FOR A PLANE TABLE ANDALIDADE SURVEY:Plane table, tripod legs, alidade, spirit level, 30m tape, polyester drafting film, hi-polymer 6H pencil, masking tape, pin, scale ruler, compass, ranging rod for sighting, plumb bob. EXAMPLE OF PLANE TABLE SET UP:- 10
  11. 11. EXAMPLE OF DRAWING PAPER AFTER ALIDADE SURVEY:- MERITS AND DEMERITS Merits: 1. 2. 3. 4. 5. 6. 7. It is most suitable for preparing small scale map or surveying small area. It is most rapid method. Field book is not necessary. No great skill is required for satisfactory map. It is particularly suitable for magnetic area where prismatic compass is not reliable. Contour and irregular object may be represented accurately. It is less costly. Demerits: 1. 2. 3. 4. Plane Table Essentially a tropical instruments. It is not suitable to work in wet climate. There are several accessories to be carried out and therefore they are likely to be lost. It is not suitable for accurate work. 11
  12. 12. CONCLUSION As all we know that the use of total station have made the plane table and alidade intomuseum pieces because of the technology changes during 19th century .The aim of using the plane table is to show how the traditional way to use the alidade without the help of thetheodolite and the total station while drawing and plotting the points on the drawing paper .We should be thankful because of the scientist that has made a lot of experimentduring inverting the alidade and the theodolite to use with the plate table. Now, modernsurveyor can use the total station as their main instrument but they will never forget what is plane table is about. REFERENCES The following sites, blogs and research papers have been referred in order to complete this report www.agriinfo.in www.wikipedia.com www.scribd.com www.google.com www.brittanica.com www.alhea.com 12