VALUES OF PLANE-TABLE METHOD

Figure 9-8.-Plane-table notes. - 14071_183

Engineering Aid 2 - Intermediate Structural engineering guide book
Page Navigation
167

direction and distances to establish positions. This method of point location is illustrated in figure 9-7. After you set up and orient the plane table at the first station, you draw the direction to the next point on the survey with a radiating ray. The distance between the occupied station and the new point is measured and plotted along the ray. The new plotted position is now considered a known position and can be occupied and used as the next station on the line. The plane table is setup and oriented over this station and another radiating ray is drawn to the next point. This process continues for the length of the traverse. Orientation plays an important role in plane-table traverse. Slight errors in direction at each setup can accumulate rapidly and become large in a short time. Long traverses should be avoided except in reconnaissance surveys. VALUES OF PLANE-TABLE METHOD Advantages of the plane-table method of topographic surveying are as follows: 1. The map is made directly in the field, thus combining the data collection and drafting into a single operation. The area under survey is visible as a whole, which tends to minimum the overlooking of important data. Errors in measurement maybe easily checked by taking check observations on a prominent point whose position has been plotted on the map. If the edge of the blade does not contact the proper point or points, an error is indicated. An error thus located can be easily corrected on the spot. 2. Since all computation and plotting is performed in the field, the keeping of field notes is not a mandatory requirement in plane-table topography; the decision is left up to your supervisor; however, plane-table field notes are useful as a training device. You should keep this in mind when, later in your career, you are training junior EAs in plane-table work. 3. The graphic solutions of the plane table are much quicker than the same solutions by methods requiring angular measurements, linear measurements, and computations. Thus a great deal more area can be covered in much less time. 4. When the country is open and level, the plane-table topographer has a wider choice in the selection of detail points. He need not be hampered by backsight-foresight requirements. He can locate inaccessible points easily by graphic triangulation or quickly determine the location of a point with reference to one, two, or three points of known location. 5. Irregular lines, such as streams, banks, and contours, can be sketched. Figure 9-7.-Progression. 9-6

Privacy Statement
Press Release
Contact