Classification Of Triangulation Survey:
classification of triangulation survey:
The triangulation figures of the classification of the basis are determined by the triangulation of a line of length and azimuth with accuracy. Survey of the extent and purpose of the different accuracies of triangulation systems.
The accepted grades of triangulation are:
(1)First order or Primary Triangulation
(2) Şecond order or Secondary Triangulation
(3) Third order or Tertiary triangulation
1). First-order or Primary Triangulation:
The first-order triangle is in the highest order and is used to determine the shape of the earth or to provide the most accurate control points that can connect the second triangle.
The primary triangular system embraces a wide area (usually the entire country). Every precaution is taken in making linear and angular measurements and performing cuts.
The following are the general specification are the general specifications of the primary triangulation :
1.Average triangle closure : Less than a second
2.Maximum triangle closure Length : Not more than 3 seconds
3.Length of baseline : 5 to 15 kilometers
4.length of the sides of triangles : 30 to 150 kilometers
5.Actual error of base : 1 in 300,000
6.probable error of base : 1 in 1,000,000
7.Discrepancy between two measures of a section : 10 mm √kilometers
8.Probable error of computed distance : 1 in 60,000 to 1 in 250,000
9.Probable error in astronomic azimuth : 0.5 seconds
2) Şecond order or Secondary Triangulation:
The secondary triangle consists of several points that are fixed within the framework of the primary triangle. The centers are fixed at close intervals so that the sizes of the triangles formed are smaller than the primary triangles. The tools and methods used do not have the same refinement.
The general specifications of the secondary triangulations are:
- Average triangle closure : 3 sec
- Maximum triangle closure : 8sec
- Length of baseline : 1.5 to 5 km
- Length of sides of triangles : 8 to 65 km
- Actual error of base : 1 in 150,000
- Probable error of base : 1 in 5000,000
- Discrepancy between two measures of a section : 20 mm √kilometers
- Probable error of computed distance : 1 in 20,000 to 1 in 50,000
- Probable error in astronomic azimuth : 2.0 sec
3). Third-Order or Tertiary Triangulation:
The third-order triangle consists of a number of points that are fixed within the framework of the second triangle and form the instant control for detailed engineering and other survey’s.
The sizes of triangles are small and can be used with devices with medium accuracy.
The specifications for a third-order triangulation are as follows :
- Average triangle closure : 6 sec
- Maximum triangle closure : 12 sec
- Length of baseline : 0.5 to 3 km
- Length of sides of triangles : 1.5 to 10 km
- Actual error of base : 1 in 75,000
- Probable error of base : 1 in 250,000
- Discrepancy between two measures of a section : 25 mm √kilometers
- Probable error of computed distance : 1 in 5,000 to 1 in 20,000
- Probable error in astronomic azimuth : 5 sec
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