Surveying (General Engineering) (SSC JE)

Horizontal circular curve
Deflection angle– A deflection angle is the angle which a survey line makes with the prolongation of the preceding line.
Back tangent–The tangent line before the beginning of
the curve is called the back tangent or the rear tangent. The line AT1 is the back tangent.
Forward tangent–The tangent line after the end of the curve is called the forward tangent. The line T2B is the forward tangent.

The stadia diaphragm has three horizontal hairs.
• Stadia diaphragm is used in tacheometric surveying.

• In a longitudinal glacier the bergschrund is at the top end of the glacier at a right angle to the flow of the glacier.
• It is caused by the downwards flow of the glacier.
• In winter, a bergschrund is often filled by snow from avalanches from the mountain above it.

Plane table board–The drawing board is carefully made of well-seasoned wood so that counteract the effect of warping the damages due to weathering.

• The size of plane table is 600 mm × 500 mm, 750 mm × 600 mm or 1000 mm × 750 mm, having thickness 15- 20 mm.

The following types of method are used in contouring–
1. Tachometric method of contouring
• In this method is used for angular surveying.
• Its method is best suited for hilly terrains.

2. Direct method
• This method is accurate but very tedious and slow.

3. Square method or grid method
• It is generally used in plain terrain.

4. Cross-section method
• It is generally used for hilly terrain to produce contour lines.

Hydrographic surveys–
• These surveys are conducted on or near the water body, such as lakes, rivers, bays, harbours.
• Marine surveys are special type of hydrographic surveys, covers a broader area near sea for offshore structures, navigations, tides etc.

Level line–A level line is a line laying in a level surface. It is there force normal to the plumb line at all points.

Horizontal line–It is straight line tangential to the level line at a point. It is also perpendicular to the plumb line.

Multiplying constant (k) = f/i
Additive constant (c) = f + d
where,
f = focal length
i = stadia hair interval
d = distance between the optical center of the object lens
Note–For anallatic lens instrument have additive constant zero and multiplying constant (100).