Detail plotting by intersection method.
Introduction
Intersection is a method for determining an unknown geographic position (position finding) by measuring angles with respect to known positions. In intersection, the two points with known coordinates are occupied and sightings are taken to the unknown point.
This experiment is useful to study detail plotting by intersection method.
Principle
An unknown point can be established by measuring its direction from two known points.
Equipments Used
- Plane table with tripod.
- Alidade.
- Plump bob.
- Plumbing fork.
- Ranging rods.
- Spirit level tube.
- Drawing sheet.
- Level with tripod.
- Leveling staff.
- Magnetic compass.
- Measuring tape.
- Graticule.
- Clinometer.
- Theodolite.
- Staff.
Dos and Don'ts
Dos
- Center and level the base of plane table accurately.
- Don't forget to orient the plane table with respect to magnetic north.
- Always use good quality drawing sheet for mapping purpose.
- Drawing sheet must be firmly pasted on plane table to avoid any wrinkles.
- Make a diagonal scale and use it for plotting the distances so as to compensate expansion or shrinkage of drawing sheet.
- Bisect the ground object accurately using alidade.
- Measure the long distances with clinometer and clinopole observations, wherever possible.
- This method is accurate than raditaion method but less accurate.
Don'ts
- Don't waste too much of time to carryout exact centering of plane table, particularly in hilly area. It should be set close by within the plotting accuracy limit.
- Ignore plotting the fields having dimensions less than the plotting accuracy.
- Don't use this method in plain and small areas.
Observations
- All the objects in the area are plotted in the same manner.
- The work is completed in continuation of the area.
- Sufficient elevation measurements are taken during work.