The radiation method of the Plane table survey is one of the simplest methods of surveying. Unlike its more complex counterparts, the radiation survey method doesn’t require intricate calculations or a plethora of sophisticated equipment. Instead, it relies on a well-established principle – measuring distances and directions – to build a map one feature at a time.
Steps:
- Set up the Plane Table:
- Choose a central location (P) with a clear view of the features you want to map.
- Set up the plane table on a tripod and level it using the levelling head and plumb bob. Ensure the board is horizontal.
- Orient the Plane Table (Optional):
- If you want to show a north arrow on your map, use the drawing compass to orient the long edge of the drawing board in a north-south direction. This step is optional but helpful for overall map clarity.
- Set Up the Alidade:
- Attach the alidade to the plane table, ensuring it moves smoothly along the straightedge.
- Mark the Station Point:
- On the drawing sheet, make a small pinprick or mark a point to represent your current location (instrument setup). This is your station point P.
- Sight and Draw Rays for Features:
- Identify a feature you want to map, a ranging rod is shown in the figure (it can also be a tree, corner of a building, etc.).
- Sight the alidade towards the ranging rod, ensuring the object is centred in the alidade’s sight.
- With the alidade locked in position, draw a line from the station point outwards along the straightedge of the alidade. This line represents the direction from the instrument to the feature.
- Measure and Plot the Distance:
- Walk with the tape measure to the targeted feature.
- Measure the horizontal distance between the station point and the feature.
- Choose a map scale (e.g., 1 cm represents 10 meters).
- Using the measured distance and chosen scale, measure the corresponding length on the alidade’s ruler.
- From the station point on your drawing, carefully mark this scaled distance along the ray you drew earlier. This marks the position of the feature on the map.
- Repeat for Additional Features:
- Repeat steps 5 and 6 for all the features you want to map from this station point.
