how to draw parallel lines in a farm

[Paul Anilprem]

You have a farm land with an irregular boundary (no shape or symmetry). Within the farm land, you have a compound with a rectangular compound wall. You need to plant a large number of trees in rows of length 100 ft and that are about 80 feet far from the compound wall. The line of trees should be parallel/perpendicular to the compound wall. In the attached image, the dashed green lines are the ones where trees need to be planted.

The only devices that you have access to are a 50ft long measuring tape and a bundle of twine. You can also use white limestone powder for marking. No other tool commonly used by civil engineers is available.


Here is what I am doing -

1. To mark line GH - Tie one end of the twine somewhere between w2 and w4 and stretch it all the way to H. Overlapping the twine with wall w2-s4 will make the line GH parallel to the wall.
2. Use the same approach to mark point F.

Can any one suggest a good way to mark the other points? or suggest a better approach?