To run a straight line between two points, when both ends are inter visible, we establish intermediate points through line of sight.

Explanation:
When we need to establish a straight line between two points that are inter visible, it means that we can see one point from the other point without any obstacles or obstructions in the line of sight. To ensure accuracy and precision in establishing this straight line, we use the concept of line of sight.

Line of Sight:
Line of sight refers to the imaginary straight line that can be seen from one point to another without any obstructions. It is the path along which the human eye can see clearly. In surveying and civil engineering, line of sight is an important concept for establishing accurate measurements and alignments.

Procedure:
To establish intermediate points between two inter visible points, we follow the process given below:

1. Select the two inter visible points: Identify the two points between which you want to establish the straight line. Ensure that there are no obstacles blocking the line of sight between these points.

2. Set up the instrument: Use a surveying instrument such as a theodolite or a total station to set up at one of the points. Ensure that the instrument is leveled properly and aligned with a reference point.

3. Take a back sight: Look through the instrument and align it with a reference point, such as a benchmark or a previously established point. This is known as taking a back sight.

4. Observe the line of sight: Look through the instrument towards the other inter visible point. Ensure that there are no obstacles or obstructions in the line of sight. Adjust the instrument if necessary to align it accurately with the desired point.

5. Establish intermediate points: Based on the line of sight, select intermediate points along the desired straight line. These points can be marked on the ground or recorded in a surveying notebook.

6. Repeat the process: Move the instrument to the next intermediate point and repeat steps 3 to 5 to establish additional intermediate points until reaching the final destination.

By following this procedure of establishing intermediate points through line of sight, we can ensure a straight line alignment between two inter visible points in surveying and civil engineering. This technique helps in achieving accurate measurements and alignments for various engineering projects.