A lot has been said about drawing linear perspective. However, it seems that little has accually been said or written about finding linear perspective. Proper perspective is crucial for creating a picture that expressly has man made structures within it. It becomes necessary to show proper perspective. Otherwise, the compotition will not be totally correct.
So, how do we go about finding linear perspective? It is really not so hard to do. We just need to be observant. In looking at a scene, we need to observe and determine the directions of the receding horizontal lines.
These lines will be; a building roofline, a row of windows, a fence line, a line of electric poles, a road, a wall, vehicles and so on. Any line or series of objects of similar size that receds into the distance.
In the studio, the job of finding linear perspective is fairly easy. If you have a photo or picture that you are working from, you can use a ruler or straightedge, placing it along these lines. And you can follow and draw these lines back to where they intersect. Anyhow, the vanishing point will be where they intersect. Once you have established the two vanishing points, you will note that the horizon line will flow between these two points.
Linear Perspective Outdoors
Outdoors we have a slightly different situation. Since we do not have a surface to draw on, (other than our canvas), we will have to eyeball the subject matter. Here, you might even consider holding up a straightedge or ruler to help you find the vanishing points. Then, once finding them, fix them into your brain.
This is one of the challenges of plein-air painting. Of course, if you are doing a landscape or seascape with no structures, you will not have to be concerned about linear perspective and vanishing points. Your only concern will be the horizon line and showing aerial perspective.