Linear Perspective is the most basic form of perspective in which all objects with faces parallel to the horizon, appear to converge in the distance at a single point on the horizon (the vanishing point).
To learn what on Earth this possibly means, grab yourself:
- a few sheets of 18" x 24" paper
- a pencil
- a straight metal ruler
- a white mars plastic eraser
and dare follow me to the next step.
Step 1: Vanishing horizons.
Now, if you were to stare straight ahead at the horizon, the point on the horizon directly in front of you would be considered the vanishing point. It's called the vanishing point since all objects seem to vanish towards it as they go back into the distance.
Step 2: A single point. A single perspective.
In other words, if there was a cube between you and the horizon, the face of the cube closest to you would have two horizontal lines parallel to the horizon. In fact, everything viewed in this perspective must have horizontal lines parallel to the horizon.
If horizontal lines are no longer parallel, you have just gained a whole new perspective (but lets not worry about that for now).
Step 3: Your turn.
Next, you want to find the midpoint on the sheet of paper.
The easiest way to find the midpoint is to connect each opposite corner on the sheet of paper. Where the two lines converge is the center point (the center point of any parallelogram - rectangle, square - can be found this way).
Your center point should fall right in the center of the line you have just drawn. Enlarge this point and label it V.P. for vanishing point.
Erase the diagonal lines, but leave the horizontal line since that is now your horizon.
You should be now left with a horizon with a vanishing point centered on it.
The vanishing point must always be located on the horizon!
Step 4: L7 Square
Connect each set of points with a vertical line so that you have two vertical parallel lines.
Now measure 1" up from the horizon and make a mark on both lines and then measure 1" down from the horizon line and do the same.
Connect both new sets of dots to form a square.
Step 5: The Thirrrrrd Diiiimension!
And of course, anything with depth must appear to travel back towards the vanishing point.
To give your box depth trace the top and bottom right-edges back towards the vanishing point (where they should converge).
You now have a mighty long box. You're probably going to want a box that looks a little more reasonable.
On one the lines you just drew, pick a point that is about half-way between the original square and the vanishing point. Make a small mark and measure how far it is from the left edge of the paper.
Once you know the distance, move your ruler vertically up or down from this point and make another dot.
Connect these two dots and extend the vertical line to fully intersects diagonal lines that you have just drawn.
You should be left with something that resembles a three-dimensional box. Erase all lines until you are left with just a box sitting on the horizon (with a vanishing point).
Step 6: In good company
One rectangle should be above the horizon line (to the right or left of the vanashing point). One rectangle should be below the horizon line (to the right or left of the vanashing point). The third rectangle should be above or below the horizon and positioned so that it is also above or below the vanishing point. The last rectangle should be on the horizon line, but on the opposite side of the vanishing point as the first box. Don't allow any of the rectangles to intersect.
Step 7: A perspective on boxing
Starting with the rectangle above both the horizon and vanishing point, draw a horizontal line connecting the diagonal lines. This should complete the box. Erase all unnecessary lines.
Next find the rectangle that is also above the horizon (but not above the vanishing point). Draw a horizontal line between the diagonals projecting from the bottom two corners and the vanishing point. At the point where the right diagonal line meets the newly created horizontal line, draw a vertical that connects to the diagonal that has been drawn from the top corner of the square. You should now have something that looks like a box. Erase all excess lines until you have a clean box.
Now, with the rectangle below the horizon, you are going to do similarly. Create a horizontal connecting the diagonals coming off the top corners and then drop a vertical from this intersection to the line drawn from the bottom corner.
The rectangle on the right should be completed in a similar manner to the one shown in "Step 5"
You should now have 4 new three-dimensional boxes.
Step 8: Demystifying the horizon
From the image below we can now assert a couple of things.
1) All boxes at least have one visible face. This is the closest rectangular face to you, the viewer, and it is parallel to to the horizon line.
2) Any box sitting on the horizon line and is located to the left or right of the vanishing point will have 1 additional visible face that fades into the distance. This additional face is a side-ace. (visible faces in total: 2 - a front face and a side face)
3) Any box sitting above the horizon line and is located to the left or right of the vanishing point will have 2 additional visible faces that fade into the distance. These additional faces are a side-face and a bottom-face. (visible faces in total: 3 - a front face, a side face and a bottom face)
4) Any box sitting below the horizon line and is located to the left or right of the vanishing point will have 2 additional visible faces that fade into the distance. These additional faces are a side-face and a top-face. (visible faces in total: 3 - a front face, a side face and a top face)
5) Any box sitting in front of the vanishing point will only have one visible face. You will be unable to see the top, bottom, left or right-faces since all vanishing lines are hidden from view. (visible faces in total: 1 - a front face)
6) Any box sitting directly above the vanishing point (and horizon) will have 1 additional visible faces that fade into the distance. This additional face is a bottom-face. (visible faces in total: 2 - a front face and a bottom face)
7) Any box sitting directly below the vanishing point (and horizon) will have 1 additional visible faces that fade into the distance. This additional face is a top-face. (visible faces in total: 2 - a front face and a top face)
In strict one-point perspective, no solid object can be drawn and/or viewed outside the parameters just listed.
Using these guidelines, you can accurately (re)present any forward facing three-dimensional object that you may find in life.