How to learn to draw architectural structures: Space and perspective 
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Space and perspective
Space and plans
To image three-dimensional buildings on a flat, two-dimensional surface (paper) requires an understanding of what perspective and space are. When you look at objects, those closer to you seem larger than those that are farther away. To make it easier for you to draw them in perspective, measure with a pencil the relative size of near and distant objects.
The space in which objects are located can be divided into three planes: in the background there will be everything that is far away; in the middle ground, that which is closer to you; in the foreground are the objects closest to you. On paper, you combine these three plans, not forgetting that objects seem smaller and smaller as you move away. This view turns into a fourth plan on a piece of paper, the plane of the picture, on which the near and far objects are next to each other.
Point of view
Your point of view is the position from which you look at the subject. If you are standing at the foot of a building, you cannot see its roof. Once somewhere at the level of its roof, you almost will not see its foundation. Therefore, the point of view plays an important role in choosing the position from which you want to draw the building.
Gaze level
Your gaze level (or eyes) is an imaginary horizontal plane extending from your eyes to the limits of visibility. The horizontal lines of the buildings will seem to go down, to some distant point, if they are above your level of view, or going up if you look at them from above.
Changing your point of view, you will see objects below or above your level of sight.
Linear perspective
Understanding the laws of perspective will allow you to draw compelling three-dimensional objects. The top sketch is a good example of a simple perspective. The receding horizontal lines converge at one point at the level of your gaze. This point is called the vanishing point (1). Vertical structures are also changing. The farther they are, the smaller they seem. In addition, as you move away, the distance between them decreases and they stand closer to each other.
If you come closer to the right columns (2), then the horizontal lines of these columns will converge iodine at sharper angles than the lines of the left row of columns.
Perspective with two vanishing points
If you look at the building and one of its vertical angles is in the center of your field of view, you will see two sides of the building. Horizontal lines will converge on both sides of this central vertical. Here you get two vanishing points - one on each side of the vertical - and both will be at the level of your gaze. If you draw a building from this perspective, you are using a perspective with two vanishing points.
Move vanishing points
The vanishing points will change if you go around the building. On the side where you go, the horizontal lines will converge at a sharper angle, and the vanishing point will move farther away from you. For example, if you go to the left of the central vertical of the Parthenon (above), the left vanishing point will be removed, and the right one will approach (4).
Division of the parties
Any figure that is not parallel to the plane of the picture will be distorted if drawn in perspective. Fortunately, basic geometric shapes show us how to deal with these distortions.
Diagonals drawn from the corners of a square or rectangle intersect in the center of the figure. The vertical and horizontal lines drawn through this center will point us to the middle of each side of the figure. This rule applies even to a rectangle drawn in perspective, with converging top and sides. This geometric property allows you to draw in perspective a series of windows of the same size.
Circles and ellipses
The circle drawn inside the square touches the sides of the square just in their middle. A circle seen in perspective turns into an ellipse, but it will still touch the middle of the sides of the square drawn around it in perspective. Use these contact points of the square when you draw a steep or semicircle in perspective. The resulting ellipse should look as if it lies in the same plane as the square. To get the correct proportions of the square in perspective, use the pencil metering method. Now you are ready to draw in perspective arched windows and doors, arches, round towers and other rounded figures.
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