The method of drawing a straight view is called oblique drawing. In the process of drawing, the length of the straight line parallel to the X axis remains unchanged under direct vision, and the length of the straight line parallel to the Y axis becomes half of the original. And the angle with the original axis becomes 45 degrees.

For a triangle, the base is constant, the height becomes 1/2, and then it becomes √2/4 when it is tilted by 45 degrees.

According to the area formula of triangle, the area ratio of original view and direct view is √2/4.

Extended data:

Diagonal mapping rules:

1. Take the X axis and Y axis which are perpendicular to each other in the known image, and they intersect at point O. When drawing a vertical view, draw the corresponding X ′ axis and Y ′ axis, which intersect at O ′, so that ∠ X ′ O ′ Y ′ = 45 or 135, and the plane they determine represents the horizontal plane.

2. Given the line segments parallel to X axis or Y axis in the drawing, draw the line segments parallel to X ′ axis and Y ′ axis in the orthographic drawing respectively.

3. The length of the line segment parallel to the X axis in the known graph remains unchanged in the orthographic view, and the length of the line segment parallel to the Y axis becomes half of the original length.

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