The image of a subject on the drawing has to give complete idea of its form and design features and can be executed by means of rectangular projection, linear prospect and an axonometrical projection.
Instruction
1. Remember that the dimetriya is one of types of an axonometrical projection of a subject at which the image is strictly tied to the natural system of coordinates Oxyz. Dimetriya is characterized by the fact that two coefficients of distortion on axes are among themselves equal and other than the third. Dimetriya is rectangular and frontal.
2. At a rectangular dimetriya axis z is located vertically, the axis x forms with a horizontal line a corner 7011', and y corner – 410 25'. The provided distortion coefficient on an axis at is applied by ky = 0.5 (real 0.47), kx = kz = 1 (real 0.94). GOST 2.317-69 recommends to use only the provided coefficients at creation of images in a rectangular dimetric projection.
3. At a frontal dimetric projection the distortion coefficient on an axis at is equal 0.5, and on axes x and z is equal to 1. The axis tilt angle at can be 300 and 450.
4. To draw a rectangular dimetric projection, note a vertical axis of Oz on the drawing. For creation of an axis x represent on the drawing a rectangle with legs of 1 and 8 units which top is O. Gipotenuz's point of a rectangle will become an axis x which deviates from the horizon on a corner 7011'. For creation of an axis at also represent a rectangular triangle with top in O. Velichin's point of legs in this case of 7 and 8 units. The received hypotenuse will be the axis at deviating the horizon on a corner 410 25'.
5. Consistently measure sizes of visible lines of a subject and you transfer them to the drawing, without forgetting to multiply length of the line located on an axis at by the distorting coefficient 0.5.
6. At creation of a dimetric projection the size of a subject turns out increased by 1.06 times. At the same time the image of a circle are projected in an ellipse in the coordinate planes of Howe and uo with the bigger axis equal 1.06d where d is diameter of the projected circle. The small axis of an ellipse is equal to 0.35 d.