Descriptive geometry . Fig. 71. Fig. 72 TRUE LENGTH OF A LINE 27 is a^a^ or the distance from a^ to GL. Construction. Fig. 70. The point a isrepresented by its two projections, a and a^.Through a!^ draw HX perpendicular to D^.The revolved position, a! or d\ will lie in HXat a distance from D^ equal to the hypotenuseof a right triangle, one leg of which is the dis-tance from a^ to the axis i>^ and the other legis the distance from ay to GL. If the axis lies in Fi the revolved positionof the point will lie in a line passing throughthe vertical projection of the point perpen-dicular to the axi
Descriptive geometry . Fig. 71. Fig. 72 TRUE LENGTH OF A LINE 27 is a^a^ or the distance from a^ to GL. Construction. Fig. 70. The point a isrepresented by its two projections, a and a^.Through a!^ draw HX perpendicular to D^.The revolved position, a! or d\ will lie in HXat a distance from D^ equal to the hypotenuseof a right triangle, one leg of which is the dis-tance from a^ to the axis i>^ and the other legis the distance from ay to GL. If the axis lies in Fi the revolved positionof the point will lie in a line passing throughthe vertical projection of the point perpen-dicular to the axis and at a distance from thisaxis equal to the hypotenuse of a right tri-angle, one leg of which is the distance fromthe vertical projection of the point to the axis,while the other leg is the distance from thehorizontal projection of the point to the groundline. 39. To determine the true length of a line. Principle. A line is seen in its true lengthon that coordinate plane to which it is parallel,or in which it lies (Figs. 16
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