|
D E S C R I P T I O N of a L I N E :
- a line is a geometrical shape which has only length dimention .
- the length of a line is infinite . In each description we get only a part of this infinite line - this part is called a segment .
- a segment is part of an infinite line limited on its both ends.
- any line can be described on a projection plane by orthogenic projection .
- a straight line can be parallel to the prijection plane , perpendicular to it , or inclined to it .
- it is sufficient to locate two points of a straight line - in order to draw all its views .
- the view of a line is the line created by the meeting our projection plane with the plane which passes
through the line - perpendicularto the projection plane .
TRACES of a straight LINE :
- a straight line which is not parallel to the projection plane - meets the plane at some point ,
this point is called the line's trace .
- the line's trace where the line meets π1 is marked
by the letter H .
- the line's trace where the line meets π2 is marked
by the letter V .
- the line's trace where the line meets π3 is marked
by the letter F .
the TRUE LENTH of a SEGMENT of a LINE :
- the views of a segment of a line which is in a slanted position towards all the picture-plnes will all be seen shortened - and the views will not
show the right size of the segment .
- asegment which appears as a point in one of the projection planes is in reality a segment which is perpendicular to that plane - and parallel to
all other adjacant planes - and is seen at its true length on them .
FINDING the TRUE LENGTH of a SEGMENT of a line :
:
METHOD no. 1 :
Iin this method it is possible to find the true length of a slanted segment by introducing another projection plane which will comply to two demands :
- a : the new plane must be parallel to a view of the segment on any projection plane .
- b : the new projection plane must be perpendicular to the view's plane
.
METHOD no. 2 :
it is also possible to turn the slanted segment until it gets to a situation in which it is parallel to one of the projection lines - in this situation the
segment's true length will appear on the adjacant plane .
|
