This video explains about quadrant system required to carry out projections using first angle projection.
A two dimensional space is divided into four parts using two perpendicular lines. These four spaces are known as quadrants. Similarly a three dimensional space is divided into four quadrants using two perpendicular planes. These planes are describes as vertical plane (VP) and horizontal plane (HP). HP and VP intersect forming a straight line called as XY line.
When a point is located x mm above HP and y mm in front of VP, it is placed in first quadrant. The projections of these points is analogous to shadow falling on the screen opposite to an object. When the light falls on the point in horizontal direction, the shadow falls on the plane opposite to it, i.e. VP. This shadow is the projection of the point in Front View (FV). When the light
falls on the point in vertical direction, the shadow falls on the
plane opposite to it, i.e. HP. This shadow is the projection of the
point in TV View (TV).
To obtain the projection we keep the VP in fixed position and rotate HP in clockwise direction. This is done to represent both the projections on a two dimensional sheet.
For first quadrant, the VP is above XY line and HP is below XY line.
When
a point is located x mm above HP and y mm behind VP, it is placed
in second quadrant. The projections of these points is analogous to
shadow falling on the screen opposite to an object. When the light falls
on the point in horizontal direction, the shadow falls on the plane
opposite to it, i.e. VP. This shadow is the projection of the point in
Front View (FV). When the light
falls on the point in vertical direction, the shadow falls on the
plane opposite to it, i.e. HP. This shadow is the projection of the
point in TV View (TV).
To
obtain the projection we keep the VP in fixed position and rotate HP in
clockwise direction. This is done to represent both the projections on a
two dimensional sheet.
For second quadrant, bot HP and VP are above XY line and HP is behind VP. This is denoted as VP(HP).
When
a point is located x mm below HP and y mm behind VP, it is placed
in third quadrant. The projections of these points is analogous to
shadow falling on the screen opposite to an object. When the light falls
on the point in horizontal direction, the shadow falls on the plane
opposite to it, i.e. VP. This shadow is the projection of the point in
Front View (FV). When the light
falls on the point in vertical direction, the shadow falls on the
plane opposite to it, i.e. HP. This shadow is the projection of the
point in TV View (TV).
To
obtain the projection we keep the VP in fixed position and rotate HP in
clockwise direction. This is done to represent both the projections on a
two dimensional sheet.
For third quadrant, the HP is above XY line and VP is below XY line.
When
a point is located x mm below HP and y mm in front of VP, it is placed
in fourth quadrant. The projections of these points is analogous to
shadow falling on the screen opposite to an object. When the light falls
on the point in horizontal direction, the shadow falls on the plane
opposite to it, i.e. VP. This shadow is the projection of the point in
Front View (FV). When the light
falls on the point in vertical direction, the shadow falls on the
plane opposite to it, i.e. HP. This shadow is the projection of the
point in TV View (TV).
To
obtain the projection we keep the VP in fixed position and rotate HP in
clockwise direction. This is done to represent both the projections on a
two dimensional sheet.
For fourth quadrant, bot HP and VP are below XY line and VP is behind HP. This is denoted as HP(VP).