# Why do we use 1st and 3rd angle projection?

## Why do we use 1st and 3rd angle projection?

We consider that horizontal plane rotates in clockwise direction after having projection on it. that’s why we use 1st angle and 3rd angle projection. because only in this two quadrants we will get the both views after clockwise rotation of horizontal plane.

## What is a 3rd angle projection?

3rd Angle project is where the 3D object is seen to be in the 3rd quadrant. It is positioned below and behind the viewing planes, the planes are transparent, and each view is pulled onto the plane closest to it. The front plane of projection is seen to be between the observer and the object.

What is a first and third angle drawing?

The difference between first and third angle projection is in the position of the plan, front and side views. In third angle, what you see from the right would be drawn on the right. In first angle, the view from the right would be projected through and drawn on the left.

What is a first angle projection?

First-angle projection: In this type of projection, the object is imagined to be in the first quadrant. Because the observer normally looks from the right side of the quadrant to obtain the front view, the objects will come in between the observer and the plane of projection.

### Who uses 1st angle projection?

First angle projection is widely used throughout all parts of Europe and often called European projection. Third angle is the system used in North America and alternatively described as American projection.

### Why do we use 2nd and 4th angle projection?

Overlapping projection views create confusion in the drawing. Therefore the 2nd angle projection system is not used to draw engineering drawings. Therefore fourth angle projection is also not used. To sum up, Because of the overlapping of front and top views 2nd and 4th angle projections are not used.

What is 2nd angle projection?

In Second quadrant, Vertical plane (VP) lies in between object and observer. Therefore front view of the object will lie on vertical plane whereas top view will lie on horizontal plane. As per rule of projection when horizontal plane is rotated 90 degree in clockwise direction, top and front view will overlap.

Which projection is used in India?

polyconic projection
In India, the polyconic projection is commonly used by Survey of India (SOI). All SOI toposheets are in the polyconic projection. Map Scale is the ratio of distances on map to distances to on the surface of the earth. It is specified in verbal, numeric or graphical form on all standard maps.

## What is RF in engineering drawing?

Explanation: Representative fraction is the ratio of the length of the object represented on drawing to the actual length of the object represented. So the representative factor is that dimension in drawing to actual dimension. R.F.

## What do you mean by HT and VT of a line and a plane?

• Horizontal Trace (HT) The real or imaginary line of intersection of a plane. with the HP is called horizontal trace of the plane. HT is always located in the TV. • Vertical Trace (VT) The real or imaginary line of intersection of a plane with. the VP is called vertical trace of the plane.

What are the types of projection?

There are two main types of projection:

• A. Parallel and Orthographic.
• Station-point and Perspective.
• Parallel and Convergent.
• Perspective and Parallel.