CAD CAM EDM DRO - Yahoo Group Archive

Rhino......

on 2001-03-22 12:39:27 UTC
"was drawings from overseas (Europe) where the projections were in
reverse of the way it's done in the US. This takes a lot of though
sometimes to figure out what the person drew when a compound angle
sectional projection is drawn "upside down and/or backwards" (to us)."

Good morning Smoke and others,

I fully realise that you plus others on the list are very well versed
with orthogonal projections, isometric, etc.

and backed by a great wealth of practical experience, for which I
have great respect. I have found that what

confuses many people are the different ways in which people on the
different side of the big pond arrange the

views, meaning third angle projection in the States and first angle
(still???) in UK and Europe, etc. (hoping to

get some response from that part of the world)

I am trying to prepare some graphics to illustrate the difference.

In the classic explanation of "multiview" readers are asked to
imagine an object in the middle of a box and imagine

projecting the views onto the sides of the box. To illustrate, we
need to see the object through the sides of the

box. In the illustrations below, the box is not transparent, so you
will have to visualise in your mind the object

below in the middle of the box

____
/ /|
/___/ |___
| | / /|
| |/__ / |
| | /
|______|/


Third angle: (see how much easier to understant if we could see
through the box at the object in the middle)
____________
/ _______ /|
/ / / / / |
/ /__/___/ / |
/___________/ /||
| ___ | / ||
| | |___ | |/||
| | | | |//
| |_____| | /
|__________| /

Now we have to imagine a video unfolding as the "panes" are rotated
about the hinge, resulting in:

___________
| _______ |
| | | | |
| |__|___| |
|___________|_________
| ___ | ____ |
| | |___ | |___| |
| | | | | | |
| |______| | |___| |
|___________|________|

In first angle, the views are placed at the opposite end of the
object from where they are viewed, example, what we

see from the top is placed at the bottom:
___________
/| ___ |
/ | | |___ |
/ |_|__ | |
//| / /|___| |
// |/___/ |___ |
||/|| | / /|__|
|| || |/__ / | /
||/ | | / /
| /|______|///
| / /__/___//
|/__________/

Unfolding the views results in the arrangement below,

_______ ___________
| ____ | ___ |
| |___| | | |___ |
| | | | | | |
| |___| | |______| |
|_______|___________|
| _______ |
| | | | |
| |__|___| |
|___________|

where the respective views are placed at the side OPPOSITE from the
side where they were viewed!!! (is this a

conspiracy by the ex-colonial powers to confuse us poor natives?).
For example, the view from the top is placed

below the front and the view from the right is placed to the left of
the front. They still teach first and third

angle projections in the schools, and I think the poor overloaded
education dept and/or teachers have resorted to

teaching projections by rote, meaning just do what I say, which is,
draw:

Third angle: plan on the top, front view at the bottom, side view on
the right
First angle: plan at the bottom, front view at the top, side view on
the left.

and students missed the basic principle, which is
Third angle: view placed on the same side from where they are viewed
First angle: view placed on the opposite side from where they are
viewed

Any variation from the standard arrangement and they start scratching
their heads.

Any graphic and animation experts out there who will like to help
clear the confusions.

Peter

Discussion Thread

Peter Chen 2001-03-21 03:13:12 UTC Rhino...... Smoke 2001-03-21 20:39:55 UTC Re: [CAD_CAM_EDM_DRO] Rhino...... cadcamcenter@y... 2001-03-22 12:39:27 UTC Rhino...... Smoke 2001-03-22 13:51:40 UTC Re: [CAD_CAM_EDM_DRO] Rhino......