1st Angle vs 3rd Angle projection...

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Was wondering if someone could shed some light on the following.

I know How these two system work so I'm not asking for that..

What I want to know is why would someone take the right side of a house (elevation looking at front door then take the right elevation) and draw it on the LEFT side and think that made sense?  How does that even work with any guide lines?  so I would draw guide lines from the right of the house all the way over to the left of my paper??  and visa versa??

I cannot find the reason for this "car with a steering wheel that to go left you need to turn it right".

what am I not getting? all I can find is videos explaining each system...

Posted (edited)

The answer is in the question.

It depends what you learn. I prefer first angle, especially with the plan view at the bottom of the sheet.

First angle probably developed before the invention of transparent boxes 🙂

1st angle projection

Place the house in a box

The views are projected to perpendicular planes

Unfold & flatten the box

3rd angle projection

Place the house in a box

Look through the box and draw what you see on outside of the box

Unfold & flatten it.

this handy symbol indicates which is being used

Edited by bcd
Posted (edited)

@bcdthanks.  I was trying to avoid someone explaining it to me as I know what it is.

So you would draw the right side of the house (the side that has the chimney)  on the left of your front elevation?

How would you do that manually without drawing guidelines across your front elevation?

Edited by digitalcarbon
Posted (edited)
40 minutes ago, digitalcarbon said:

I was trying to avoid someone explaining it to me as I know what it is.

Yes - I read that but my explanation needed the setup. And others might find it useful.

40 minutes ago, digitalcarbon said:

How would you do that manually without drawing guidelines across your front elevation?

With a T-Square, sometimes they would cross the elevation if you needed to refer to them again, if just picking up once you might just draw them in the side view - but guidelines are just that, and are fine enough that they don't obscure the view.  You don't ink them in.

They would also cross in 3rd angle if you had a different height chimney on the left of the house.

Edited by bcd

the shared corner share dims.

2 minutes ago, digitalcarbon said:

the shared corner share dims.

I'm not familiar with using shared dimensions like that. In your example, unless there was uncertainty the heights could be omitted in the side view.

I think the answer is tracing paper??

Wouldn't you have the same question about guide lines for 3rd angle if the chimney were on the other side of the house?

But more to your point, putting the "right" on the "left" seems pretty unintuitive.

I'm guessing that before the days of digital drafting, it was easier to imagine a viewer on the right side and an object and an opaque plane on the left so the "projection" of the right side ended up on the left. Again, guessing, that in the later days of CAD it became much more common to imagine a transparent plane between the viewer and the object, like a window. And, it makes more sense to most of us that the right view goes on the right. But in the end, it is all about how we train our brains to visualize 3D.

18 minutes ago, BartHays said:

chimney were on the other side of the house

I would draw the left elevation to the left of the front elevation as they have a shared corner

In architecture one would show all elevations.

I have the feeling that for big things a human walks around to the right and left so that is the way they draw.  People mentally "walk" to the corner of the bldg on the paper and there is the elevation only a few inches away.  One would not take their eyes that are focused on a bldg corner and move them to the other side of the paper looking for the adjoining elevation.  The key word is "adjoining".

But for hand held objects they can flip back and for without moving their body.

I cannot believe someone sat down in history and after finishing a front elevation (see above) they then decided to place the right side of a building on the left of the paper (as show in one example above) and then showed friends and family who all said "yea, brilliant! I get it."

Hence, without another rational explanation...and seeing that it needs to be rational (I hope it is) I will assume that it has to do with size of object in relation to the human body & what we hope to find when we take mental walks through our drawings.

6 hours ago, digitalcarbon said:

What I want to know is why would someone take the right side of a house (elevation looking at front door then take the right elevation) and draw it on the LEFT side and think that made sense?

Because different cultures have different ways of looking at the world and developed ways of communicating this.

As long as it is standardized and known, most people do not have difficulty with these concepts.

If you try to force your ways onto situations designed for something else, you will have difficulty... like reading Arabic or Chinese and applying English conventions 🙂

Is this the esoteric answer you seek?

Posted (edited)

@Jeff PrinceThanks Jeff.  it does not really answer the question. so I'll stick with the large objects people walk around and small objects people flip in hand.

I would like to see a culture that actually would draw the house elevation example (show) above in 1st angle...not in todays cad as this is easy.  but actual manual hand drawings.  any pictures from antiquity?

Heard that for the hydrogen bomb design they needed to make full scale drawings.  People walked around on the paper in their socks. Then to see the whole thing they need to view it from balcony.  Heard the same regarding airplane designs back then.

Unfortunately I cannot find any pictures.  I wonder what they did.  I cannot imagine anyone (from any culture) walking across the room to draw on the other side of the paper.  That would be a very long straight edge.

I get metric

I get dividing up a circle into 400 segments vs 360

You can find the history of how things developed on nearly every subject, but not this.

If no one knows that ok.  Just wanted to know.

Edited by digitalcarbon

not really sure what was done here...too small to see unless I buy a print.

Titanic

Chinese,  I think paper constraints had an effect on this.

Arabic,  same as above. paper constraints.

Posted (edited)

it seems like the top view of the boats (Chinese & Arabic) are 1st angle to each other as it is drawn as if the boat was rotated.

Is that correct?

Ok, so now I see where one would use 1st angle. As it would be silly to draw the plan above the sails and not directly under the boat elevation.

Same with the Titanic.  Upon closer inspection (note the blades) is seems that the elevation ends are 3rd angle and the plan is 1st angle.

Edited by digitalcarbon

When I was learning to draft (in 1st angle) 50 years ago we were taught that the "projection lines" issued from the viewer, past (and through) the object and were projected onto the (opaque) "Picture Plane" behind.

Cf 3rd angle where the projection lines land on a "transparent" Picture plane in front. That bit's easy.

As to *why*?....

I suspect the emphasis in mind centred around the primacy of the idea of geometry and projection rather than readability.

Possibly blame Euclid?

13 hours ago, propstuff said:

As to *why*?....

@propstuffThanks,  I was wondering if it boils down to what works as to what is being drawn...the ship examples above have 3rd angle for the elevations and 1st for the plan to the broad side elevation.  I just found a hand sketch of mine where I drew the elevation at the top of the paper (8.5x11) as that was the dominant focus and then drew a partial plan at the bottom of the page.  which turns out to be 1st angle.  If I had wider paper the other elevations would be in 3rd angle to the main.  so I unwittingly worked it out similar to the people who did the boat drawings.

my unwitting 1st angle sketch

This is interesting.  I suppose in some cases there would be a paper constraint, but few.  Making the assumption that everything you see was drawn on the paper you have found is misleading.  For example, the sailboat image was drawn on several pieces of paper and transferred back to one master sheet.  Of that I am pretty sure as the full drawing of the boat is slightly 3D.  It appears you can see the stern.

Also, the views for architecture or mechanical design are what I have always called absolute views, in that they are flat and one dimensional.  Attempting to take the front, side and top views to an accurate 3D view with construction lines is frustrating at best.

Imagine your front elevation as an object on the page.  In first angle, the viewer moves to the right, and draws what they see on the right or unfolds and draws on the right.

In third angle, imagine the object is sitting on your page in elevation view.  If you stay where you are and tip the object to see the right side, you roll the object over its back left corner and the object will end up a little to the left with the right side facing you.  You draw it where it is sitting now.

In first angle the viewer rotates. In third angle the object rotates. I can easily see this as a way a drawing system developed, especially if it started from tracing.

Just because we got trained one way doesn't make the other less valid as long as the draftsperson and the reader have agreed upon the language and the content is conveyed clearly between them.

The concept of Projection, and consequently Projection Lines was also fundamental to Developments and developing True Shapes of plane surfaces.

Likewise, when we were drafting 3 point Perspective views, the central thing to get your head around was the location of the Picture Plane and how points on the Orthogonal views projected on to and intersected on the Picture Plane.

It's all a bit blurry to me now.

It does highlight, though, that the CAD engineers have to be fully intimate with how the mathematics of all this works, *plus*  how the software that they are authoring in can be coded to generate the appropriate result...

paper constraints.

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