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 This topic has 8 replies, 5 voices, and was last updated 1 year, 5 months ago by Gribbey.

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May 7, 2023 at 12:55 pm #1512557
I’d really appreciate help with this.
There are two vanishing points, A and B, on the horizon line, for two parallel vertical planes to the right of the viewer.
The crossed lines at points C And D are mapping horizontal planes, top and bottom of the cuboid, on a vertical (line not shown).
All good, right?This doesn’t look anything like linear perspective rules, does it? How?
Sorry, I can’t seem to make this question clearer. I’ve been drawing all day…. and not really proving anything. I thought there was supposed to be one vanishing point for such a figure.
C&C welcome
"If you go out in the woods today, you're in for a big surprise!" Jimmy KennedyMay 7, 2023 at 1:13 pm #1512559So did I.. why have you got two?
May 8, 2023 at 2:55 am #1512617There should be only one vanishing point.
Check out the 101 drawing thread on Perspectives.
Doug
We must leave our mark on this worldMay 9, 2023 at 4:12 am #1512780According to those confounded (and confounding) rules, there should be only one VP. But then, as we discussed before (I think, without checking back), perspective is convention; it’s not ‘real’.
So, judged by those perspective rules your drawing is ‘wrong’. However, ignoring the rules and those perspective lines, the drawing looks ok. Yes, we would be seeing more of the inside of the shape than ‘true’ perspective would allow, but so what? Many artists ignored those rules very successfully to make paintings that are far more interesting than drawing to a grid of perspective lines. That’s why I find those Cannaletto et al paintings to be astounding for the control and application of technique, but oh so dull as an exciting painting.
That’s my twopenneth anyway.
PLEASE how do I make these dreadful yellow things go away? OMG there's even more of the awful things now.
www.instagram.com/john_humber_artist
www.instagram.com/john_petty_letterformMay 12, 2023 at 1:14 pm #1513112So, hmm, thanks, everybody.
I think I’m using a system but I don’t know what it is.In one regard it’s like my ‘circle for reference’ that I’ve mentioned recently in other posts. I am plotting here both horizontally and vertically like in the circle.
I’ve wandered into 3D geometry where DesarguesPascal’s planes in space meet and triangles in perspective project straight lines. Maybe.
I’m wading around in the mud! And not getting the notifications that anyone has responded, sorry! at least not yet
C&C welcome
"If you go out in the woods today, you're in for a big surprise!" Jimmy KennedyMay 15, 2023 at 1:40 pm #1513416I kept working on it. I thought of finding out if the two triangles ending at the vertices C and D in the first diagram above, and which triangles make the top and bottom of the cuboid are ‘in perspective’. Guess what! they are. (not all triangles are in perspective)
Taking into consideration that my sketches are free hand, and that I’ve transposed them upsidedown and backwards, without matching labels, I hope that they make sense to someone else (besides me)!
Attachments:
You must be logged in to view attached files.C&C welcome
"If you go out in the woods today, you're in for a big surprise!" Jimmy KennedyMay 15, 2023 at 1:47 pm #1513419So, here’s a pretty nice link to Desargue’s theorem :
https://www.geogebra.org/m/DQQDuQAz
C&C welcome
"If you go out in the woods today, you're in for a big surprise!" Jimmy KennedyMay 27, 2023 at 12:21 pm #1514710I’m not sure what you are intending to do.
In your first drawing, if the object is box shaped then there would be only one vanishing point on the horizon.
For the object to have two separate vanishing points on the horizon, either the vertical left side, or the vertical right side, should be at an angle to the other.
May 28, 2023 at 7:02 am #1514775Hi Keith, Short version of my intention is to apply principles of 3D geometry to a diagram of a real life scene.
My original objective was to get better at depicting reallife spaces at close range, like interiors or my back yard garden. I found I’d be confused trying to apply linear perspective so eventually I happened on this device, a conceptual tool, I call ‘a circle for reference’. It works really well for me and has become shorthand, something I refer to in the course of direct drawing or painting. I used it in the painting of the bed above (and which is posted here showing the circle if you scroll down: https://www.wetcanvas.com/forums/topic/timeinacorner/
I have been advised (Canadian copyright office) to not post the whole essay explaining my tool online, which leaves me to talk around and about it. I’m doing this here on wet canvas to hear myself think and hopefully be exposed to helpful criticism. Maybe I’ll be ready to write part two of the essay showing why it works… in terms of 3 dimensional geometry and other things.
So, working backwards from the painting results, I have this diagram , another version than the one above showing the construction of the room as the ‘box’ :
And I noticed, in the course of this posting, there are two triangles that are ‘triangles in perspective’ (in green) which means that from one viewpoint, a point, you can draw straight lines from that point through the three respective apexes of the two triangles a (to a1) b( to b1) and c (to c1) . Proof they are in perspective. (Desargues)
I didn’t expect that. I got to that conclusion another way though, Pascal’s Theorem:
So, there are a couple of 3D principles that I think about. 1) any two planes that are not parallel will meet when extended making a straight line. 2) two triangles in perspective will, when their respective three sides are extended to three crossing points, show a straight line running through those three crossing points.
The triangles in my original diagram (with the multiple vanishing points) works to make that straight line from the green triangles’ three crossing points ( the diagram on brown paper above) and the painting was the source of the first diagram in the posting (and the painting was based on the ‘circle for reference’).
It may be just really obvious to a mathematician or maybe it’s just completely bogus! as applied to art. Or like the conceptual tool linear perspective, just another (new and simple despite the explanation:)) tool.
Please feel free to disprove this or make it better. Any thoughts appreciated. Thank you!
C&C welcome
"If you go out in the woods today, you're in for a big surprise!" Jimmy Kennedy 
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