View Full Version : Measuring Accurate Proportins in a perspective drawing

01 January 2005, 09:46 AM
:) Hi! I would like to know how i could accurately measure proportions from a perspective drawing ? or how could i convert a perspective drawing into an orthographic drawing with accurate proportions ? I hope i have accurately framed this question and asked it in the right forum.I would greatly appreciate your comments.Thank you very much in advance.:)

01 January 2005, 02:39 AM
In my theorising I've found 2 problems with perspective drawing currentday.

One is parallax, the actual effect with perception is that all straight lines are bent occurring to function which I willingly did not persue to calculate. I suspect it is something of a parallel to lens curvature and sensor region of image building/sampling. This effect can be best seen in wideangle lens photography. In todays drawings perspective is represented through drawing lines onto a vanishing point. It's a good fast solution and I don't mean one should not do that.

Second; :bounce: human error and nature. there's a looseness often in drawing which differ per artist. I find myself misinterpreting them often. Consequently I find myself asking for instance, why did he make it hollow instead of protruding like he drew it. This could easily happen to a perceiver that's not the artist him-/herself, and even to the artist himself applying techniques to approximate and suggest form instead of produce the exact requirement. this effect will be robably not so evident in photorealistic paintings and such, obviously.

And in answer to your question, I suggest finding the vanishing points for corresponding objects drawn. Assingning one of them a scale, let's say 1,70 m=object=1. now from the extents that define the 1,70 m you draw towards the perspective vanishing points. you measure the deviation from that value in scale:(1=1,70m=objectA)*(1-deviation concluded) taking this and multiplying 1,70 with the outcome= true length. If the 2 objects are not parallel this is complicated to do but you can use the phythagoras system, I think, to interpolate. Since the perspective is inherently wrong, you are measuring an illusion. This is something best done by the human brain, lol:). Check my 3d wip, as soon as I tested the eye curves for an actual eyeball geometry the flaw in the drawing came out; lol, she was apparently running 200 km/h and suddenly stopped when I took the picture.

01 January 2005, 01:38 PM
:) Thank you so much jmBoekestein for your detailed explanation to my question.It certainly clarified my doubts.:) Your 3d wip looks great . I loved the concept art and the modelling is fabulous, its going to look amazing when you are done .:thumbsup: :applause:

01 January 2005, 07:01 PM
Thanks Sanskrit,

I'm very glad you like it!:D Hope to see some of your work soon.

Good luck.

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01 January 2006, 10:00 AM
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