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Old 02-20-2019, 04:09 PM
zhm zhm is offline
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Measuring horizontal distance in perspective

Given the room that one knows the ceiling height is 8 foot and the wall length is about 20 feet, can you estimate/calculate the distances from point C to A? How about point C to B?
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Old 02-23-2019, 09:38 AM
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Re: Measuring horizontal distance in perspective

Hi, check out "measuring points in two point perspective". Once placed on the horizon line, and use in conjunction with the ground line, you're off to the races... cheers!
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Old 03-10-2019, 08:33 PM
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Re: Measuring horizontal distance in perspective

Quote:
Originally Posted by zhm
Given the room that one knows the ceiling height is 8 foot and the wall length is about 20 feet, can you estimate/calculate the distances from point C to A? How about point C to B?

Are you asking about calculating the distances from point C to A in the actual scene, or in your drawing/painting? I am going to answer your question based upon my assumption that you wish to determine the distance between C and A in the drawing/painting.

Your answer has rather answered itself, because of the fact that you have already, arbitrarily placed those points in the drawing. Because of this, you truly don't need to perform any sort of calculation to determine their placement--merely measure the distances you have created. But....I don't believe that is truly what you are asking.

However, there is one type of subject for which the principles of linear perspective are seldom explained by art teachers, and that is because they seem to prefer to "wing it", or to "estimate it", rather than relying upon a geometric method of determining it. That type of subject is represented by railroad ties, cracks in a sidewalk, pickets in a picket fence, or grout lines in tile. The obvious "effect" is that as the pickets of a fence recede into the background, they not only become shorter in height, but they also become closer together in their spacing as they recede.

Rather than guessing, or winging it, regarding that progressive spacing, such spacing can be determined by a rather simple, geometric plot.

In the case of your drawing, you will first need to project the converging lines of the floor (left, and right) to the point at which they intersect at the horizon.

Then, you will be able to determine every spacing of horizontal lines on the floor (such as tile, or bricks, or boards) by a geometric method, based upon the simple projection of diagonals through a center line drawn between the two angled, lines of convergence.

I can present this in a more detailed manner, provided you feel that it may be of some help to you in determining the spacing that you desire. . For example, if your goal is to determine a point on the floor that represents the halfway distance in your painting when viewed in full perspective, .....well, this would do it for you, I believe.
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Last edited by WFMartin : 03-10-2019 at 08:39 PM.
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Old 03-11-2019, 11:29 AM
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Re: Measuring horizontal distance in perspective

Here's a great opportunity: Bill offering to work up a tutorial for you, zhm.

I realized just now that my answer should read:
"measuring points in one point perspective" as mistakenly, I'd typed "two" point perspective.

But there's a piece of info missing in your post, you've written about a room with an 8 foot ceiling, 20 feet wide, but how long do you want the room to be? That's critical to implementing the measuring points when drawing in your back wall.

Cheers

Last edited by KolinskyRed : 03-11-2019 at 11:33 AM.
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Old 03-11-2019, 11:48 AM
zhm zhm is offline
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Re: Measuring horizontal distance in perspective

I may not have explained the question very well but I think that you have interpreted my question correctly.

After thinking about your response, I still do not believe that one can find the distance from C to A precisely unless one assumes that the room is a perfect square. If so, then I do believe that one can find these distances very simply using geometry (front, back and sidewalls are 20’ in length therefore the center is 10’ from edges. But if the room is not a square then one still does not have any horizontal distance in the picture to scale from using geometry).

I could turn the question around. If we are viewing the drawing here (not the actual setting), and we measure the real distance from C to A then where on the drawing does one accurately place A?

Thank you for your attention and thoughts! Rick
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Old 03-11-2019, 12:23 PM
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Re: Measuring horizontal distance in perspective

Quote:
Originally Posted by zhm
I may not have explained the question very well but I think that you have interpreted my question correctly.

After thinking about your response, I still do not believe that one can find the distance from C to A precisely unless one assumes that the room is a perfect square. If so, then I do believe that one can find these distances very simply using geometry (front, back and sidewalls are 20’ in length therefore the center is 10’ from edges. But if the room is not a square then one still does not have any horizontal distance in the picture to scale from using geometry).


I could turn the question around. If we are viewing the drawing here (not the actual setting), and we measure the real distance from C to A then where on the drawing does one accurately place A?

Thank you for your attention and thoughts! Rick




Hi Rick,

That is one application of MPs in one point perspective. Draw the width parallel to the picture plane, then draw the converging lines back to the VP. To create a square (L=W) in perspective we use the MPs to show us where to cut those vanishing lines. I think you've done this?

We can also place any distance we like in perspective using the same measuring points. Just count along the groundline/base of the picture plane for the distance we'd like as an off set from the center of vision. Use it like a ruler. Mark that point on the ground line.

From this new point, project/draw it back to the measuring point on the opposite side of the line of sight. Where this new line cuts the convergence line is linear distance we measured out swung around into perspective. (Which converging line are we cutting? The one on the same side as our ground line measuring point.)

Cheers!

Last edited by KolinskyRed : 03-11-2019 at 12:35 PM.
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Old 03-11-2019, 01:56 PM
zhm zhm is offline
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Re: Measuring horizontal distance in perspective

"To create a square (L=W) in perspective we use the MPs to show us where to cut those vanishing lines. I think you've done this?"

If I understand you correctly, I am "creating a square" resulting from the placement of point A. That is, I assume that point A is at a distance of 20' from point C? or perhaps the picture plane is 20' from point C and therefore A must be less than 20'. Of course, I could actually measure the distance from C to A and draw in a rectangle or square, based on the actual (true)measurements. And, if I wished to place additional points in the picture I could use these MPs to do so.

This is an academic exercise to some degree. My question came about while viewing an interior painting done by Daniel Sprick. I began to wonder how large the room is as depicted in the painting.

Thanks, Rick
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Old 03-11-2019, 07:27 PM
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Re: Measuring horizontal distance in perspective

I am going to try to post an attachment of a handout I used to give to my oil painting students who were interested in that aspect of perspective--how to calculate the logical, progressive spacing of parallel lines in perspective.

The primary concern is to be able to create a centerline (which is nothing more than a construction line through which you draw projected lines). From then on, it involves the projecting of diagonal lines up to the top, converging line.

Works like a charm. If you have a drawing of a room of given dimensions in feet, merely make tiles, or boards to represent those dimensions. For example, just create 20 spaces to represent 20 feet, in your room.
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Last edited by WFMartin : 03-11-2019 at 07:32 PM.
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Old 03-12-2019, 12:18 PM
zhm zhm is offline
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Re: Measuring horizontal distance in perspective

Thank you very much! This is a helpful method for properly spacing parallel lines towards a vanishing point!

It seems to me that one should be able to simply determine those distances given the 8'x20' front wall dimensions in the picture and an obvious vanishing point (and without having a known or assumed distance in the z-plane -- using the x, y and z notation from which to scale).

Rick
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Old 03-12-2019, 07:12 PM
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Re: Measuring horizontal distance in perspective

Quote:
Originally Posted by zhm
Thank you very much! This is a helpful method for properly spacing parallel lines towards a vanishing point!

It seems to me that one should be able to simply determine those distances given the 8'x20' front wall dimensions in the picture and an obvious vanishing point (and without having a known or assumed distance in the z-plane -- using the x, y and z notation from which to scale).

Rick

Yes...with the construction of "things" that must maintain a degree of perspective, it is usually the case that the artist (creator of the scene) must first select an initial dimension, or spacing on their own. From that first selection, the remaining elements of perspective can be determined.

I have found that one of the most difficult things to determine whenever I view a rather detailed, or complicated drawing that shows the construction lines, and points, is "What needs to happen first?" In other words, at some point the artist needs to establish SOMETHING upon which all the remaining points of perspective are ultimately based. I have found that very few illustrations of perspective drawing indicate what must be done first.
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Old 03-12-2019, 09:04 PM
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Re: Measuring horizontal distance in perspective

In the case of architecture and buildings, the height is often the first dimension established, i.e., a one-story building is a very different thing compared to a 10 or 30 story building.

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Old 03-13-2019, 10:40 AM
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Re: Measuring horizontal distance in perspective

I'm sure I've misunderstood your question.

For the drawing you've posted this doesn't show the front wall of the room which would be critical to simply cutting it in half/quarters etc using Bill's method along either the side wall or floor. Bill's is a helpful and much-used method in perspective drawing.

But back to your original question. Even if the front wall were showing, and only the height and width of the front wall known, based on your question how to measure to the points you've placed, without knowing the focal length, the distances can't be determined/reverse engineered.

Bill's observation that the artist places by judgement/aesthetic a few elements then uses the basics of perspective drawing to complement the desired elements of a composition is also spot on. So, here the first two verticals are drawn in by eye as to distance apart, as the artist would wish, but doesn't represent any known or inferred distance in your drawing as it's shown. Matching to the VP does show the same foreshortening, though.

But, we can reverse-engineer distances both relative and absolute from a perspective drawing, so long as enough visual information is given. A neat puzzle with which to play.

Was this a sketch of Sprik's painting? Perhaps knowing which one might present us with a clue.

Cheers
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Old 03-13-2019, 10:40 AM
zhm zhm is offline
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Re: Measuring horizontal distance in perspective

Understood and that is what I thought. It is easy enough to see the height of a room which may or may not be standard height if there is such a thing and then one could scale the other dimension in that same plane, i.e. the width of the wall for example. But beyond that and in the case of a dimension in the z axis, apparently it is up to the artist/draftsman to place that first point from which all other points can be scaled to.

So in the case of my sketch, one cannot determine the distance but would be forced to "eyeball" or estimate it. And in the case of composing a picture, the artist establishes that point as he/she sees appropriate.

Great discussion and I thank you!! Rick
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Old 03-13-2019, 11:03 AM
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Re: Measuring horizontal distance in perspective

Thanks to you as well, Rick. Nice puzzle, and I'v learned a new painter, having just looked through Daniel Sprick's paintings. Wow, a true talent. I specially like his landscapes/urban paintings.
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Old 03-14-2019, 11:39 AM
zhm zhm is offline
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Re: Measuring horizontal distance in perspective

Sure thing and thank you for your help!

I believe Dan is one of the best, if not the best, still life painters practicing today--an amazing artist!
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