How do i determine which numerical degree of ellipse to use when drawing circles in Perspective?

e.g using a 25 degree ellipse template: which element in the drawing do i use to determine that i should use the 25 degree template in the drawing? (ie how i know i should use a 25 degree template instead of lke 15, 30 degrees…etc)

Is there a systematic method to determine it? like maybe when drawing a wheel & using the angle the wheel makes from the viewer in PLAN view to determine how much degrees to use?( esp. in cases where the circle does not lie in front of the viewer’s center of vision)

i’m already past sketching stage, and i know how to calculate the degrees for any ellipse already.

As i didn’t attend formal school, i wish to learn the underlying theoratical relationship between the use ellipse templates & circles in perspective, i’m sure there must be a relationship that manufacturers or professionals use.
Its pretty straightforward for axonometric drawings, but in perspective as there is distortion when its moved away from center & also other factors, i can’t really figure it out. i suspect maybe its calcualte from the PLAN view of a ellipse to viewer?

anyone care to enlighten me on that? i’m really interested to know it and i can’t seem to find the answer anywhere on the net or in perspective drawing books. don’t they teach that at ID schools?

Lightly box out the area where the ellipse needs to go (basically the boundaries of the circle), you may already have some of the information in the sketch (like a ground line or a face where you’re putting the circle detail)

Once you have a cubical face in perspective, find the center of that face, and sketch a line in perspective (going to the vanishing point) through that center. Then Simply place whichever degree ellipse fills the space.

I drew a quick example of what I’m talking about. It started as a cube, then I used that technique to put circle details on each face.

The cylinder is a quick representation of how you should be placing your ellipse on the perspective line.

Hope this helps.

once you do this a few times, you get the hang of just eyeballing it.

thanks for making the time to draw your explanation. Drawing ellipse in planes which are in correct perspective is how i construct them now too.

I’m still very interested to learn the theoratical relationship of the ellipse degrees and circles in perspective. maybe like with reference to plan & elevation views commonly used in Linear persective measurements.

My GF who’s an interior designer used to have to draw perspective views that were derived form plans. It was hugely annoying and tedious and confusing as hell. I teach drawing and and it took me 2 hours of staring the diagrams to figure it out. I would search out interior design drafting books…you probably wont find many people here who know how to do it.

Maybe you’d want to consult with a mathematician specializing in geometry. They might be able to provide some assistance on the theoretical relationships of non-euclidian geometry

If not, and it is indeed a perspective drawing you are trying to create. I don’t know another way to measure the correct degree of opening.

It is possible to accurately measure sections in perspective in any “correct” perspective drawing created though. I forget how to do it (I just eyeball it now, and never actually use vanishing points with rulers), but I have it in my Bound notes from school. I know you need a measuring point, accurate vanishing points, and a station point. You would still be fitting the ellipse inside a lightly drawn “measured” section of the face though…

Remember, an ellipse template is only an approximation. A true circle in perspective will have different curves on all four sides–each curve will “accelerate” towards the vanishing point differently. It’s best to leave that stuff up to software.

Did anyone else learn shadow-projection in school? Tedius as hell…

hey guys, sorry for the late reply! was out of town

@Brett_nyc
i already read many books but none covered the theory of it, almost all of them uses perspective squares & contains it within

@NURb
i suspect ‘Descriptive’ geometry has the answerws , but i can’t find any courses or ppl in my area offering it.

@copyboy
nope. i’m referring to Perspective, not isometric. the tricky thing about perspective is that circles with same tilt changes in degrees when moving away from center of vision. Whereas in axonometric we just measure and the same degrees can be used regardless of distance from center of vision

@cg
ohh… is that so? i used to suspect that too, but some guy in other forums told me that ellipse templates can be used to draw correctly circles in perspective without any modifciation. but he said he forgot how. so i thought posting in a more technical forum like this could shed some light on the matter.

Do a typical perspective drawing of the top of a cube (ie. a square in perspective.) Naturally, you’ll put your vanishing points far away, at the edges of the paper. It should be fairly easy to find an ellipse that fits, touching all four edges of the cube at their centerpoints.

Now do the same drawing, but place the two vanishing points very close together. You’ll get a lot of distortion out of that cube. It’s going to be tougher to find an ellipse that fits correctly, because there is more distortion in the front edge of the ellipse. At this point, you’ll have to cheat, using two different ellipses, one higher angle ellipse for the front edge, and one smaller angle ellipse for the back edge.

You can also try this with photography. To adjust the vanishing points, simply change how close you are to the circle that you’re photographing. Now lay your ellipse templates on the photo and see if they match.

i dont think there can be much of a concrete connection between circles and ellipses when dealing with perspective because an ellipse isnt a circle in perspective its just a good approximation.