I could swear I used to do this, but I could also be mistaken.
Is it possible to place a half or quarter ellipse tangent to two lines?
I would suggest possibly using the Tangent Snap may be effective in performing this operation.
Snap Mode Toolbox
RegardsAndrew BellTechnical SupportBentley Systems
Andrew, I am aware of the Tangent snap. It doesn't work for half or quarter ellipses - go ahead and try it.
When I place an arc, I have the option to place it "Start, End, Mid" which allows me to snap tangent to the first line and tangent to the second line. This gives me a dynamic arc that I can "pull" about to get the arc I want. I use this often to create an arc that approximates a line string that looks like an arc, but is a bunch of tiny segments around a corner.
There are no options - none - for placing a quarter or half ellipse. And the snaps don't work in the same way.
The first prompt for a quarter ellipse is "enter one end of the ellipse quarter". Right here, I know I am in trouble. I don't know the specific point for the end of the ellipse. I only know that I want the ellipse tangent to this element over here. I can use the tangent snap if I like, but the point accepted does not save the tangency constraint. It only uses the location, not any tangency.
The next prompt asks "enter point on axis". This is essentially looking for the center point of the ellipse. I don't know that, because i am looking for something more dynamic (like the arc). But I can enter a point, just to move on with the exercise.
The third prompt is "enter endpoint". I do have a semi-dynamic element, fixed at the first point and the "center" I chose. At this point, I can't use the tangent snap. It's not allowed. I have the little "no" symbol over the top of what would be my snap.
I don't use this tool often, and I can see why. I hope I am missing something - some step, some setting, getting the prompts wrong?Perhaps I am remembering the tool wrong and it was never possible to create tangent half/quarter ellipses and I did something else instead...
MaryB
Power GeoPak 08.11.09.918Power InRoads 08.11.09.918OpenRoads Designer 2021 R2
Hi Mary,
It's quite simple to do, you just need to think about the task differently because the tool dictates the task. Tangent Point Snap doesn't work for this task so just stick with Key Point Snap.
To do it:
great but how do you do it to two existing lines?
Lorys
Started msnt work 1990 - Retired Nov 2022 ( oh boy am I old )
But was long time user V8iss10 (8.11.09.919) dabbler CE update 16 (10.16.00.80)
MicroStation user since 1990 Melbourne Australia.click link to PM me
The longer I think about it it seems there's something overlooked. A quarter ellipse needs two lines being rectangular to each other. Therefore there's no need for a second tangent.
I guess you'll need to draw parallel lines to find the center of the ellipse and then go ahead.
But a quarter ellipse could be tangent to two lines with floating endpoints, as in, I know I need an ellipse tangent to two lines, but i may not know what the axis lengths need to be. This means that I don't know the exact points to click. It would also be possible for a quarter ellipse to be tangent to a line, just not at the quadrant.
From time to time, i need to draw fillets with unequal scaling. I work in drawings that may have an exaggerated vertical, like 1H:5V. There are a few ways to place fillets like these, but I thought that placing a quarter ellipse might be a faster option:
I had to draw this quarter ellipse off to the side and move it into place because I can't wrap my head around the calculations to figure out where either endpoint is. Even now, I'm not certain if the ellipse is actually tangent to the slanted line because I have problems getting "Move to Contact" to work the way I expect, but that's another discussion for another time.
It's OK if this can't be done with the tools as they are. As I said, I have other ways of constructing what I need.
hi Mary , no mstn avail here anymore being retired and Bentley Being extremally stingy about probono home licenses, but from memory under fillet we had circular right but wasnt there another option? I thought it was elliptical... Geometry was 100 years ago at high school so whats special about a quarter ellipse anyway
An issue which I recognise with what you have told us is that there simply isn’t enough information to place such an ellipse accurately .
MaryB said:I work in drawings that may have an exaggerated vertical, like 1H:5V
Is that a ratio or linear values for the Semi-Major and Semi-Minor axises (presumably in feet)?
Additionally, can you confirm how the Major axis aligns in relation to either of the lines in your previous image? I think I am correct in the assertion that there are infinite combinations for the tangential points of contact between the lines and the partial ellipse so you need to reduce the Degrees of Flexibility by confirming what it should be e.g. should the major axis be perpendicular or parallel to one of the lines? This isn’t required with a fillet as its radius is constant, whereas you will appreciate that with your ellipse, it’s variable.
MaryB said:because I have problems getting "Move to Contact" to work the way I expect
Yes, that tool is imperfect, and recently forced me to write a VBA program for the case between circle and ellipse with a given vector, it requires a complex calculation:
en.m.wikipedia.org/.../Quartic_equation
Therefore, that kind of process cannot easily be completed by basic drawing tool.