Hi,
V5
I have a curve of points I wish to best fit a gentle very shallow arcing curve through, but it must start on the first point and end on the last point.

Q1) How is this done ?

I have used ControlPointCurve tool and drawn snapping to each point but I want to get the subtle wriggles out of this now. ( I could also have used right click on that tool and curve through points)

Q2) Also if with that shallow arcing curve drawn as such, I wish to alter its shape a little still keeping it arcing and gentle and smooth, and again it must start and end on the points, how is this done ?

F10 and pulling on the controls loses the smooth sweep, one is attacking parts of the curve without regard to its overall curve.

If I had drawn it in Freehand with its curve tools I could simply pull out the handle for the start of the curve and the whole curve would adjust.

The handles curve tool does not see the same handles show up when one edits a curve. (separate post on this discovery somewhere)

Q3) I also sometimes need to draw a best fit curve through points starting and ending tangent but the only curve tool I know that has start tangent doesnt do best fit. InterpCrv

If youâre just trying to smooth the curve out a bit, you might try using Rebuild and playing with the number of points, watching the deviation and the on-screen display - keep the points to the minimum you can. Under Rebuild, the end points do not move.

Otherwise there are also the commands Smooth and Fair, to be used in conjunction with CurvetureGraph, perhaps. End points also stay in place with those.

I am in top view, Y is the direction it needs smoothing in, trying 0.5 Smooth causes both ends of curve to kick out and curvature graph starts off looking fair and showing a shallow S and I need a shallow arc. then using smooth 0.5 and graph looks a lot worse.

Rebuild wouldnt lose the S curve nature and give me the shallow arc.

try fair, started with default tol 10. no good, though graph stays flowing, but indicates an S curve.

Now having tried 20 then undo then 50 then undoâŚetc on 300 and still an S curve. Will it in time lose the S, its shallow but there., or is Fair never going to do that ?

The answer I think lies in Q1âŚstill wondering though on Q1) How does one draw an arcing curve through points as opposed to the S or multiple S curves that Control Point Curve gives ?

also Q3)

and Q4 an additonal question, why isnt there an arc best fit through points command ?

I have spent hours trying to draw arcs through points, just realised thats what I need, MORE ACCURATELY THOUGHâŚ my arcs are not a constant radius, so a way of drawing curve through points but constraining the curve to an âarchingâ type curve , as opposed to an S type curveâŚC type not S type !

If you need a shallow âarcâ why not Rebuild the curve with degree 2 and 3 points, then in Top view use the middle control point to adjust the arc as you likeâŚ

In NURBS you must have a minimum of degree+1 points for any given curve; exactly degree+1 points makes a single âspanâ. More points than degree+1 will create a multi-span curve.

If you have a degree 2 curve with 3 points it can only be a conic section, which to my knowledge cannot have an âSâ form.

I am well and truly up against time right now but these very simple queries dont need illustrations, surely ?

this should be easily imaginable in the mk1 brain though I had thoughtâŚ

take a pencil and paper and draw a shallow arc with a sweep of the wrist, then stab at it quickly with your non writing hand and the pencil along the arc, those are our points.

now draw a degree 2 curve through them as best fit.

How is that done ?

All I can find are tools that create a deg3 curve best fit and I get an S curve as some of those points allow for such a fit.

Can a deg2 be drawn ?

aha I spy degree option in the control point curve and so enter 2, expecting my plotting through the points to generate a single bend curve, but get a deg 3 curve, many Sâs ! i.e its a wiggly curve !

so how does one draw a best fit curve which is a single arc type curve through points that have a bit of an S curve shape about them ?

Does question 4 why isnt there an arc best fit through points command need a drawing of an arc and some points it fits through. If there is a circle through points command, why isnt there an arc best fit points command ? No drawing needed for that surely ?

Well, they do, if you want an answer that fits your situation. Otherwise we can make something up that works perfectly, but isnât anything like what you are describing.

Curves that donât have a constant radius are NOT arcs. If your points are not arranged in an âarchingâ shape, then drawing a curve through them wonât arch either.

The Fair command is what comes to mind here- it is designed to smooth out rapid changes in curvature. Give it a larger tolerance, or use repeatedly at a smaller tolerance (probably better result)

Just for the intellectual exercise, I wrote a script that allows you to create a âbest-fitâ arc through an arbitrary set of point objects. You need to select the arc start and endpoints in the first pick, then all the rest in the second. It then calculates the entire set of 3 point arcs possible (one through each intermediate point that was selected), gets the average radius of all, and runs an arc of that radius between the start and end points.