This is a nerdy detail about the technical Background of UDT - and wether the help is correct: The help for FlowalongSrf says that “objects are refit”. I always thought that curves and surfaces are refined by adding Knots. This is also what is stated at _matchSrf help "Rhino adds knot lines to t…

@Tom_P the information about UDT is correct

[image] Gijs de Zwart: correct its a refit, not adding knots ? are you sure ? refiting what ? my guess would be, some sample points are used and where ever the new geometry is of, a knot is added. this can be repeated until all sample points are within tolerance. But with refitting ? how s…

In the process of refitting, knots will be added. Maybe your question is more about terminology?

[image] Gijs de Zwart: terminology maybe. i am irritated by the link to refit . help - flowAlongSrf: objects are refit as needed help - matchSrf: adds knot lines to the modified surface or surfaces until the surfaces are within tolerance (for me this is very clear) does refit mean - adding…

[image] Tom_P: I thought refit can also reduce the complexity of a surface / curve Well, there ist that . I have noticed, while putting together transitioning to Rhino guidelines, that the terminology is somewhat inconsistent or obscure, as in the above example “knot lines”, which in other su…

In Bulgarian language, typically we don’t say the translation of “curve”, which is “крива”. Instead, we say “права линия” to the straight lines, and “крива линия” or “извита линия” (“crooked line”, “distorted line”, “bent line”, “curved line”) to the curves. The reason for that is because “крива” ha…

[image] Lagom: as in the above example “knot lines”, which in other surface modellers are “isoparametric curves” (“real” isocurves from knots, not “display” isocurves, which, I must say, I find misleading) “Iso” as a prefix means “same” or “equal”. Any curve on a surface which is generated by…

In industrial design and transportation design NURBS surface modelling (no idea about architecture, shoes, and ship hulls), one is interested in one thing only - isoparametric curves from a curve’s or adjacent surface boundary’s knots, to see the spans of a surface one is building, so one can reduce…

Do you mean degree 1 lines only? I’m asking, because a 1 kilometer long perfectly straight line with 3 control points is still a line. It just has an extra point somewhere along its straight vector. However, the moment one moves any of the control points by 1 micron, that line will no longer be a tr…

To display the locations and number of knot curves of a surface and no other isocurves set isocurve density to 0. Then an isocurve will only displayed at the surface knots, ie only knot curves. The default setting for isocurve display can be set in Options > General. Isocurve density can also be set…

UDT FlowAlongSrf - refit vs. refine/addKnot

Rhino

brian (Brian Gillespie) January 21, 2026, 7:06pm 18

RH-91541 is fixed in Rhino WIP

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When do I need to Rebuild, refit or use another technique? Thanks! Rhino for Windows windows	8	131	February 7, 2026
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UDT FlowAlongSrf - refit vs. refine/addKnot

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