Correct. But curves with internal knots can also be uniform. It depends on the parameter intervals between the knots.
yes I knew that.
maybe he said that to make things easier for me
I would like to know the role and the interest of the curves not uniform in rhino
how does that help in modeling?
and what is their use?
One use of non-uniform curves is interpoloting curves. Frequently better results are obtained from InterpCrv or CurveThroughPts if the Knots=Chord option is used instead of Knots=Uniform. Knots=Chord creates the knot vector (list of knot parameter values) based on the distance between the interpolation points which are usually unequal. The result is a non-uniform curve. Here is an example of what the difference can be when using CurveThroughPts.: Uniformvsnonuniform1.3dm (38.0 KB)
Non-uniform curves are created if knots are added to allow refinement of a curve or if knots are removed to simplify a curve.
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thank you davide for the answer
this is a way to manipulate the location of the Knots.
this allows to define the exact location of the Knots.
if we then want to divide the curves multi-span , to have a curves of a single span easily
in the past I tried to move the knots
yet I don’t know if this is possible in another CAD application 
.but I never thought if the curve is uniform or not
this made me understand that if the knots is defined or randomly placed by the user. the curve becomes non-uniform automatically
if I increase the degree of a multi-span curves, it becomes non-uniform because of the multiple knots
. I said upstairs
I built my understanding of knots uniform and non-uniform, from the fact that I did a little test on rhino, which made me think that the distance between the knots, is the only factor which defines the curves if it is uniform or not.
you will see it in this video,
when I place the knots evenly on the curve, it is always uniform.
however when I place them haphazardly, the curve transforms into non-uniform.
now I know that the knots can have different distances and be uniform at the same time
Hello - to insert knots and keep better (though not, I think, always strict) uniformity use the MidPoints=Yes option on InsertKnot and snap to the marked points. ‘Automatic’ will split each existing span with a new knot.
-Pascal
Inserting knots will only result in uniform spacing if a new knot is inserted at the mid-point of each original span which the Automatic option of InsertKnot does. If the curve has 5 spans then 5 knots need to be inserted for the curve to remain uniform.
thank you pascal for the reminder
I completely forgot these options