# How can I get a curve from a trace, and calculate it's length?

Nicholasfox shared this question 2 years ago

As follow:

I want to know the length of the trace of point P. Can I get a curve from a trace, or there's a direct way to calculate it's length?

Thanks.

What you see in the algebra view is not exact the definition of the object.

You can see the definition for example in the Properties/Basic/Definition.

In the attachment it has some explanations. If not clear then please ask more specifically.

1

Bonjour ,

ça ressemble à une fonction sinus mais il faudrait savoir comment est défini le point P

Cordialement

2

If we think a little bit more direct to reduce dependencies to one variable t (k),

we get a term of the moving point P and do integrate to the arc length

this is called Zykloide - Rollkurve

there exist a command Locus( <Point Creating Locus Line>, <Slider> )and LocusEquation( <Locus> )

but I was not very successful with it...

1

It is instructive，Thanks!

2

With the parameter equation for cycloids (wikipedia) and with Locus()

1

Amazing, I need some time to figure it out.Thank you, very much.

2

Advanced: more general parameter equation for a and a' and more independent.

1

Hi, how comes this Expression? I really can't understand.

2

What you see in the algebra view is not exact the definition of the object.

You can see the definition for example in the Properties/Basic/Definition.

In the attachment it has some explanations. If not clear then please ask more specifically.

1

I knew the basic usage of ggb, I just don't know the concept of the Cycloid/Trochoid/.

Your help was very much appreciated！