# Marking specific points on a 3D curve

Here is the curve below. (written as a position vector)

r = {Cos[7 Pi*t], Cos[6.2*Pi*t], 2.5*t}
ParametricPlot3D[r, {t, 0, 2}]


I want to know how I can mark specific points on this curve, for example when t = 0 and t=1.

I would also like to label those points.

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You should start with checking related posts, see e.g. How to get intersection values from a parametric graph? Three dimensional problem is not especially more difficult, nevertheless it depends on what kind of visualization you expect, see e.g. Finding unit tangent, normal, and binormal vectors for a given r(t) for vectors instead of points. –  Artes Jun 16 at 14:56

You can also use MeshFunctions but you need to "cheat" to include the t=0 point, e.g.

This is an edited post based on the correct comments by Oska and gpap. In my original answer I used the equivalent of Function[{x,y,z,t},z] though my intention was Function[{x,y,z,t},t]. I have corrected and now labelled the points.

r[t_] := {Cos[7 Pi*t], Cos[6.2*Pi*t], 2.5*t};
Show[ParametricPlot3D[r[t], {t, -0.01, 2}, MeshFunctions -> (#4 &),
Mesh -> {{0., 1}}, MeshStyle -> {PointSize[0.03], Red}],
Graphics3D[
Text[Framed[#1], r[#2], {1, -1}] &, {{"Position 1",
"Position 2"}, {0, 1}}]]]


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is there a way i can label those points? –  Lebouski Jun 17 at 13:41
Shouldn't be the end point (t = 2) placed at the end of the curve? The t=1 point is wrong as well I'm afraid. –  Öskå Jun 17 at 14:14
@Oska the OP specifically mentions t=0 and t=1 hence my mesh points...I have only displayed and not labeled so will revise when I get chance –  ubpdqn Jun 17 at 20:07
What I meant is that.., since the function is plotted from 0 to 2, for t=2 the point should be in the end right? (at the top in that case) –  Öskå Jun 17 at 20:16
@Öskå is right. Your mesh function is now labelling the curve at the point where its z value is 1 and not at the point where the parameter t is 1. In ParametricPlot3D the option MeshFunctions takes four arguments, the x, y, z coordinates and the parameter along the curve. You can either replace MeshFunctions -> (#3/2.5 &) or MeshFunctions -> (#4 &) to get the right result. Then you'll have (at least) an upvote :) –  gpap Jun 18 at 9:22

You can use Graphics3D and Show:

r[t_] := {Cos[7 Pi*t], Cos[6.2*Pi*t], 2.5*t} ;
Show[ParametricPlot3D[r[t], {t, 0, 2}],
Graphics3D[{
PointSize@0.05, Point[r[#] & /@ {0, 1}],
Text[#, #2] & @@@
Thread[{{"Start", "Middle"}, {0, 0, .2} + # & /@ (r@# & /@ {0, 1})}]}]]


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Another way to use Mesh (credit: this answer by @BobHanlon )

r = {Cos[7 Pi*t], Cos[6.2*Pi*t], 2.5*t};

ParametricPlot3D[r, {t, 0, 2},  Mesh -> {{#, {PointSize[0],
Text[Framed@Style[Round@#, Red, Bold, 16], r /. t -> #]}} & /@ {0.00001, 1, 1.99999}}]


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