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Creating a vector from two points using 3 coordinates

Asked by Anton van den Bedem on 12 Jun 2019
Latest activity Commented on by Guillaume
on 12 Jun 2019
I'm trying to create two vectors from two points created from a set of data. The data set contains 3106 values. I need something like a loop for this to work, so i can plot the length of these two vectors over time.
fyi: The vectors are the force projected on the ground while running.
In the end I need an array of the length of both vectors.
This is what i got so far:
j = 1:10:length(Data.Time)
x0_l=Data.XPC_FP1COP(j,1);
y0_l=zeros(length(Data.Time),1);
z0_l=Data.XPC_FP1COP(j,2);
x0_r=Data.XPC_FP2COP(j,1);
y0_r=zeros(length(Data.Time),1);
z0_r=Data.XPC_FP2COP(j,2);
x_l=Data.XPC_FP1GRF(j,1);
y_l=Data.XPC_FP1GRF(j,1);
z_l=Data.XPC_FP1GRF(j,1);
x_r=Data.XPC_FP2GRF(j,1);
y_r=Data.XPC_FP2GRF(j,1);
z_r=Data.XPC_FP2GRF(j,1);
Ground_l = [x0_l,y0_l,z0_l];
Ground_r = [x0_r,y0_r,z0_r];
Top_l = [x_l,y_l,z_l];
Top_r = [x_l,y_l,z_l];
F_l = Ground_l - Top_l
F_r = Ground_r - Top_r

  3 Comments

You haven't actually asked a question, so it's unclear what help you need. You've given us some code (which I don't think will work because the length of the y0_? vectors won't match the length of the x0_? and z0_? vectors) but don't really tell us what it's meant to do.
Okay, I'll try to rephrase.
I have got data of a starting point and an ending point of a vector. Of both these points I have a matrix of 3160x3, being measurements for x, y and z. each row being a certain time that the point was measured. What I want the code to do is to eventually plot the length of this line between the two points against time. How do I get this to work?
Is this clearer?
I rewrote the code that I have below. I also changed the y0, so that it corrosponds with the lengths of x0 and z0.
j = 1:10:length(Data.Time)
x0 = Data.XPC_FP1COP(j,1);
y0 = zeros(length(j),1);
z0 = Data.XPC_FP1COP(j,2);
x = Data.XPC_FP1GRF(j,1);
y = Data.XPC_FP1GRF(j,2);
z = Data.XPC_FP1GRF(j,3);
Start = [x0,y0,z0];
End = [x,y,z];
F = End - Start
My understanding is that you have two points moving through a 3D space. And it sounds like the distance between these two points vary in time.
No idea what the length of the line refers to? What line? Do you mean that you want to plot the distance between the two points with time?
And by distance, do you mean euclidean distance (i.e )?

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1 Answer

Answer by Matt J
on 12 Jun 2019
Edited by Matt J
on 12 Jun 2019
 Accepted Answer

I think this would complete your code.
Times=1:10:length(Data.Time);
J=numel(Times);
F=nan(J,3);
for j = 1:J
x0 = Data.XPC_FP1COP(j,1);
y0 = zeros(length(j),1);
z0 = Data.XPC_FP1COP(j,2);
x = Data.XPC_FP1GRF(j,1);
y = Data.XPC_FP1GRF(j,2);
z = Data.XPC_FP1GRF(j,3);
Start = [x0,y0,z0];
End = [x,y,z];
F(j,:) = End - Start;
end
plot(vecnorm(F,2,2))

  1 Comment

Is there any point to the loops? I would assume that:
rows = 1:10:numel(Data.Time); %and if Data is a table use height(Data)
F = Data.XPC_FP1GRF(rows, 1:3) - [Data.XPC_FP1COP(rows, 1), zeros(numel(rows), 1), Data.XPC_FP1COP(rows, 3)];
plot(vecnorm(F, 2, 2));
would achieve the same result.

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