plot3 for 3D lines in MATLAB - Mini Project: Build & Apply

Plotting 3D Lines Using plot3 in MATLAB

📖 Scenario: You are working on a simple 3D visualization for a small engineering project. You want to draw a line in 3D space to represent a wire connecting two points.

🎯 Goal: Build a MATLAB script that uses plot3 to draw a 3D line between two points with given coordinates.

📋 What You'll Learn

Create vectors for the x, y, and z coordinates of the two points

Create a variable for line color

Use plot3 to draw the 3D line connecting the points

Display the plot with axis labels

💡 Why This Matters

🌍 Real World

3D line plots are useful in engineering and science to visualize paths, trajectories, or connections in space.

💼 Career

Knowing how to plot 3D data helps in fields like mechanical engineering, robotics, and data visualization.

1

DATA SETUP: Define the coordinates of two points

Create three vectors called x, y, and z each containing exactly two values: x = [1 4], y = [2 5], and z = [3 6].

MATLAB

% Create vectors x, y, and z with the given values
% Your code here

Hint

Use square brackets to create vectors in MATLAB, for example: x = [1 4];

2

CONFIGURATION: Define the line color

Create a variable called lineColor and set it to the string 'r' to represent a red line.

MATLAB

x = [1 4];
y = [2 5];
z = [3 6];
% Define the line color as red
% Your code here

Hint

Use single quotes to define a character vector for color in MATLAB, like 'r' for red.

3

CORE LOGIC: Plot the 3D line using plot3

Use plot3 with the vectors x, y, and z and the color variable lineColor to draw the 3D line.

MATLAB

x = [1 4];
y = [2 5];
z = [3 6];
lineColor = 'r';
% Plot the 3D line
% Your code here

Hint

Use plot3(x, y, z, lineColor) to plot a 3D line with the specified color.

4

OUTPUT: Add axis labels and display the plot

Add labels to the x, y, and z axes using xlabel, ylabel, and zlabel with the texts 'X-axis', 'Y-axis', and 'Z-axis' respectively. Then run the script to display the plot.

MATLAB

x = [1 4];
y = [2 5];
z = [3 6];
lineColor = 'r';
plot3(x, y, z, lineColor);
% Add axis labels below
% Your code here

Hint

Use xlabel('X-axis'), ylabel('Y-axis'), and zlabel('Z-axis') to label the axes.

Practice

1. What does the MATLAB function plot3(X, Y, Z) do?

easy

A. Plots a 3D line or points using vectors X, Y, and Z as coordinates.

B. Creates a 2D plot using X and Y only.

C. Generates a histogram of the data in X, Y, and Z.

D. Plots a pie chart based on the values in X, Y, and Z.

Solution

1. Step 1: Understand the function purpose

   plot3 is designed to plot lines or points in three-dimensional space using three vectors: X, Y, and Z.

2. Step 2: Compare options with function behavior

   Only Plots a 3D line or points using vectors X, Y, and Z as coordinates. correctly describes plotting in 3D using X, Y, and Z coordinates. Other options describe 2D plots or unrelated chart types.

3. Final Answer:

   Plots a 3D line or points using vectors X, Y, and Z as coordinates. -> Option A

4. Quick Check:

   plot3 = 3D line plot [OK]

Hint: Remember plot3 needs three coordinate vectors X, Y, Z [OK]

Common Mistakes:

• Thinking plot3 creates 2D plots
• Confusing plot3 with histogram or pie chart functions
• Using only two vectors instead of three

2. Which of the following is the correct syntax to plot a red dashed 3D line using plot3?

easy

A. plot3(X, Y, Z, 'rd')

B. plot3(X, Y, Z, 'r--')

C. plot3(X, Y, Z, color='red', linestyle='dashed')

D. plot3(X, Y, Z, 'red-dash')

Solution

1. Step 1: Recall MATLAB LineSpec format

   MATLAB uses short codes like 'r' for red and '--' for dashed lines combined as 'r--' in plot3.

2. Step 2: Evaluate each option

   plot3(X, Y, Z, 'r--') uses correct LineSpec syntax. plot3(X, Y, Z, 'red-dash') uses invalid string. plot3(X, Y, Z, color='red', linestyle='dashed') uses Python-like syntax, invalid in MATLAB. plot3(X, Y, Z, 'rd') 'rd' means red diamond marker, not dashed line.

3. Final Answer:

   plot3(X, Y, Z, 'r--') -> Option B

4. Quick Check:

   LineSpec 'r--' = red dashed line [OK]

Hint: Use 'r--' for red dashed line in plot3 [OK]

Common Mistakes:

• Using full words like 'red' or 'dashed' instead of codes
• Confusing marker codes with line style codes
• Trying Python-style named arguments

3. What will be the output of the following MATLAB code?

X = 1:3; Y = [2 4 6]; Z = [3 6 9]; plot3(X, Y, Z, 'g-o'); grid on; xlabel('X-axis'); ylabel('Y-axis'); zlabel('Z-axis');

medium

A. An error because vectors X, Y, Z have different lengths.

B. A 2D green line plot with circle markers on X and Y only.

C. A 3D scatter plot without lines connecting points.

D. A green 3D line with circle markers connecting points (1,2,3), (2,4,6), (3,6,9) with grid and axis labels.

Solution

1. Step 1: Analyze vectors and plot3 call

   X, Y, Z are vectors of equal length 3. plot3 with 'g-o' plots green lines with circle markers connecting points in 3D.

2. Step 2: Understand grid and labels

   grid on adds grid lines. xlabel, ylabel, and zlabel add axis labels. So the plot is a labeled 3D line with markers and grid.

3. Final Answer:

   A green 3D line with circle markers connecting points (1,2,3), (2,4,6), (3,6,9) with grid and axis labels. -> Option D

4. Quick Check:

   plot3 with equal vectors and 'g-o' = green line with circles [OK]

Hint: Equal length vectors plot connected 3D lines with markers [OK]

Common Mistakes:

• Assuming 2D plot instead of 3D
• Thinking different vector lengths cause error here
• Confusing scatter plot with plot3 line plot

4. Identify the error in this MATLAB code snippet:

X = 1:4; Y = [2 3 4]; Z = [5 6 7 8]; plot3(X, Y, Z);

medium

A. Vectors X, Y, and Z must have the same length to plot3.

B. plot3 requires the vectors to be row vectors only.

C. The plot3 function cannot plot more than 3 points.

D. Missing line style argument causes syntax error.

Solution

1. Step 1: Check vector lengths

   X has length 4, Y has length 3, Z has length 4. plot3 requires all three vectors to have the same length.

2. Step 2: Understand consequences of length mismatch

   Because Y is shorter, MATLAB will throw an error about vector size mismatch when calling plot3.

3. Final Answer:

   Vectors X, Y, and Z must have the same length to plot3. -> Option A

4. Quick Check:

   Equal vector lengths required for plot3 [OK]

Hint: Check all coordinate vectors have same length before plot3 [OK]

Common Mistakes:

• Assuming plot3 accepts different length vectors
• Thinking row vs column vector matters here
• Believing line style argument is mandatory

5. You want to plot two 3D lines on the same figure: one blue solid line and one red dashed line. Which code correctly does this?

hard

A. plot3(X1, Y1, Z1, 'b-'); hold off; plot3(X2, Y2, Z2, 'r--');

B. plot3(X1, Y1, Z1, 'b-'); plot3(X2, Y2, Z2, 'r--');

C. plot3(X1, Y1, Z1, 'b-'); hold on; plot3(X2, Y2, Z2, 'r--'); hold off;

D. plot3(X1, Y1, Z1, 'b-'); hold on; plot3(X2, Y2, Z2, 'r--'); hold on;

Solution

1. Step 1: Understand hold on/off usage

   To plot multiple lines on the same figure, hold on keeps the current plot so new plots add to it. hold off releases it.

2. Step 2: Analyze each option's hold usage

   plot3(X1, Y1, Z1, 'b-'); hold on; plot3(X2, Y2, Z2, 'r--'); hold off; correctly uses hold on before second plot and hold off after to finish. plot3(X1, Y1, Z1, 'b-'); plot3(X2, Y2, Z2, 'r--'); misses hold so second plot overwrites first. plot3(X1, Y1, Z1, 'b-'); hold off; plot3(X2, Y2, Z2, 'r--'); calls hold off too early. plot3(X1, Y1, Z1, 'b-'); hold on; plot3(X2, Y2, Z2, 'r--'); hold on; calls hold on twice unnecessarily.

3. Final Answer:

   plot3(X1, Y1, Z1, 'b-'); hold on; plot3(X2, Y2, Z2, 'r--'); hold off; -> Option C

4. Quick Check:

   Use hold on/off to plot multiple lines [OK]

Hint: Use hold on before second plot, hold off after [OK]

Common Mistakes:

• Not using hold on causes plots to overwrite
• Calling hold off too early removes previous plots
• Calling hold on multiple times unnecessarily