How do I plot all the points on a matrix (in 3d) with the x and y being the locations of the elements of the matrix, and the z being the value of the elements?

Hello!

I have a question. I am trying to make a scatter plot in 3d, with a 49 by 49 matrix as a starting value. My end goal would be to have 2401 (49x49) points, with each point being at the x and y value of the row and collum of the respective matrix element, and have the z be the value of the element.

Basically, I want to graph every point in the 2d matrix in 3d without having to separate each point of the matrix out and graph it. If this is not clear, please tell me.

Thank you so much to everyone who replies!

-Kevin

[KSSV]

As the matrix is 3D...may be (x,y) for each matrix will be same....so, you can plot one matrix as one layer at once....or manually assign some z value as height and plot all at once....am I right?

[Kevin Shen]

The matrix is 2d, I just want to make a 3d scatter plot from the 2d matrix, with the x pos of the dot being the row, the y pos being the collum, and the z being the value inside the element of the matrix

Answer 1

[Star Strider]

Try this:

M = rand(49);                                       % Original Matrix
[rv,cv] = ndgrid(1:size(M,1), 1:size(M,2));         % Create Index Vectors For ‘M’

figure
scatter3(rv(:), cv(:), M(:))                        % 3D Scatter Plot Using ‘scatter3’

.

[Kevin Shen]

Thanks, but instead of random positions for each of each point how would I make each point's z position be the value of the element in the matrix?

[Star Strider]

Indexing in MATLAB is such that this plot should do just that. The (:) subscript convention forces the ‘rv’, ‘cv’ and ‘M’ matrices to be vectors using linear indexing. (Note that ‘rv’ are the row indices, and ‘cv’ are the column indices.)

Considering a smaller example:

M = randi(9,4)                                      % Original Matrix
[rv,cv] = ndgrid(1:size(M,1), 1:size(M,2));         % Create Index Vectors For ‘M’

Result = [rv(:), cv(:) M(:)]

producing (in this random example):

M =
     8     7     8     3
     7     6     6     1
     2     6     9     1
     2     2     6     7

and:

Result =
     1     1     8
     2     1     7
     3     1     2
     4     1     2
     1     2     7
     2     2     6
     3     2     6
     4     2     2
     1     3     8
     2     3     6
     3     3     9
     4     3     6
     1     4     3
     2     4     1
     3     4     1
     4     4     7

so the relevant values of ‘rv(:)’, ‘cv(:)’ and ‘M(:)’ conserve the appropriate array indices, and then will if plotted:

figure
stem3(rv(:), cv(:), M(:), 'filled')

I chose stem3 here because it is easier to see where the points belong with respect to the x- and y-axes. The scatter3 plot would be the same, although without the stems.

.

[Kevin Shen]

Ah, I see, thanks so much! I was just a bit confused on the random part, but that was just to create the matrix. Thanks for explaining everything so nicely!

[Star Strider]

As always, my pleasure!

I very much appreciate your compliment!