Fill below the 3D terrain data

A=imread('appRasterNEDAPIService1708354512850-756880040.tif');
X=1:324;
Y=1:194;
[X,Y]=meshgrid(X,Y);
surf(X,Y,A)

Hello. I have this terrain data. The size of A matrix is 194x324 and contain elevation data. I want to fill below the terrain from the elevation of the data to the 0 (mean sea level). I use fill code

hFill = fill3(X, Y, A, patchColor, 'LineWidth', 1, 'EdgeColor', patchColor, ...
              'FaceAlpha', 0.5);

However, it only fill below the surface with thin layer. I try to fill from the elevation to the 0 (mean sea level).

Thank you,

Answer 1

[Tejas]

Hello Burak,

To fill the terrain from the elevation data down to mean sea level, you can create polygons that act like vertical planes or walls. These polygons start at the terrain surface and extend down to the z-plane at 0, which represents sea level.

Here is a code snippet demonstrating how this can be achieved:

patchColor = [0.5, 0.5, 0.5]; % Gray color 
for i = 1:size(A, 2) 
    x = [X(:, i); flipud(X(:, i))]; % x cordinates for ith polygon 
    y = [Y(:, i); flipud(Y(:, i))]; % y cordinates for ith polygon 
    z = [zeros(size(A, 1), 1); flipud(A(:, i))]; 
    
    fill3(x, y, z, patchColor, 'EdgeColor', 'none', 'FaceAlpha', 0.5); 
end 

Below is a screenshot of the output using sample data, showing how the terrain will appear:

For a better understanding of this solution, refer to the documentations below:

• fill3: https://www.mathworks.com/help/releases/R2023b/matlab/ref/fill3.html
• flipud: https://www.mathworks.com/help/releases/R2023b/matlab/ref/flipud.html

[burak ergocmen]

Thank you for the answer,

Yes it is working but it is for the last slice. The size of the Matrix A is 194x324.

z = [zeros(size(A, 1), 1); flipud(A(:, i))]; 

I think it takes only the last slice of the terrain. The final of the z matrix is 388x1 ..

[Tejas]

By "last slice", are you referring to the last column of matrix A?

[burak ergocmen]

Yes, I think the problem is about the z .

First, I use my code and related A matrix and X Y is attached..

patchColor = [0.5, 0.5, 0.5]; % Gray color 
for i = 1:size(A, 2) 
    x = [X(:, i); flipud(X(:, i))]; % x cordinates for ith polygon 
    y = [Y(:, i); flipud(Y(:, i))]; % y cordinates for ith polygon 
    z = [zeros(size(A, 1), 1); flipud(A(:, i))]; 
    
    fill3(x, y, z, patchColor, 'EdgeColor', 'none', 'FaceAlpha', 0.5); 
end 

After the code above, the related figure is given below:

Thank you,

[Tejas]

Hi Burak,

The issue arises because the 'hold' function has not been used. This causes the polygon plot for a column of matrix A to overwrite the existing plot. For more details on the 'hold' function, refer to this documentation: https://www.mathworks.com/help/releases/R2023b/matlab/ref/hold.html

Try this code snippet:

load("terrain.mat");
% Plot the terrain surface
figure;
surf(X, Y, A);
hold on;
patchColor = [0.5, 0.5, 0.5]; % Gray color
for i = 1:size(A, 2)
    x = [X(:, i); flipud(X(:, i))]; % x cordinates for ith polygon
    y = [Y(:, i); flipud(Y(:, i))]; % y cordinates for ith polygon
    z = [zeros(size(A, 1), 1); flipud(A(:, i))];
    fill3(x, y, z, patchColor, 'EdgeColor', 'none', 'FaceAlpha', 0.5);
end
% Adjust plot settings
xlabel('X');
ylabel('Y');
zlabel('Elevation');
title('3D Terrain with Filled Base');
view(3);
axis tight;
hold off;

Here is a screenshot of the output:

[burak ergocmen]

thank you it is really helpful

Best wishes