MATLAB Help Needed: Find Volume Under Surf/Contour Plot

[Lebak]

I need help finding the volume underneath this surf plot. Or contour plot. We have a project including a sandbox with different heights of sand at different points. So create the plot I have used

x = [50:50:950];
y = [50:50:950];
z = 'values from an xls spreadsheet. Containing every height value with 50mm spacing from 50 mm to 950 mm in both x and y directions'.

[c,h] = contourm(x,y,z)
ht=clabel(c,h);
That's all I've done so far, I need to find the volume of sand in our sand box, and I know the width and length of it and also the height at those different locations.

Please help, I'm completely lost!

 

[marcusl]

You should "integrate" the values just as you would in calculus. Since you have discrete values in your spreadsheet, sum them together and multiply by the grid cell area, according to the rectangle method of calculus. (You can be fancy and use the trapezoidal rule or Simpson's rule, but you probably don't need the extra accuracy.) You can do this in Excel.