Derivative of 2D array

[giansorr83]

Hello to everybody. I am elaborating some images of a turbulent jet. I am able to detect the contours of the jet with the related points. I want to compute the velocity field and the related stretch rate. So I need to compute the first and the second derivative of every point of my contour. The problem is that the points are not ordered. The Dx is very random and the contour presents a lot of vortex... I have tried to implemented a 5 costant central scheme to compute the derivative but it fails...I think that it depends from the structure of my data. Anybody could help me?

[torekp]

Give us more detail? How about a small subset of your data, e.g. 100x100 points in a tab-delimited spreadsheet. Provide X and Y axes, since you imply dX is not constant. And attach your VI.

[MarkCG]

So jet velocity call it "u(x,y)", is in Z direction, is function of x and y, and you want to take the derivative u_xx , u_yy ,and u_xy ? You might try to smooth the data with "2D interpolation scattered.vi" (look for example), found in math palette then take the derivative of the interpolating data/function.

There are higher order stencils you can use to compute the derivatives and Laplacian as well--- they can be derivatived by Taylor series expansion. This will help in smoothing the derivative function also.

[giansorr83]

I am sorry for this question but I am a new member of the community. How I can attach a vi?