a series of point coordinates are known, and their orientation (angle). Calculate gradient

For example, 10 points' coordinates are known, as (xi, yi) i =1 ... 10 and a corresponding angle of each point is known, as ai

How I can calculate the gradient of each point and How does it show an arrow on the image for each point?

Thanks.

Answer 1

[Image Analyst]

How can a bunch of points in a 2D plane, scattered all over the place, have a gradient? How did you get the angle at those points, but not the magnitude ?

Anyway, you can use quiver to put arrows on the picture.

[ZhG]

 I did it like
u = c*cos(ai)
v = c*sin(ai)

c is a constant, 0.2 for example

quiver(x,y u, v)

[ZhG]

but the line with arrow is a little longer than I expected How can I control that?