This graphics object can be used to do vector drawing on the Sprite. For example, see the code to draw a circle of radius 5.

这个图片对象可被用来在sprite上进行矢量作图。

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So, for a sphere, the normal vector is divided by the radius of the sphere.

关于球体，法向量是,除以球的半径。

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We have a sphere of radius a. I have my vector field.

先作出半径为a的球面，再画出给定的向量场。

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