说明：  庞加莱对连续运动的轨迹用一个截面(叫庞加莱截面)将其横截，那么根据轨迹在截面上穿过的情况，就可以简洁地判断运动的形态，由此所得图像叫庞加莱映像。
(Poincare maps Poincare's trajectory of continuous motion to a cross section (called Poincare cross section). Then we can judge the shape of motion succinctly based on the cross section of the track, and the resulting image is called Poincare image.)