RationalDMIS 2020 用3D直线建立坐标系
建立坐标系的目的（原因）：
（1）产品固定到三坐标上，不能保证产品基准的方向与三坐标坐标轴的方向完全一致；
（2）涉及到坐标轴方向的距离无法求取；
（3）二维的几何公差GD&T（即形位公差）无法求取，比如位置度；
（4）点的矢量方向不正确，导致半径补偿不对；
（5）产品上所有的孔（和柱）都是空间圆，测量每个圆都需要关系平面指定；
（6）产品位置无法确定，不能使用程序自动测量，否则需要产品每次固定位置完全一致。
综上所述，测量前需要在产品上建立坐标系，也就是根据产品基准建立一个工件坐标系，这个坐标系习惯称为工件坐标系。
在实际测量中，零件的安放最好使用一定的夹具进行定位，这样测量每批同型号零件时只需对第一件进行手动测量建立坐标系即可，后续零件只要在夹具上进行简单的定位安装后即可自动进行测量，大大提高测量效率。
坐标系的第一轴为了能够与第二轴垂直，一般采用平面，因为平面的法向矢量与平面肯定是垂直的。如果第一轴采用圆柱轴线定义，则同时确定了与其相垂直的坐标平面。
建立（找正）第一轴必须用平面或轴线（N个圆柱（台阶圆柱）连线建第1轴的）。
1.采集基准元素，台阶圆柱最佳拟合3D直线
2.生成坐标构建坐标系
$$/* Header
DMISMN/'Created by [山涧果子] on 星期二, 三月 23, 2021', 4.0
UNITS/MM, ANGDEC, MMPS
WKPLAN/XYPLAN
PRCOMP/ON
TECOMP/ON
FLY/1.0000
MODE/MAN
SNSET/APPRCH, 2.0000
SNSET/RETRCT, 2.0000
SNSET/DEPTH, 0.0000
SNSET/SEARCH, 10.0000
SNSET/CLRSRF, 20.0000
RECALL/D(MCS)
SNSLCT/S(40-D2_A90_B180)
GEOALG/BF, LSTSQR
GEOALG/ANGLB, DEFALT
GEOALG/CIRCLE, LSTSQR
GEOALG/ARC, LSTSQR
GEOALG/PLANE, LSTSQR
$$
$$
$$*/
MODE/MAN
F(PLN1)=FEAT/PLANE,CART,8.0038,0.0000,-3.3014,0.0000,-1.0000,0.0000
$$ Measurement points are created through actual points
MEAS/PLANE, F(PLN1), 4
PTMEAS/CART, -20.7865, 0.0000, 16.9537, 0.0000, -1.0000, 0.0000
PTMEAS/CART, -31.4453, 0.0000, -25.3292, 0.0000, -1.0000, 0.0000
PTMEAS/CART, 41.9377, 0.0000, -27.3484, 0.0000, -1.0000, 0.0000
PTMEAS/CART, 42.3091, 0.0000, 22.5182, 0.0000, -1.0000, 0.0000
ENDMES
F(CYL1)=FEAT/CYLNDR,INNER,CART,0.0000,11.9027,-0.0000,-0.0000,-1.0000,0.0000, 30.0000, 18.0377
$$ Measurement points are created through actual points
MEAS/CYLNDR, F(CYL1), 8
PTMEAS/CART, 3.0525, 20.9216, -14.6861, -0.2035, 0.0000, 0.9791
PTMEAS/CART, 13.8661, 11.5021, 5.7211, -0.9244, 0.0000, -0.3814
PTMEAS/CART, -4.9000, 17.3420, 14.1771, 0.3267, -0.0000, -0.9451
PTMEAS/CART, -10.7941, 20.8116, -10.4158, 0.7196, -0.0000, 0.6944
PTMEAS/CART, -10.6516, 2.8839, -10.5615, 0.7101, -0.0000, 0.7041
PTMEAS/CART, 14.1486, 3.0955, -4.9817, -0.9432, 0.0000, 0.3321
PTMEAS/CART, 13.0051, 3.2139, 7.4744, -0.8670, 0.0000, -0.4983
PTMEAS/CART, -3.4861, 5.5108, 14.5893, 0.2324, -0.0000, -0.9726
ENDMES
SNSLCT/S(40-D2_A90_B0)
F(CYL2)=FEAT/CYLNDR,INNER,CART,0.0000,59.1754,-0.0000,-0.0000,1.0000,0.0000, 15.0000, 26.8074
$$ Measurement points are created through actual points
MEAS/CYLNDR, F(CYL2), 8
PTMEAS/CART, -4.9928, 47.0361, -5.5966, 0.6657, -0.0000, 0.7462
PTMEAS/CART, -7.0305, 45.7717, -2.6118, 0.9374, -0.0000, 0.3482
PTMEAS/CART, -2.8394, 55.8031, 6.9417, 0.3786, 0.0000, -0.9256
PTMEAS/CART, 5.5015, 64.1121, 5.0974, -0.7335, -0.0000, -0.6797
PTMEAS/CART, 1.2932, 71.5017, 7.3877, -0.1724, -0.0000, -0.9850
PTMEAS/CART, -5.7204, 72.3470, 4.8505, 0.7627, -0.0000, -0.6467
PTMEAS/CART, -3.2223, 72.5791, -6.7725, 0.4296, -0.0000, 0.9030
PTMEAS/CART, 7.3766, 72.5268, -1.3547, -0.9836, -0.0000, 0.1806
ENDMES
SNSLCT/S(40-D2)
F(CON1)=FEAT/CONE,INNER,CART,10.0000,32.0000,-32.9807,0.0000,-0.0000,1.0000, 30.0000
$$ Measurement points are created through actual points
MEAS/CONE, F(CON1), 8
PTMEAS/CART, 18.7369, 27.7604, 3.2621, -0.8690, 0.4217, 0.2588
PTMEAS/CART, 10.9457, 42.0734, 4.7790, -0.0903, -0.9617, 0.2588
PTMEAS/CART, -3.0921, 30.0449, 16.4215, 0.9553, 0.1427, 0.2588
PTMEAS/CART, 4.2662, 19.9320, 16.8828, 0.4145, 0.8725, 0.2588
PTMEAS/CART, 0.5070, 21.1582, 20.8000, 0.6363, 0.7267, 0.2588
PTMEAS/CART, -3.2056, 37.1530, 19.9226, 0.8998, -0.3511, 0.2588
PTMEAS/CART, 6.0085, 45.2712, 18.7398, 0.2782, -0.9250, 0.2588
PTMEAS/CART, 22.2344, 25.2993, 19.0785, -0.8472, 0.4640, 0.2588
ENDMES
F(LN_BF3D1)=FEAT/LINE,BND,CART,0.0000,11.9027,-0.0000,0.0000,59.1754,-0.0000
CONST/LINE,F(LN_BF3D1),BF,FA(CYL1),FA(CYL2)
F(PT_INTER1)=FEAT/POINT,CART,0.0000,0.0000,-0.0000,0.0000,-1.0000,0.0000
CONST/POINT,F(PT_INTER1),INTOF,FA(PLN1),FA(LN_BF3D1)
D(CRD1) = DATSET/FA(LN_BF3D1), YDIR, FA(CON1), ZDIR, FA(LN_BF3D1), ZORIG
D(CRD1) = TRANS/YORIG, FA(PT_INTER1), XORIG, FA(LN_BF3D1), ZORIG, -0
附注：说明
1）图纸上标注ABC基准A基准空间整列，B基准平面旋转，C基准原点指定。
（2）需要根据ABC基准的重要性来决定建立坐标系的步骤比如：B基准最重要，A基准次之，C基准再次之。这时操作如下：B基准空间整列，A基准平面旋转，C基准原点指定。
3）图纸上没有标注ABC基准，而是其他基准字母，比如基准ZEF这时最重要的基准空间整列，次之重要的基准平面旋转，再次之重要的基准原点指定。
（4）情况四--图纸上没有标注任何基准根据要素的重要性建立坐标系：比如比较大的平面和精加工的孔，也可根据垂直度和平行度来判断。
