通过最佳拟合法【BESTFIT】建立坐标系,意味着使坐标系尽量贴近被测元素。旋转和平移坐标系直到找到一个合适的位置,此时,被测元素与其名义数据的偏差最小。
通常最佳拟合是在六个自由度上进行的,但操作者也可以限制一些旋转和/或平动自由度。
例如:平面上均布的八个孔做最佳拟合,我们通常会限定其绕Y,Z轴旋转的操作,以及沿乙轴平移的操作。
最佳拟合【BESTFIT】有两种不同的算法:根据所使用的元素全部是点类元素,还是其它带方向的元素,有所区别。
在最佳拟合【BESTFIT】中,当选中的几何元素不仅仅是点,坐标系计算方法如下:
使被测元素的特性点与名义点之间的距离为最小。
使被测元素的方向余弦与名义方向余弦最大限度地平行。
在最佳拟合【BESTFIT】中,当选中的几何元素仅仅是点时,坐标系的计算目的是使被测量的元素特性点与名义点之间的距离为最小。
两种不同的计算法的使用是根据仅仅是点坐标还是一般平面穿过点的坐标。
$$/* Header
DMISMN/'Created by [爱科腾瑞科技(北京)有限公司-091521-DEMO-11022(华清)] on 星期五, 六月 18, 2021', 4.0
UNITS/MM, ANGDEC, MMPS
WKPLAN/XYPLAN
PRCOMP/ON
TECOMP/ON
FLY/1.0000
MODE/MAN
SNSET/APPRCH, 2.0000
SNSET/RETRCT, 2.0000
SNSET/DEPTH, 0.0000
SNSET/SEARCH, 10.0000
SNSET/CLRSRF, 20.0000
RECALL/D(MCS)
SNSLCT/S(40-D2)
GEOALG/BF, LSTSQR
GEOALG/ANGLB, DEFALT
GEOALG/CIRCLE, LSTSQR
GEOALG/ARC, LSTSQR
GEOALG/PLANE, LSTSQR
$$
$$
$$*/
MODE/MAN
F(CIR1)=FEAT/CIRCLE,INNER,CART,0.0000,-0.0000,-0.0000,0.0000,0.0000,1.0000, 20.0000
F(CIR2)=FEAT/CIRCLE,INNER,CART,60.0000,-0.0000,-0.0000,0.0000,0.0000,1.0000, 20.0000
F(CIR3)=FEAT/CIRCLE,INNER,CART,30.0000,20.0000,-0.0000,0.0000,0.0000,1.0000, 12.0000
$$ Empty VECBLD Block
RMEAS/CIRCLE, F(CIR1), 5, VECBLD, 2.0000, 3
ENDMES
$$ Empty VECBLD Block
RMEAS/CIRCLE, F(CIR2), 5, VECBLD, 2.0000, 3
ENDMES
$$ Empty VECBLD Block
RMEAS/CIRCLE, F(CIR3), 5, VECBLD, 2.0000, 3
ENDMES
$$ [CIR1]CIRCLE 元素不需要重新测量
$$ [CIR2]CIRCLE 元素不需要重新测量
$$ [CIR3]CIRCLE 元素不需要重新测量
DMESW/COMAND,'D(CRD1) = LOCATE/XYZDIR, XYZAXI, $
FA(CIR1), XYZAXI, $
FA(CIR2), XYZAXI, $
FA(CIR3), XYZAXI'
(ITR_START)
F(CIR1)=FEAT/CIRCLE,INNER,CART,-0.0000,0.0000,0.0000,0.0000,0.0000,1.0000, 20.0000
F(CIR2)=FEAT/CIRCLE,INNER,CART,60.0000,0.0000,0.0000,0.0000,0.0000,1.0000, 20.0000
F(CIR3)=FEAT/CIRCLE,INNER,CART,30.0000,20.0000,0.0000,0.0000,0.0000,1.0000, 12.0000
DMESW/COMAND,'D(CRD2) = LOCATE/XYZDIR, XYZAXI, $
FA(CIR1), XYZAXI, $
FA(CIR2), YZAXIS, $
FA(CIR3), ZAXIS'
KNPTR1 = ITERAT/(ITR_START), (ITR_FAIL), 0.030000, ABSL, 10,$
FA(CIR1), 1, 1, 1,$
FA(CIR2), 0, 1, 1,$
FA(CIR3), 0, 0, 1
(ITR_FAIL)