Catia-V5-点云对齐初探.ppt

Digitized Shape Editor Aligning using the Compass 罗盘法对齐 罗盘法对齐：通过拽动罗盘进行对齐，是一种粗糙的对齐方式，一般用在最佳拟合对齐之前。 References can be either a set of clouds of points and/or surfaces, or a set of points (no mix allowed), Selecting References starts the computation of a transformation based on the inertia axes. l参考对象可以是多笔点云，多个面，多个点集，但不能是混合类型。 l当参考对象不为空时， 变亮，通过点击它可以对参考对象进行4 个位置的变换，若进行了该变换，接下来再点击罗盘移动的话，进行移 动的是参考对象（这一点有点奇怪！）。 l当参考对象为空时，本对齐根据移动对象的惯性坐标系进行手动变换 。 l第三个带叉的罗盘可以恢复到上一次点击“apply”的位置。 点显示的百 分比数 默认罗盘的原点是对象的质心，但可以通过按住“shift”拽 动罗盘，从而改变罗盘的原点。 Digitized Shape Editor Align with best fit 最佳拟合法对齐 在使用最佳拟合法进行对齐前，最好先使用罗盘对齐法将两个对象作简单大致的预对齐。 点云或网格 点云或网格或曲面，数量可多选，但类型必须一 致，若第一个选中曲面第二个选中点云，则默认 曲面作为实际参考对象参与运算。 由于对齐时是使用双方的所有的点，任何较大的 局部差异都会影响对齐结果，故需要想办法切除 不相同的区域再进行对齐。 偏差显示 Digitized Shape Editor Align with constraints 约束法对齐 This task shows you how to align a cloud of points with a reference by defining constraints (made of pairs of constraint elements) based on canonic shapes (points, lines, planes, spheres, cylinders, circles and their inverted elements) and applying a priority order on those constraints. 约束法对齐模式，通过定义多组约束关系来进行点云的对齐，这些约束关系可以由点，直线，圆，平面，球 ，圆柱等初等几何体之间的对应关系进行创建，同时这些约束关系在对齐时还具有优先级。此对齐法多适用 于较为规则的机械零件。 可以对一个对象创建多个约束，如一个平面可以建立与3个点的约束关系。 Be careful to have consistent constraints, regarding the geometry. For example: do not match three points with two different planes, if you match two normals to planes, be careful that they have the same orientation, when you select a cylinder or a circle, the constraint element taken into account is their center axis, i.e. a line. when you select a sphere, the constraint element taken into account is its center point. even if overconstraints are accepted, in some cases it might be necessary that the constraints form an isostatic system: A 3D object has 6 degrees of freedom, i.e. 3 translations and 3 rotations. Creating an isostatic system means that the 3 translations and the 3 rotations are locked. 创建约束时，所选取的几何元素，要保证该约束的一致性，如： 1，不要将3个点与2个平面进行约束； 2，2个法向与平面约束时，要保证方向的一致性； 3，选择圆和圆柱时，它们的轴线被用来进行约束； 4，选择球时，它的球心被用来约束； 5，有些情况下，可以允许存在过约束。 Digitized Shape Editor point line plane point3 translations2 translations1 translation line2 translations 2 translations and 2 rotations 1 translation and 1 rotation plane1 translation 1 translation and 1 rotation 1 translation and 2 rotations 各种几何配对之后所被约束的自由度 Align with constraints 约束法对齐 每一对约束元素都会自 动赋予一种颜色，且参 考元素呈透明色 ref1 ref2 ref3 单击“add”增加一对约束单击“add”增加一对约束 待移动对象 带移动元素的方向可以勾 选“manual”更改，但参考 元素的 方向不能更改。 Digitized Shape Editor Align with constraints 约束法对齐 对齐过程及结果评估： u约束的优先级，共分6级 uThe Statistics are given for the constraint elements, they do not refer to the real gaps between the Cloud to Align and the reference. Those gaps are given by the Distance Analysis. uA constraint with a Strict priority is not fully respected when the distance is greater than 0.001 or the angle is greater than 0.5. This may happen when a constraint with a Strict priority is applied simultaneously to other constraints. A message warns you that the constraint could not be fully respected. u对话框下方显示的统计结果是约束所用的几何元素之间的偏差 ，而不是点云之间的偏差。其中的距离偏差值是由“Distance Analysis”作出的结果。 u当某个“strict”级的约束没有得到严格的保证，即其距离偏差大于 0.001，角度偏差大于0.5度。发生这种情况很可能是另一个约束 也是“strict”级的，两者只能保其一。 注意：对齐的时候可以随时点击“Apply”观察偏差值，若发现大偏 差的时候，可以及时调整约束，删除或替换。 Digitized Shape Editor Align with RPS RPS法对齐 RPS法对齐与约束法对齐类似，也是使用了约束。但两者又有区别。其区别如下表： 约束的优先级，共分6级 关于RPS法对齐。由于RPS法对齐采用的是一种 静态均衡的对齐模式，即X轴，Y轴，Z轴三轴无 优先级差异，但必须满足下述条件： 对第一根轴，须冻结3个RPS点来定义一个平面 对第二根轴，须冻结2个RPS点来定义一条直线 对第三根轴，须冻结1个RPS点来定义一个点 在RPS法对齐中，最少需要3个RPS约束，最多可 定义6个RPS约束。 Align with RPSAlign with Constraints A well-defined RPS alignment must always be isostatic, to insure the repeatability of alignment conditions. Non-isostatic system is accepted. Constraints are defined only by points, circles and arcs. Constraints can also be defined by planes, cylinders and spheres. When a circle or an arc is input, its center position, i.e. a point, is taken into account When a circle or an arc is input, its center axis, i.e. a line, is taken into account Only translations can be frozen.Translations and rotations can be frozen. For each RPS constraint, at least one axis must be frozen. In a point - point constraint, you can freeze one, two or three axes of the point on the reference. In a point - point constraint, all the three axes (X, Y and Z) of the point on the reference are automatically frozen. Definition of a RPS Alignment Since a RPS alignment is isostatic, the following conditions must be satisfied: In a first axis, three RPS constraints must be frozen to define a plane. In a second axis, two RPS constraints must be frozen to define a line. In a third axis, one RPS constraint must be frozen to define the locating point. Defining a RPS alignment requires a minimum of 3 RPS constraints and a maximum of 6 R