datum dimension

基本解释

If the element being tested with tolerance requirements is an axis, centre line or symmetrical plane, the arrow and datum symbol should be aligned to the dimension line of that element.
当被测要素为轴线、中心线或对称平面时，指引线的箭头和基准符号应与该要素的尺寸线对齐。
This method realizes the 2 dimension constrained adjustment of GPS control network based on quasi-stable datum using classical adjustment of free networks and coordinate transformation method.
该方法采用经典自由网平差和坐标转换法实现基于拟稳基准的GPS控制网2维约束平差。
If the element being tested with a tolerance requirement is a contour line or surface, point the arrow and datum symbol to the contour line or surface, and keep it away from the dimension line.
当具有公差要求的被测要素为线或平面时，将指引线箭头和基准符号指在线或平面上，且必须与尺寸线错开。