Surface / Curve > Union (A=A+B) (Trim Menu)

Using this command existing flat objects can be combined into one surface which covers all areas of the drawing which were covered by at least one of the surfaces. This is the same as creating a union of two surfaces according to group theory.

The following object types are classed as "flat": circles, circle sectors, circle segments, ellipses, ellipse sectors, ellipse segments and surfaces. Ellipses and ellipse parts are converted into polygons and are therefore "only" contained as polygons in the result.

In this command's parameters, you can choose whether the result shall be automatically simplified (see "Simplify Curve / Surface" dialog), and set the corresponding tolerances.

The result in each case is one "surface" object, which may however be made up of more than one surface part. A graphic with examples of the union follows:

The order in which the objects were identified does not influence the result. The resulting object will contain all attributes of the two chosen objects without duplicates.

This command works with all objects which have a closed outline. These are automatically converted to surfaces for the calculation. Many object types can not be converted into a surface without loss. Ellipses and ellipse parts must be converted into polylines, which invariably leads to a loss of quality. The precision of the conversion can be specified using the command Drawing Settings > Precision in the entry "Transform". The original objects (which remain unchanged if the duplicate function is active), are not influenced by this conversion. Surfaces with "holes" can also be used. There can be problems if both objects share (part) of an edge. In this case there can, in spite of calculation to 16 decimal places, be incorrect interpretations. Do not rely on overlapping surfaces always or never being combined. This varies from case to case. The result may consist of one object which contains both the original surfaces, unaltered, as part surfaces.