Using Construction Lines

The Purpose of Construction Lines

Construction lines are not always essential but they can be used to create a 3D framework to assist with the creation of a complex 3D design. They effectively mark positions in the 3D environment. These marked positions can be used as a datum for relative object positioning. They do not affect the actual objects of the design but are simply used as a convenience tool.

It is perfectly feasible to create designs in the 3D view using world coordinates only (i.e. always using the world origin as the datum). However what generally matters in a design is not the world position of the objects, but their relative positioning in the overall design. Often the parts themselves are adequate for marking positions, for example everything in a design could be created relative to the position of one end of an object. However in more complex designs this may become inadequate, particularly since the matching operations can sometimes make minor adjustments to object center line positions in order to achieve a match with another object.

Generally when creating designs of more than 2 or 3 objects it is better to create a construction line framework first. Such a framework could consist of any number of construction lines in any 3D orientation but it would normally consist of a number of construction lines each lying oriented along one of the cartesian axes. A relative 3D position can therefore be located using 3 construction lines, one lying in each of the X, Y and Z cartesian axes.

Fig: Construction Line Example

Given this kind of framework the position of a second part could be achieved easily by linking it to the end of the third construction line. The following example shows it used to locate the second end of a part normally, and then used to locate the second end of a part with the end face facing vertically and obliquely skewed (using Oblique Activate) to connect with the end of the construction line.

Fig: Object Positioning Using Construction Lines (Normal and Oblique)

The construction lines of a design would also normally tend to be linked into the same framework unless the design is deliberately constructed in more than one part. Then as parts are dragged around all the linked parts move together and maintain their relative position (note: to drag parts seperately they have to be unlinked).

Reporting to Transcript

The reporting facilities are useful for listing the length and position of construction lines. Also the measurement tool is very useful for measuring relative positioning.

Creating Construction Lines

See: Creating a Construction Line

These techniques, using construction lines for achieving and maintaining 3D relative position of objects are a powerful and important facility when creating complex designs using the 3D CAD designer. For example they can be used to create designs such as the following diverter intersection: