CHAIN

Purpose:

To enable a user to create a geometric chain of adjacent elements, particularly line, arc, spline, polyline, and contour elements, such that the resulting chain can be manipulated as a single continuous element. This function will also enable the user to create a chain formed from two or more chains.

Prerequisites:

The user must ensure that the geometric elements either connect at their end points with the required adjacent elements in the anticipated chain or that their respective adjacent ends are within the established dimensional tolerance, (see Options below). This function does not recognize elements that do not either share end points or have end points that are separated by a distance that exceeds the set tolerance. However gaps are allowed between the extreme start and end points in the final chain, that means, the chain does not need to form a closed loop.

Instructions:

1. In the Tools menu, click Chain.

2. Cursor-select any geometric element that is to become part of the chain. The system responds by drawing one, two or three rectangular boxes around all the graphic entities in the region, according to the previously established subpicture levels. If the user wishes to operate only on the information at a specific level then he will need to use the Appropriate function in order to display only the graphic information on that level. All items within the box or boxes are high-lighted and the user must then click the OK button if he wishes to continue with chaining operations.

3. Cursor-select a starting or ending element in the intended chain, and which can be either a line, an arc, a spline, or a contour, The system needs directional information in order to build-up the chain from the connecting elements and hence the user should make the initial cursor selection close to one of the points that will become either the start point or the end point of the chain. The direction along the element, and resulting chain, is determined from the nearest end point on the selected element to the cursor position.

4. The system responds by high-lighting the selected element, the connecting elements that it finds that will form the chain, and displaying temporary small circles around the terminal end points of the overall chain. If the selection and ensuing chaining is the one that was intended, then the user must click the Yes button in the displayed simple dialog box.

5. If the displayed end point is not the one that the user intended, and, generally, it is at a location before the expected end, then the user will need to examine the connection between the two elements that otherwise appear to connect together. This can be done by using the Zoom Up function. If the respective end points of the two elements are not coincident within the pre-set tolerance then the system cannot connect the two elements together in order to continue with the chaining operation.

6. If more than two elements connect at an end point, or within the tolerance level, within the length of the intended chain, then the system will stop the chaining at the branch point and require input from the user as to which one of the two, or more, elements that it should then chain along. That is to say that the system does not know which path to take when it reaches a branch point. The system displays the optional elements leading from the branch point and the user must cursor-select the required one.

Options:

There are no options within this function.

However a user can allow for elements in a required chain that do not actually connect, that means, the chain does not need to be continuous, by changing the tolerance setting. The tolerance can be changed through the Format > Defaults function.

Result:

A chain of geometric elements is created within the graphic display and the associated drawing file, and this can then be treated by the user as a single entity in future operations and manipulations. An element that is made part of a chain cannot be individually manipulated nor deleted as long as it is defined as part of a chain