Triangulate using control strings
This function allows you to triangulate between segments using control strings to provide definition to the triangulation process.
Note: The control strings must exist before this function is invoked.
Control strings can be created using the GRAPHICSDigitising functions. Digitise a control string by selecting one point on each segment which is to be triangulated.
Note: You can use between 2 and 10 control strings.
In the triangulation process the control string will act as a breakline, and triangles will not form across it. In order for the 3DM to be created correctly, control strings should not cross each other. The starting points of the segments from which the 3DM are created also define control. Therefore control strings should not be digitised across the segment starting points.
The first control string, known as the master control string, must connect together all the segments which are to be triangulated. Second and subsequent Control strings do not have to connect all the segments from which the 3DM is to be formed. Control strings can be limited in length so that they join only the segments which require control to create the 3DM correctly.
It is important that you understand how the control strings are used. The control strings are simply string segments which consist of at least two points but typically more than two. They are created by selecting points on the segments which are to be triangulated. When the triangulation is about to commence, all other strings in memory, excluding those selected as control strings, are searched to find points which are exactly coincident with the points on the control segment. The segments containing these coincident points are then used for the triangulation process.
Note: To form the 3DM, control strings must be selected in the order that they are to be applied.
For this reason, it is a good idea to number the control strings as sequential string numbers.
When you have finished digitising the first control string in Digitising choose Next String to increment the string number by one.
Select a point to define control segment 1
Position the pointer and select a point on the first control string.
Selecting a point on the first control string will display the prompt:
Select a point to define control segment 2
Position the pointer and select a point on the second control string.
Selecting a point on the second control string will display the prompt:
Select a point to define control segment 3
Continue to select the control strings until all control strings have been selected. Once the last control string has been selected, cancel the prompt:
Select a point to define control segment x
by pressing the Escape key.
Note: Up to ten control strings may be defined at any one time.
The control strings may be defined in any order although the first one which is selected - the MASTER CONTROL STRING - must connect together all the segments which are to be triangulated.
You must use at least two control strings.
Once all control strings have been selected, press the Escape key to cancel the prompt and display the DEFINE THE TRISOLATION TO BE CREATED form.
Function
Display only. The name of the function being executed.
Layer name
Display only. The name of the active layer is displayed. The active layer is the only layer you are able to modify.
Object
Enter the object number of the 3DM to be created.
Trisolation
Enter the trisolation number of the 3DM to be created
Result
Complete the DEFINE THE TRISOLATION TO BE CREATED form and choose Apply to create the 3DM and to update the screen picture.
Warning
The point selected is not in the working area and cannot be edited
You may only create 3DMs from strings which are in the active layer. You have selected a segment which is not in the active layer.
String xxx segment yyy already selected as a control segment
The string and segment number shown has already been selected as a control segment. It makes no sense to select it a second time.
The number of control points exceeds the first selected segment
This is another validation test to ensure that the 2nd and subsequent control strings only connect together segments connected together by the MASTER control string. This message indicates that there are more points in the most recently selected control string than there are in the MASTER CONTROL STRING. The control string in question is incorrect, check for either:
- duplicate points in the control string, that is, connected to the same segment more than once, or
- connected to segments which are not connected by the MASTER CONTROL SEGMENT.
Segments to be triangulated are inconsistent
They must all be open or closed.
The segments connected by the MASTER CONTROL STRING must all be either open or closed. It is not allowed to have a combination of open and closed segments connected for triangulation.
No segment found which matches control string xxx segment yyy
The identified control string has a point in it which is not connected to any other string. You can find this easily by plotting the markers for this segment and finding the point which does not touch any other string.
No segment found which matches control String xxx segment yyy in master control segment.
This error means that the control string xxx segment yyy touches a segment (which is to be triangulated) which is not touched by the master control string. This is not allowed. The master control string defines all the segments which are to be triangulated and all the other control strings must only connect to these segments.