Tailoring Triangulation

Very useful tool - indispensible in fact.

To respond to your immediate problem, I would point out that what you get is not a 'void' in the triangulation, but that you get 'null triangles' (if I recall correctly trimming a triangulation using the linemode options works the same way).  This means that when you come to create contours, it won't contour those triangles. So the effective 'void' is in the contour model.

It's important to ensure that the PBRK string is as close as practicable to the model feature you actually want to to be the limit. The point interval should be no greater than that of the relevant feature string.  So take for example a roundabout island where you don't want to contour within the kerb line: create a parallel string, offset say 15mm inside the circle of the kerb line. 

Further notes that might be helpful:

• It's the points of the PBRK string that matter, not the string itself. So the one PBRK string can jump around doing its magic at various places.
• You can create a 'library' or 'resource' model in which you store various strings that could be useful as PBRK strings. If they are stored with your conventional labelling for temporary strings (for me that's x y or z, or mx my mz etc), then you can copy into your model (which is to be triangulated), rename as PBRK, run the triangulation, then delete the PBRK string. You can even assemble a new PBRK string from various ones stored in your library model, using EDIT 008 or 012. If you use input files generally for design, you can generate the strings in the library automatically, and thus they will adapt to any changes in the design.
• In simpler cases it may be more efficient to not bother with PBRK, but create a boundary string (previous bullet point applies for those too!) and use that to trim the contour model: but that get's complicated and time-consuming (even in input files) if you've got more than one or two 'voids' to create.

Hope this is helpful - have fun. Let me know how you get on.

I can just highlight what can going wrong with pbrk.

1- All levels must be -999

2- It is not used as a boundary. In fact all triangles that are built on a point of the PBRK are removed. So if you want to make a void in the triangulation you have to:

• create the boundary of the void
• copy the strings out of the boundary to another model
•  As well explained, offset the boundary by 15mm inside, maybe add additional points to prevent triangle to be created in unexpected area (remember PBRK is a P string so no link between points) and rename it as PBRK.
• Triangulate the model

Hope this could help you

Palan

 PBRK is a good option to tailor a traigulation or to create void region in any DTM...but you can not have more than one PBRK in  model so it limits you......

I can put another solution for you...may I!

Just tack on the below points of mine

1. create strings of void region in the model u want to traingulate
2. create bonadary arround this model using modify option
3. go into the trimming tool and set the REMOVE TRIANGLES as CROSSING (use drop down)
4. now drag the cross hair in the void region strings that you created earlier
5. then click on close and give the bonadary name
6. once you saved the bounadary you will see a spider web like string of boundary
7. now go to the ANALYSIS option and use Triangulation from String Model option
8. Provide the model name, boundary details and then go to triming details
9. Toggle on TRIM TO A BOUNDARY and then go for bonadary string name again
10. Now appy the option, you will see the tailored triangulation as desired.....!

Hope the above works for you...if not...i'll elabore more

Cheers & Respect

Irfan

"PBRK is a good option to tailor a traigulation or to create void region in any DTM...but you can not have more than one PBRK in model so it limits you...... "

 I just want to point out that as the PBRK string is a Point string, you do not need to have more than one string. The PBRK string can have as many points in it as you need, at any areas of the model they are needed

If you had three traffic islands (for example), create temporary strings - offset from the actual string in the model but with null (-999) levels. Join these 3 temp strings into one PBRK string, and you would have 3 voids in the triangulation. 

Mark

Hi I am new to MX and am having exactly the same problem - trying to trim a region within a triangulation. Could anyone show me a more detail procedure of how to use PBRK string to trim a triangulation please?  If it can be done using the commands of input file as well would be of great help. Thanks a lot.

Cedric