View Full Version : basic alignment tools
2009-05-07, 02:14 AM
Can someone explain why i can't use the majority of the alignment tools? The only tools that work are one that are "between entities". For example, i want to add the free compound spiral line spiral between two curves but when i select the two consecutive curves in my alignment it says "cannot attach an entity to a free entity". If the "free entities" are just for design drafting purposes similar to LDD, then how do i add them to my alignment after i've created them?
2009-05-07, 02:20 PM
The issue that you are running into is that you cannot attach 2 free entities together. Free entities are formed based on the parameters of the entity before and after. Floating entities are based on parameters of one or the other, and fixed are based on their own parameters. A good example is a basic horizontal curve between 2 tangents.
A free curve recalculates every time you change either of the tangents.
A floating curve only recalculates when you move the tangent it is based off of.
A fixed curve only recalculates when you grip edit or change the curve itself.
Hope this helps.
2009-05-07, 04:39 PM
So is it safe to assume that if i want to take advantage of C3D's dynamic capabilities, I will always use "free" entities?
A "Free" entity takes most of its parameters from the objects on either side of it, so you can only use Free entities between other entities.
A "Floating" entity has a firm connection to the entity on one side, but a "free" connection on the other side.
Otherwise, you have a specific curve, which you must define in some way, such as by picking three points.
You use the correct entity that is appropriate for the type of geometry you are trying to create. An Alignment may use all three types in different places.
2009-05-07, 08:05 PM
but if you had a tangent section then a floating curve attached to it followed by a tangent, if the second tangent changes you've just introduced a horizontal deflection at the end of your curve. Why would you ever want that?
2009-05-08, 04:28 PM
It all depends on what your are trying to do. Typically my curves are free curves, but, if you're at the end of an alingment, you must use a fixed or floating curve. If your curve is not between 2 tangents, what object do you want to hold and what object do you want to be "free". Its all about techniques and knowing what your tools are.
If you were designing a simple road alignment with tangents and curves, no spirals, reverse curbs, superelevation, then I would create fixed tangents and free curves, but if you get more complex, the techniques change.
The same goes for building a profile from layout.
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