In my overview post describing the alignment enhancements in AutoCAD Civil 3D 2012, I talked a little about some new options when importing alignment geometry via LandXML. These new options were put into place to allow alignments to maintain fixed, free, and floating tangency constraints. Let’s take a look at how each of the three options mentioned work after the jump.
As I mentioned, there are three new options for importing alignments via LandXML. To recap:
- Fixed only – this replicates the current functionality where all alignment elements are fixed.
- Floating off first element – this option assigns a fixed constraint to the first element and all subsequent elements are assigned a float constraint.
- Free and floating curve groups – this option attempts to identify supported free curve groups and floating curve groups and then assigns constraints accordingly.
To illustrate this, let’s take a look at my test data – I have created an alignment with curves and exported it to LandXML. This is how it appeared originally in the drawing:
For the sake of editing, I am going to focus on the first curve (my alignment stationing begins on the left, so I’m looking at the first small curve to the south.)
Now, where do you set these options? They can be found in the Edit LandXML Settings dialog. This is located by navigating to the Settings tab of Toolspace and right-clicking the drawing name, then selecting Edit LandXML Settings. The very last option on the Import tab will be Alignment Import Settings, as seen below:
It should be noted that this option defaults to free and floating curve groups, which happens to be my personal favorite. Let’s take a look at the edit behavior of a curve when imported with this setting. Again, I am editing this curve simply with grips and pulling the curve out, as shown below:
As you can see below, the curve is now shorter and all tangencies are maintained:
Next, I will import the alignment using the fixed only option in the LandXML settings. Once the alignment is imported, I will perform the exact same type of grip edit shown above:
Even the most casual observer can see the difference – the tangents remain fixed while the curve changes, which throws things all out of sync.
Bonus – if you look carefully at the above image, you will notice two warning triangles. These are the new tangency design criteria checks that I mentioned in my overview post!
The very last option to explore is floating off first element. This one struck me as a little strange. Keep in mind that I’m performing the same edit on this one as well:
See, this where things get wacky – the first element (tangent) is fixed. It’s not moving. But everything thereafter hinges on that tangency point and floats from there – the whole alignment now remains tangent at that first tangency point and pivots around as tangency is maintained. Personally, I don’t get it, but I’m sure it’s there for a reason – if you find yourself using this one, kindly comment and let me know why. You won’t win a prize other than a deep feeling of self-satisfaction for satisfying my curiosity.