Two questions about 'Create Alignment From Object'

[jeff_rivers]

I'm attempting to create an alignment from a polyline I just drew.  I'm struggling with how C3D decides to create the alignment's direction.

That is, I picked a starting point then an ending point for my polyline, and I want the alignment 0+00 beginning station to be at that same starting point from drawing my polyline.  

First, when I get to the step where I'm prompted "Press enter to select alignment direction (or Reverse)", I do not see the direction arrow cue on the alignment.  

I've seen this happen off-and-on in the past.  What controls whether that arrow cue appears?  I thought it was related to Layer zero being on/off, so I made sure it was on before attempting to create the alignment.

Second, it is not using the first point of my polyline as the beginning of the alignment, it is using the last point as the beginning, so my alignment stationing is reversed.  And because the arrow cue doesn't appear, I don't realize that until too late (profiles created, profile view, etc).  

tl;dr: What controls the visibility of the alignment direction arrow when creating an alignment from object?  What determines which endpoint C3D uses to be 0+00 station when creating alignment from object? 

[Jeff_M]

The only time I've not seen the direction arrow is if it is off-screen due to zoom level, so not sure what controls that. The direction is controlled by where you pick to select the object, the start will always be the point (start or end) of the polyline closest to the pick point.

[jmayo-EE]

I agree with Jeff's post.

Try this, make a pline on a layer other than zero. Turn layer zero off and zoo to the full extent of the pline. Create the alg and you will see the arrow with layer 0 off.

Undo and zoom in real close to one part of the alg and  recreate it, the arrow is not seen. Zoom out a bit and still not seen.

Now the big tip...While still in the command, zoom to the full alg extents and right click. The arrow appears with the prompt to change direction.

[jmayo-EE]

https://autode.sk/3kxcGMi

[jeff_rivers]

Quote: "The direction is controlled by where you pick to select the object, the start will always be the point (start or end) of the polyline closest to the pick point."

Wow, thanks Jeff!  So simple, yet I never figured this out!  

[jeff_rivers]

I have wondered if the object being partly off-screen because of the zoom level had something to do with this, but if I zoom out, nothing ever changed, the arrow never appeared.  I'll try again, this time right-clicking after zooming out.  

[Joe-Bouza]

Hi Jeff 

sorry for asking this but why draw a polyline to create an alignment?  You can use the same steps directly drawing the alignment tools and then some.

[lim.wendy]

Hi @jeff_rivers,

I've similar observation as @Jeff_M, let me know if you want me to check with the Product Team. Sounds like a good idea to have it documented. 

[AllenJessup]

Joe,

There are two reasons I might create an Alignment from a Polyline. The first is I get drawing from consultants that have polylines for alignments. The other is that sometimes I find it easier to tray some different scenarios with Lines or Polylines and then select the final one and convert it to an Alignment.

You have to check the accuracy. Especially in the first case.

[jeff_rivers]

Same.  Type PL, <enter>, sketch out an idea for an alignment.  If it works, then turn it into an alignment.  If not, erase and do over.   Quick and easy. 

Often my alignments are short, and not on the main corridor baseline, they are just so I can cut a profile to see if I have enough cover or the slopes have the grade I need, or so I can check for interference with underground & overhead utilities.  

Here's a fun example: I need four profiles.  They run from the centers of the proposed traffic signal poles, making a large box that encloses a signalized intersection.  I want them to start and end ten feet beyond each pole.  The pole symbol is a block with an insert point defined at its center.  

Draw a pline from insert to insert, starting at one pole, ending at the pole across the intersection.  Repeat three more times.  Draw a 10' radius circle centered on each pole.  Extend the polylines to the circles.  Now my polylines begin and end ten feet past each pole.  Turn them into alignments, create surface profiles and views, and now I have profiles showing all the proposed poles, and each profile extends ten feet beyond each pole so I can see what's going on behind the poles.  

[AllenJessup]

@jeff_rivers 

Nice example.

I often draw an alignment with lines and arcs. Draw a line then start an Arc command. When asked to "Specify first point" hit enter and the arc is automatically tangent to the line. After drawing the arc start a line and hit enter. The line is tangent to the arc. When I'm close to what I want. I Join the arcs and lines and create an Alignment from the polyline.

Then I can fine tune the alignment.