3d alignment and sampling

[Anonymous]

Gents,

Could you guide me in the right direction?

I have few cl spot shots with elev and dirt shots located along  the road.  I would like to create 3d line that I would then convert it to alignment in order to sample it and create profiles crossections. How do I run the alignment(3Dline) if the shots do not line up? DO I want to go to terrain/3dpolyline/create by elevation? but if ponits dont line up I can't.Does the alignment has to be tangent or no? I'm using ldd 2004 with civil design.What would be the most efficient way?

Thank you!

[Anonymous]

You can have the alignment go any way you want but it all depends on the work you are doing.  If you are doing a road improvement project, normally the alignment would run along the centerline of the proposed road right of way, since this is used for control.  But if this is not, think of the control that would be needed if you are removing and replacing the asphalt along said road for staking purposes.

[Anonymous]

Sounds to me like you're trying to do too much with too little.  how many is "a few cl shots", and do you have anything past the edge of road?

The 1st thing you start with is a surface - that's what the points with elevation are for.  If you don't have anything past the edge of road your surface is going to be inadaquite, and that will result in bad cross sections later.

I'm confused by your reference to "tangent".  Are there curves in this road?

If the cl shots are close to the real center of the road, your alignment can be defined by using a line or polyline that best fits the mean of the shots.  Alignments are an arbitrary thing.  They are chosen for their ability to help you define a construction zone.

Reid

[Anonymous]

Reid,

Thank you for your reply. I have enough topo shots past the edge of the road to generate surface and enough along the more less cl.  I like the idea of best fit line as it uses least sq method, but

-how do I assign/interpolate elevation if I use best fit line or just a polyline?

-yes, there is curves in the road, (road has very irregular shape with delapitated asphalt or gravel), My question was when I draw alignment if the curve has to be tangent.  

[Anonymous]

Usually it is, but it doesn't have to be.  It will look "goofy" if it's not.

The alignment has no verticle information associated with it.  It's just a plan view at 0 elevation.  The profile is where your verticle information is represennted.  The combination of the alignment with the surface is what generates the profile (existing ground).

Reid

[Anonymous]

Reid,

I don't quite understand. I might be wrong, but I always thought that  

in order to sample from surface I need to have alignment defined.If my alignment  will be at EL=0 and my topo shots will be at 900' it will sample from 0 to 900. Alignment has to be 3d line, am I right or no?  

[Anonymous · Accepted solution]

No, the alignment is not a 3d entity.  It is defined though.  I usually use regular lines & arcs to define an alignment.

The program will sample the length of the alignment using the upper & lower limits of the surface.  If your surface low point is 890.00 & your high point is 936.76, those are the values used.  Make sure your alignment stays inside the boundary of the surface, or you'll get a drop to zero in the profile.

Another thing I do with alignments is start them with a value of 1+00.00.  This will usually prevent any negative stationing if the begining of the alignment is edited.  I also like to start & end an alignment few feet past the end of improvements (if I have enough surface data to do so).  It's a style thing - I just think it looks nicer with a bit of existing ground past the improvments in the profile.

Reid

[Anonymous · Accepted solution]

Thanks Reid.

Greatly appreciate it!!