Best Practice Building Surfaces

[Anonymous]

All,

When building surfaces I typically attach survey figures first, then add a point group second. The point group i use excludes the point descriptions that create the breaklines. I recently had a disscussion with a coworker that thinks this is not the way to go. I am curious how others do this.

[jmayo-EE]

If you add the points that create the breaklines and add the breaklines your surface has redundant data and I am pretty sure you will have surface errors/warnings at each redundant node.

We typically add the non-break points first then the figures.

[ericcollins6932]

IMHO it shouldn't matter as breakline points are still ground points, although you might get duplicate records if you bring them in twice.

I would bring them in as another point group, but still be a part of ground points, just so I can differentiate them from regular ground shots.

[BrianHailey]

There's absolutely nothing wrong with either method. If the point is exactly the same as the breakline vertex, the surface treats that as a single point (exact same x,y,z is just one point).

Breaklines With Points

• Pros
  Don't have to exclude the points from the point group
• Cons
  If the breakline moves, the point must be moved too

Breaklines Without Points

• Pros
  Only one datasource for the surface point so only one thing to edit
• Cons
  You must exclude the points used to create the breaklines from the point group

[troma]

Our surveyors have started to shoot everything as breaklines. Random spot heights in an open field?...you end up with a boustrophedonic breakline over the whole field. I don't think they put any points in the surface anymore, just build it from breaklines alone.

[fcernst]

Best practice is to attach points first and figures/breaklines after that. Make sure the figure/breaklines stay after the points in the build order.

Keep those figure/breakline Points in the topo drawing for your engineer to be able to reference to help figure out the existing ground's story during his/her design process, but don't use them to build the EG surface.

If the figure/breakline moves and the survey tech is not diligent about moving the points subsequently, then you have a big mess on your hands.

[BrianHailey]

---

@troma wrote:
Our surveyors have started to shoot everything as breaklines. Random spot heights in an open field?...you end up with a boustrophedonic breakline over the whole field. I don't think they put any points in the surface anymore, just build it from breaklines alone.

---

That's asking for trouble in my opinion. Breaklines should be used when necessary and not haphazardly across the entire surface.

[jmayo-EE]

Let me try to subtract that con. 🙂

If this is field data the breakline points should not have to be removed. This should be done automaitcally via desc keys and point group  and surface data management.

[troma]

I understand that they aren't necessary except where the ground is actually breaking, but what's wrong with what they're doing?  I guess the only pitfall I can see is if they loose track of what they're doing and end up with crossing breaklines, but I don't see that as being too hard to avoid or to fix.

Anyway, it's not my decision and not my problem; but I appreciate any advice and education regardless of whether I have a use for it.

[csevers]

Agreed, get as many points as possible, then put in breaklines where necessary.

[Anonymous]

boustrophedonic  

Web definitions

of or relating to writing alternate lines in opposite directions.

[Anonymous]

Thanks for all the insight, its interesting that so many different methods are around.

[troma]

---

@dmartin wrote:

boustrophedonic  

Web definitions

of or relating to writing alternate lines in opposite directions.

---

I learned that word in another post on these forums dealing with cogo points.

[Joe-Bouza]

All sounds good, but I'm pretty sure the BP white paper recommends adding point from file to surface not the cogo points

[jmayo-EE]

I think that is BP for large data sets due to [erformance issues with a large number of points.

[ericcollins6932]

If surveyors are shooting everything as breaklines, then they do not understand the concept of breaklines in a TIN.

As one should know, a breakline prevents TIN lines from crossing it - and essentially defines an edge (or grade break).

Points in an open field shouldn't be breaklined unless there is a very good reason.

[troma]

I guess the theory is that they are shooting a regular boustrophedonic grid pattern anyway. They do it in straight lines to form a grid with roughly the same x and y values. So none of the points on one line should triangulate past the next line anyway. The resulting TIN will be identical no matter if the data is added as points or breaklines.

I'm not saying this method is best practice, but it's what they've decided to do for now. I understand that theoretically these points shouldn't be used as breaklines, but in reality there is no adverse affect on the surface. The TIN is identical.

[mathewkol]

One more thing...

If youo're going to use Proximity breaklines, you need to add points first or there will be no TIN lines to swap because of the breaklines.

[sboon]

Peter Funk has addressed this question previously, from an efficiency perspective.  If points are added first, then the software will triangulate between them.  Breaklines added after the fact means that some of the TIN lines have to be deleted, then the breaklines added and then the rest of the triangulation redone. 

Breaklines first, then points is more efficient and faster for processing.

Steve
Please use the Accept as Solution or Kudo buttons when appropriate

[wfberry]

Steve (I don't care if it is -20 F, a tee shirt is perfect):

If a breakline is added "after the fact", tin lines will automatically triangulate to the nodes on the breakline.  I don't recall it not working that way.  Am I wrong?

Bill