Breaklines

Breaklines are pretty important/useful for all topos. They let you decide in the field how the surface gets built, where the slopes, vertical faces, curbs, ditches, ridges, etc., are.

I can't imagine topo-ing/contouring without using them.

I use breaklines for almost every point in a topo, excepting grid shots on uniform surfaces. DTM/Contouring software generally does fine on a channel with cross-section shots, so long as the cross-sections line up extremely well. If they don't line up, and no breaklines are defined, the triangulation lines will likely connect from top bank to top bank, across the flowline, producing an incorrect DTM. Even in the case of proper cross-sectioning, any shots made to other topographic points, such as a power pole half way up a ditch bank, that aren't lined up with a collected cross-section can connect across the flowline or to the edge of pavement on the other side of the road and produce an incorrect model. I see it frequently in topographic surveys produced by others an in some of our older work before we implemented breaklines.

Topographic surveying with breaklines also forces the crew in the field to be more thorough in collection, thinking out the way the software will connect the dots and making sure that features are thoroughly mapped, which I believe increases field efficiency as a result. Often times in a complex area, the temptation is to simply gather more random shots and hope the software will make sense out of it all. With more complex topography, more shots are necessary, but having a plan, taking each element piece by piece takes wishful thinking out of the equation, creates a system in which each collected point has a purpose and produces a more accurate picture of the surface.

I agree with the posts above. I use breaklines for everything. Curb, pavement, centerline/crown of road, top of bank, toe of bank, buildings, concrete, you name it...

> I can see how breaklines would fix a TIN surface in the case of a ridgeline or at a retaining wall, but would it also be desirable to put breaklines at such places as a Top of Channel or Toe of Channel, or the Flow Line of a Wash?

Using breaklines will reduce the number of shots - and the amount of editing - you need to correctly model a site even when the break isn't sharply defined. In those cases where the "break" is more of a "roll" it never hurts, and often helps, to use breaklines. So if in doubt, err on the side of using more breaklines.

> I agree with the posts above. I use breaklines for everything. Curb, pavement, centerline/crown of road, top of bank, toe of bank, buildings, concrete, you name it...

Yup! That way you know the triangle edges are where they're supposed to be. I would hate to have to check every triangle, especially when I often have over 100,000 of them.

right on.

I my book, break lines are manditory. Like Mr. Oklahoma said, the more the better. Wildsoft use to have multiple break line styles. The difference being on how rigidly they held the break. The resulting DTMs were by far nicer than what comes out of modern CAD packages.

I agree with Shawn. I hate using spot shots, and then spending time in the office telling the computer what I meant. Or worse, it gets processed by someone else, then who knows?

Thanks, everybody. I guess that answers my question. More is better.

Dave

Aside from creating a better tin, they are also helpful if the person processing the data was not the person in the field. When I have a picture drawn by the crew, there is less of a chance of me interpreting shots incorrectly.

In LDD you can also offset a breakline with an elevation difference, for curbing say, saving you having to shoot top AND bottom of curb in the field, again saving time.

-V

An easy to remember rule is that if you feel it as you walk over it then treat it as a break line. Thus breaks of slope and distinct rollovers will register, anything solid; and you would probably notice the change in slope as you walk over the crown of a road.

As others have commented, try and view the ground as you walk and picture the contours - if they change direction sharply then put in a break line.

It all speeds things up back in the office and avoids getting the wrong shape. Bear in mind that freestanding walls often have some build up of ground on one side and may need a break line along the back - the same applies to hedge lines where commonly the line of the hedge root can be quite raised relative to the adjacent ground (which has been eroded by the passage of many feet/hooves.

Make sure they're in 3D....;-)

Good thread

Here is a screen shot of a t-net with no breaklines used.

Notice the skinny triangles and how they cross the bottom of the draw.

Here is how it looks in 3D

You can see how it has modeled across the f/l of the draw. This was with shots taken every 50' +-

Now with the use of breakline and a proper inclusion boundary, this is what you get in 2D

Notice how the f/l of the draw is clearly defined.

Now you could take perfectly aligned shots every 10 along the feature (not using breaklines) and get something that looks like this..

Question is, do you want to take 41 shots or 282 shots? Saturating your mapping with un-necessary data, leads to confusion and mistakes. More is not necessarily better.

If you gather your data properly in the field using breaklines, the creation of the surface can take minutes with no editing.

> I use breaklines for almost every point in a topo, excepting grid shots on uniform surfaces. DTM/Contouring software generally does fine on a channel with cross-section shots, so long as the cross-sections line up extremely well. If they don't line up, and no breaklines are defined, the triangulation lines will likely connect from top bank to top bank, across the flowline, producing an incorrect DTM. Even in the case of proper cross-sectioning, any shots made to other topographic points, such as a power pole half way up a ditch bank, that aren't lined up with a collected cross-section can connect across the flowline or to the edge of pavement on the other side of the road and produce an incorrect model. I see it frequently in topographic surveys produced by others an in some of our older work before we implemented breaklines.
>
> Topographic surveying with breaklines also forces the crew in the field to be more thorough in collection, thinking out the way the software will connect the dots and making sure that features are thoroughly mapped, which I believe increases field efficiency as a result. Often times in a complex area, the temptation is to simply gather more random shots and hope the software will make sense out of it all. With more complex topography, more shots are necessary, but having a plan, taking each element piece by piece takes wishful thinking out of the equation, creates a system in which each collected point has a purpose and produces a more accurate picture of the surface.

The rod person must be knowledgeable of how a surface is created and in my opinion is the most important person in the process of creating the dtm. Just my 0.02'

That's cool, imaudigger! Thanks!

Dave

Very well done!
Chr.

>> More is not necessarily better.
:good:
But a picture is worth a thousand words. Very well done. Will show this to my kids I am training in the field and office.

well done.