Existing grade, proposed grade, breaklines, and volume surface

[Anonymous]

I have no one in my company to go to with questions like this so I apologize in advance for what may be stupid questions. 

I have a survey file that includes contour lines and a property boundary. We need to "smooth out" the land in a few places. I have drawn proposed grading lines where needed and where diversion ditches, sediment basins, and a road are needed. What are/where do I need breaklines? I created a surface for the existing grade and a separate surface for the proposed grade but the proposed grade looks wrong (lots of added lines). Are breaklines the only thing I'm missing/doing wrong? Any advice you can give will be much appreciated! 

[Anonymous]

You've got something wacked with your proposed surface data. Use 3DORBIT to spin the model around in 3D and you'll see what I mean.

Anytime you got a super close contour interval - short distance between contours - I would suspect something is wrong. Looking at it in 3D can help identify the problems. You may want to edit your surface style, or create a new style, to show just the triangles so that you can precisely identify the suspect data. I draw a temporary line from a bad point to 0,0 or out into space so that when I go back to plan/top view I know what point is bad.

A breakline is a line that the triangles, or TIN, are not allowed to cross. Imagine a ditch with a survey shot on both top of banks opposite each other. You do not want the TIN to go between these two shots because then it ignores the fact that it drops down into a ditch n between the two banks. A breakline along the tops of banks (and toes of slopes, and center of ditch, etc. etc.)  will prevent the TIN from connecting these two top of bank shots and correctly force it down into the ditch.

Typical places to use a breakline would be vertical breaks, like top/toe of slope, in the bottom of a V shaped ditch, and along any hard edged surface, like sidewalk edges and curb & gutter (top of curb, face of curb, flow line of curb, flange line of curb - if you wanted to model the whole thing), etc.  - anywhere there should be a straight line between points. CL of road is another. If I go wild with breaklines I end up a 3D wireframe model of the entire surface with data points in the open areas to supplement the breaklines.

I always spin it in 3D using 3DORBIT to check.

hth

[lynn_zhang]

Hello @Anonymous ,

Just checking to see if your problem has been solved. Did the response from @Anonymous help answer your questions? If yes, please click on the "Accept as Solution" button in his reply so this helps other users in the community find the solution too. Thanks!

[Anonymous]

Eturner,

I see a few things when I looked into your drawing.  

1. there are polylines at elevation zero that you included in your contour data that are causing the excessive contour lines.   they appear to be maybe silt fence or a drainage line.  one of them is actually on the contour layer but doesn't make any sense.  it's likely that line should have been on the same layer as the other lines at zero elevation.

2. Even once the zero polylines are corrected, there are several contour lines that cross each other and add confusion to the surface.  It almost seems like you are adding two propose sets of contours for different surfaces all into the same surface.

3. The contour line surrounding the small pond in the se corner goes from 115 to 115.5 and you can't have this when adding contour lines to a surface.  If you want differing elevation along a line, try using a feature line instead and adding it as a breakline.

4. it helps alot to keep contour information which is surface information on a different layer than it will be once part of a surface display.

I hope this helps you.   Please ask any specific questions you may have.