Different Elvations

[BrianD17]

Just created an existing grades (eg) surface from a survey.  When I hover near a spot elevation from the survey of 830.31 I get an eg reading of 830.011.  In other places they are the same or very close, others not.  I'm not sure which number to go with, the one from the survey or the one from the surface created from the survey.  Have i done something wrong when i set the surface up?

Thanks-

Brian

[troma]

I'm wondering exactly how "near" to the spot elevation you are.  If you are exactly on the spot, the surface should be exaclty the same. Try zooming in.  There might be a steeper slope in some areas than others; in a flat area you will get close to the same elevation as the spot even if you're off it a bit, in a steep area it will be more noticeable.

[BrianD17]

Thanks for the reply and it's a fair question.  I put a spot on the eg surface and snapped it to the survey point and have attached.  It's not the same point i referenced in the original question but same issue.  I'd be happy with pretty close but a couple of inches is just too much.  The spots are the middle of the street so it should be somewhat flat.

[troma]

Do you have any edits recorded in the surface properties?

[mathewkol]

Look in surface properties, definition tab. Do you see any "transformed by" entries? This would mean that the surface was moved.

[BrianD17]

Yes, but I'm not sure what they mean.

[troma]

You've built this surface from contours, not from cogo points.

[mathewkol]

For the top half of your image it doesn't matter. There are none in the bottom half so you're good on this front.

[BrianD17]

correct, followed one of the tutorials.  I'm not sure what cogo's are.

[mathewkol]

But you're not using points, you're using contours to define your surface. Hence the difference in elevation.

[troma]

cogo points would be the spot heights from the survey that you are looking at (probably)

Where did you get the contours from?

[BrianD17]

the contours and the spots were broken out of a survey file.

[Neilw_05]

Just an FYI, in the Civil 3D world when we say a surface was built from survey, many of us take that to mean the survey module was used to create the components of the surface. It is not the same as using points, breaklines and contours from a CAD file to build a surface. So in future posts it would help to make that distinction as the solutions to a problem depends on what method was used.