Original Ground Data

User Q & A (Post Here)
1

When obtaining Original Ground Data from engineers normally this information is provided by contours in a CADD file and sometimes but not often we get surfaces. We never get points. In a perfect world what form is the most accurate for creating the best Original Ground Surface?

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Best data to worst data

The original data ie the points and breaklines or drone flight point cloud that was used to form the model in the first place.

Failing that the TIN model in a landxml format that uses the point and line data - if not a landxml then a CAD file of 3D Faces can also work.

Failing that the contours in a CAD file

Failing that contours in a PDF file

Failing that for a road job the cross sections that show existing ground and or the profiles that show existing ground at centerline and or at the ROW lines.

Failing that guess or fly the site or survey the site yourself is the only option

Hope this helps

Alan

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20036 - BASE.dwg (570.7 KB) 20036 - POINTS.dwg (1.3 MB)

Alan,

The BASE file was what we received initially. We requested and received the Points file. Would you make a surface with these points or make your own contours and then make a surface? The land is very flat so the contours they provided show large areas that are not reflective of the point data.

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I would make my own surface from the point data - for the exact reason you say in your email - if you use the contours you are going to get large flat areas that don’t match the measured data - so just use the measured data and toss the contours - you may want to contour your model and check the contours against their model - as they may have had some breaklines in their data / surface that controls the way the surface is formed - also check their edge vs your edge to make sure that is as you want it. If their contours follow some hard lines in the TIN then you likely need to build those breaklines in your model also to get the contours to match - draw those in with Quick line or Takeoff lines command

Alan

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Alan,

The points came in as blocks so I used the “Create from CAD” command to create the points. I found the points created all show an elevation of 2.1-2.2’ lower than the text values that show on the blocks. In the properties for the blocks the elevation shows the lower value that corresponds with my created points and not the text in plan view for the blocks. This higher elevation in the text for the blocks corresponds with the contour values that were given. What could cause this?

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I cannot answer why the Blocks are lower than the text labels say they should be - one of the joys of AutoCAD I guess

The blocks are nested 3 levels deep (I had to explode them 3x to get them to be lines and text - the lines of the X are at the lower elevation). Even the text is placed at the lower elevation as well so it says one value but is placed at the lower elevation.

I did the following

  1. Exploded multiple times to get down to text and lines
  2. Used Change Elevation to set all text and lines to undefined elevation
  3. Used the elevate lines command using Text Insertion and the line intersections only option with a tolerance of 7’ to elevate the lines from the text
  4. Used Create from CAD to create points at the intersections of all the lines (these are 2D only
  5. Used the lines to make a surface - used advanced select to select the lines only - (surface is correct at center of X
  6. Used Change elevation to elevate the points to the surface - because they are at the center of X they are correct on the surface also
  7. Used the points to create surface
  8. There is a berm along N side of project - I added a Breakline through the high points - I assume that is correct but without plans hard to tell without seeing the site

Hope this helps - long winded I know but still it works

AlanSpot Level Points.vce (950.0 KB)

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Not long winded. I would say thorough. It was what I needed to understand what would be needed to process this set of data. All of this is based on the issues we have been having relating to my original question. We have almost exclusively used the engineers CADD contours. Up until recently this has provided decent results. For the last few months it appears when we get a job and go out and check existing ground we are getting sufficient misses based on those contours. We are trying to lessen these issues on the front end by trying to receive better data. This helps me understand the work that may or may not be needed to produce a better original ground surface based upon what format different engineers may provide. As always thank you for your help in providing not only a step by step method but the thought process behind it.

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