Land Surveyor Community Forum

Hi,

any way to fix a topographic surveyed map upon a 3D scan survey?

I have surveyed a site and the site surveyed by 3D scan as well, so there are deference in the location of objects in the site between them, but not equal in deference part of the site, the site is to be used for reconstruction proposes and it's needed to be fixed both maps,

any suggestion or any way here?

 

Regards 

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Replies

  • The best way to find out mistake is to make traverse and scan survey by the same targets as a4 crosses.

    I had the same problem year ago when we made a survey of all concrete in site and our head decided to make a 3 d model of full site.

    So the biggest error in 3D traverse was 4 cm. and we decided to recheck all.

    The mistake was in scan processing the APP had wrong decission and scale at all.

    So try to do same as we did,Good luck!

  • You can do some control scans using your control grid. But then you'll have to redo the scan registration including the control scans. Since the scanning task didn't include the control network they are most likely displaced. 

    I believe the scan crew used targets to link them as they went. Though it´s a good practice it's not flawless and I experienced in some projects.

  • You technically do it the opposite way of what you are doing. 3D scans are fixed to conventional survey coordinates. If your scans and total station objects aren't the same distance apart, then one of them is wrong. Either your traverse/control has error or your scan registration has error. Did the 3D scan include common targets? That's step one.

    • If the scan team is using targets, then you need to also locate those targets. After that, you identify those targets in the 3D scans and use the coordinates you obtained with your conventional surveying and rotate the scans. I'm versed in Leica Cyclone and Autodesk if you need help with that.

      This is a gross over simplification of everything that goes into it, but that's what's going on.

      Coupling 3D scanning with conventional really starts before the scans are done. If you don't have common targets, you'll have to identify specific things that you can shoot and pick out of the scans of you have them. I choose signs, corners of forms, and sometimes paint marks. That method is very low accuracy however, and I only do it when my crews have screwed up and we are only looking for dirt quantities.
      • Yeah, I agree, marrying laser scanning with conventional equipment needs to be carefully planned, and common targets are a must. 

    •  Thanks William Kenter

      the 3D scan done by other team are using continuously targets by scanning more areas use new targets, 

      • Hi Mohammad, Further to William's comment I think your first task is to decide whether you need to use a plane grid with no scale factor but this would depend on the size of the site. If more than say 100 acres or so curvature of the earth may then come into 'play'.... and force scale factors. If your scan is GPS based for the 'control' then it will be related initially to the 'Earth' and therefore a scale factor will be required to bring back to your plane grid. As total station control, completed correctly and with care should provide more accurate information then your scan data should be scaled and orientated to this control. If the scanning was done independently and no common control was fixed with your total station AND the scanner then the choice is to transform or re-scan....  cheers, hope this is a bit helpful, David

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