Generating Existing tunnel from point clouds...anyone?

Hi,

we are trying to generate a surface model of some tunnel walls from Point Cloud Data.  I have tried a few methods including Bentley Descartes as described in this youtube video...

Also we have tried exporting the point cloud information to ASCI and importing back in with the intention of generating a mesh.

The Bentley Descartes option seems like it will be too long winded to get the accuracy we need and the ASCI solution is too memory intensive to work and Microstation tends to crash.

Perhaps there is no need to generate a surface model of the tunnel wall...

Im not sure this is the right forum but if anyone can point me in the right direction I'd be very greatful!

Thanks

Abe

  • Hi Abe,

    a couple of comments:

    Unknown said:
    Also we have tried exporting the point cloud information to ASCI and importing back in with the intention of generating a mesh.

    My experience is this is a wrong way to go often, because there are too many points, so the result is huge mesh and not alway precise.

    Unknown said:
    The Bentley Descartes option seems like it will be too long winded to get the accuracy we need and the ASCI solution is too memory intensive to work and Microstation tends to crash.

    I think you should start with defining your requirements in terms of input data parameters (density, expected accuracy defined by scanner used and site conditions...) and required accuracy of the model.

    Unknown said:
    Perhaps there is no need to generate a surface model of the tunnel wall...

    This doubt is perfectly valid, but it's not possible to investigate it, because it's not clear for what purpose you need to create the models.

    In my opinion there is no common solution that fits all. Recently we evaluated similar request with my customer and at the end they decided to vectorized point clouds manually (after participating on special 3D training). In this specific case a demand for accuracy was not so high and at the same time they appreciated ability to explore data based on operators knowledge of the real situation and to choose a proper tools. But if you have Descartes license already, it's good to think about to use it.

    You should also to check specialized software like 3dResharper (I am sure more similar application exist), because despite of they are not general like MicroStation and/or Descartes, for the specific case they provide better tools and alghoritms. And it's easy to load the results into MicroStation for further processing.

    With regards,

      Jan

  • Hi Abe
    What you do, is determined by what your client wants from you.
    If all he wants is a video (for visualizing) moving thru or to Measure between points in the Tunnel Point Cloud, you don't have to generate Vector Graphics.
    I doubt you want to use ALL the points generated in the Point Cloud unless you need an EXTREMELY HIGH level of accuracy. There can be Billions of Points in a Point Cloud. You can lock onto the points in a Cross Section of the Point Cloud to draw a Vector Cross Section of the Tunnel. You can then Project the Graphical Cross Section from Point A (at the beginning of the Tunnel) to Point B (at the end of the Tunnel) but this would not be HIGH DETAIL (all the bumps in the concrete walls). You can also generate several Cross Sections along the Tunnels Point Cloud and Project Surfaces between the Cross Sections or along a path(s) you generate locking onto points along the Tunnel Point Cloud. If you need the HIGH LEVEL of DETAIL you could break the Point Clouds down to small sections and generate Meshes but that is just triangles between each of the points. You could also trim the Point Cloud down to 50% of the points and generate the XYZ from ?% of points you want but you are loosing Detail. When you have the Vector Graphics you can view the Point Cloud with the Vector Model to see where the Points Fall (In front or in back of the Vector Graphics) and adjust your Vector Model if necessary.
    Just what does your client expect from you?

    I Hope This Helps Someone Reading This!  (Intergraph>PseudoStation>MicroStation user since 1980's)

  • Jan/George,

    thanks to you both for your reply's.  The main thing I took from it was "What do we need the model for".  I think the answer to that is very simple but need a little explanation first...

    We need to be able to identify the following to enable us to complete the scope of works on this job...

    - Ventilation shafts

    - Cross passages

    - Tablets (labels on the tunnel walls at 50ft intervals)

    - Construction joints

    - Cracks in the lining

    But as well as that, we need a 3D model to enable other disciplines to do their work for example hanging tunnel lighting, structures inside etc.

    My thinking now is that we can get all the details for the bullets above direct from the point cloud.  And we can also generate the tunnel

    surface models using the technique above in the video.

    However, I now have the problem of being able to manipulate the points cloud so we identify the items above.  The points cloud looks pretty ambiguous at full density...at low density its not much better really.  The image below is at full density...you can see the brick work on the left hand side close to the camera but too dens from then on and there's no definition to the tunnel surface.

    I appreciate this may be the wrong place to ask help for this..which is the best forum to ask questions related to point clouds?

     .

  • Hi Abe1984,

    Yes, the Model By Section tool is probably the best tool to model the tunnel.

    As for visualization I would suggest that you try different  Point Cloud Presentation style (i.e. : intensity + elevation might give the best result).

    HTH,

    Mathieu



  • Abe1984
    I don't know if your Point Cloud Data is enough to pick out cracks in the surfaces (depends on size). You may not be able to pick-out the Construction Joints either (same reason). The Tablets (If just spray painted on the Surface) won't show but smooth metal signs may be possible to see smooth areas. Cross Passages you should be able to see and Ventilation Shafts may be able to seen depending on the cover. It would have helped if the Point Cloud had RGB (Color) values. As far as generating Sections and projecting between the sections for the 3D Model you have plenty to create the sections and do projections.

    I Hope This Helps Someone Reading This!  (Intergraph>PseudoStation>MicroStation user since 1980's)