Have you happened the same?

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DelioPontes
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Have you happened the same?

Post by DelioPontes »

Hello everyone!

Last week I was doing a demo for a client that we already work with him + - 20 years but in classical topography (eg equipments alignment).

In certain areas of the factory, they don´t have any "as built" so they need survey of that areas.
But first they want to know how far it is possible to use the laser scanning technology.

The engineer that follow in our demonstration already knew the process by other laser scanning company that already did there other demos.

The first question he did me was, what is the accuracy of the points cloud? I told him that we can expect +- 6mm but all depends of the material scanning.
When I finished the scan, for my suprise! he and other colleague picked a tape metric and measure some corners to compare with the points cloud, he was happy with the results and told me the other laser scanning company guaranteed that they can offer +- 2mm accuracy which did not come to be confirmed at the end...

Have you happened the same? is that it seems that anything goes in this area until cheat the clients...
Last edited by DelioPontes on Tue Jul 24, 2012 3:03 pm, edited 2 times in total.
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Matt Young
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Re: Have you happened the same?

Post by Matt Young »

It is impossible to state accuracy to the un-educated.

Those who lie about it are making problems for the rest of us.
If you don't see that there is nothing, then you are kidding yourself.
Oatfedgoat
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Re: Have you happened the same?

Post by Oatfedgoat »

I would never put my name to a +/- 2mm accuracy. It simply isn't achievable with the needed level of confidence from terrestrial scanners in my opinion.
+/- 6mm is pushing it. Depending on instruments used etc it is unlikely the control, registration, CAD interpretation could be confidently with in +/- 6mm across the an entire area modelled.
Meshes are probably just about doable though.
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DelioPontes
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Re: Have you happened the same?

Post by DelioPontes »

These companies buy a scanner, the sofware and they think are ready to start working in any kind of job!
Also most of the times, they don´t have any surveyor (with experience) in the company

And forget most of the times, new projects are based of the 3d model they delivered

Besides the laser scanning I think we should give a extra work done manual, with a total station and digital level on the most important on the equipments (centel lines, levels of the structure etc) and force the 3d model move to that positions (also shoud be deliver a report with this kind of information)

I already followed some new projects based on point clouds, and when it comes to connecting with the old equipments always got errors.

And the client paid a previous job to facilitate the new projects for nothing! and now have to pay to revise the new project...
Last edited by DelioPontes on Tue Jul 24, 2012 3:06 pm, edited 1 time in total.
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Re: Have you happened the same?

Post by tbwester »

Well point cloud accuracy is still an ambiguous term. Like you said, it depends... And not just on the instruments specs.

I think the best thing to do is to give a number based on your working experience, and examples of past projects.

Anyone can give a number, but not many can give an explanation of errors associated with a past project.
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