Importing Controls

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3DS Tech
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Importing Controls

Post by 3DS Tech » Wed May 01, 2019 1:47 am

I am trying to import controls to my latest scan and the controls I received from the client are in UTM. When I import the controls, they are out by up to 85mm. Is there a conversion factor or formula I need to use? I tried multiplying to ground points by multiplying by the UTM conversion factor of 0.99959915 but that made a bigger mess.
Anyone have any experience with this ?


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Re: Importing Controls

Post by jamesworrell » Wed May 01, 2019 3:21 am

You want to go bigger to get back to ground distances where you are? Try dividing by the scale factor - document your scaling point/origin! (hint - not 0,0)

Two options though - you can lock your bundle and move it - or use the control to tweak your registration. The second option assumes you are using say cloud to cloud with a non-survey grade scanner. If you are using survey grade scanners and targetting - you might find your work is better ;-p

To validate the data "separately" - as in whole-bundle shift:
- freeze your scan data;
- create a new rego;
- in new rego, add the control scanworld as home, add your data, auto-find by target id (assuming you have called your targets the same as control values - have you set target heights? What scanner - as in P or C series that are levelled or something else?);
- register - check values - should be within expected tolerances.

Now you can decide whether you want to "rubber sheet" your scanning to better fit the control or just plonk the bundle onto control.

If you are using C/P series with targets, you might consider just moving the whole thing using coordinate system - set by points - pick a vertex with known value and supply bearing to second point - then check the derived values of other control points versus control file for quality assurance.

If using 2-points - you will likely want a point near the middle of the site to try to mitigate the scale factor. Also depends on how big a site we are talking - but 85mm gives a clue - say 400 - 500m? You'll definitely notice scale factor.

Now for the fun part - they putting this in Revit? If so and using geodetic coordinates, tell them they are mad (must be a big building/campus?).
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Any derivatives - eg CAD can be scaled back to geodetic - just document your scale factor to apply and scale point (origin).

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