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Most Accurate Output for Autocad Surface Generation

Hey All,

Looking for advice on the most accurate file type to bring into Autocad to generate a surface from. We’ve got the process of tying in ground control points with less than an inch of vertical deviation from the actual surveyed elevations, but when we create a surface from the .las, the elevations at the GCP’s are different than what they identify as in Pix4d. 

Hi Erik,

The best candidate here would be the densified point cloud. 

Is the shift only for GCP’s or all the point cloud is shifted? Do you use the same coordinate system for the GCP’s and the outputs in the mapper?

Did you followed the steps presented by Christina here: https://support.pix4d.com/hc/en-us/articles/202561559#gsc.tab=0 

Let me know,

Cheers,

 

 

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Thanks Ina, That is the procedure and output we are using, we’re going to try a few more variables and compare the results.

 

Erik,  we had a lot of trouble getting our large point clouds into civil3d.  An alternative, is to generate .2’ contours in step three in dxf, you can even use this to filter vegetation.  open in civil and then create a surface.  Run a points to surface and determine the bias from the move.  With a little excel work you can find the bias and shift the surface.  Make sure you are using independent check points outside of pix4d, as pix will use a checkpoint as an MTP and will not be representative of overall accuracy.

 

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