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Can you please tell me the accuracy for a Gerber to ODB++ translation?

Can you please tell me the accuracy for a Gerber to ODB++ translation?

This is what I have observed during our testing:
Step 1: Translate AutoCAD data to Gerber RS-274X data (using our own Gerber export program).
Step 2: Import the Gerber data into ACE 3000, then export as ODB++.
Step 3: Import the ODB++ data into ACE 3000, then export as DXF.
Step 4: Import the DXF data into the original AutoCAD file to overlay.


A lot of steps, but really the best we could do based on limited data import options in AutoCAD.
Comparing the original and new data, I found a .00005" worst case difference in geometry locations (basically accurate to 4 decimal places). This is not necessarily a show stopper, but it does raise questions. Your web site claims a 1/10 nanometer accuracy, so I wonder if it is something I am missing during the conversion set-up. I tried setting the 'Database Accuracy' to 1/10000 micron, but that did not make a difference.


To eliminate the Gerber data as a possible source of the discrepancy, I tried the following procedure:
Step 1: Translate AutoCAD data to Gerber RS-274X data.
Step 2: Import the Gerber data into ACE 3000, then export as DXF.
Step 3: Import the DXF data into the original AutoCAD file to overlay.


There was no measurable difference between the 2 data sets with the measurement precision set to 8 decimal places, which points to the ODB++ translation as the source of the error.
Also, I tried the first procedure above, but modified step 2 by performing the ODB++ translation with another translator. The end results showed accuracy to 8 decimal places as well.
Please let me know if this sounds right or if there is anything I can do to improve the results.

Thanks for your excellent questions.  


The accuracy limitation occurs during your Gerber export.  Gerber format is primarily for PCB design, so by default ACE outputs Gerber files to Inch units with 4 decimal places; which is typically good for most PCB designs.
ACE allows you to increase the accuracy by adjusting the "Decimal Digits" up to 6 places, see screen capture:
http://screencast.com/t/D2RmMjux15h

Note:  For extreme accuracy in the Gerber format you can export with units of "Millimeter" and use "Decimal digits" of 6.  This means gerber files will be exported with an accuracy of 0.000001 millimeters  (1 nanometer). 

Here's some other links on the ACE User forum which explain the "Decimal Digits" in more detail:
http://forums.numericalinnovations.com/post/what-would-be-the-difference-in-the-following-gerber-digits-integer-decimal-3-4-and-5277050
http://forums.numericalinnovations.com/post/the-boundaries-of-my-autocad-drawing-did-not-line-up-perfectly-with-the-gerber-and-5972323


Thanks again for your questions, and please let me know if I can assist you any further.
Please note, the above links have been updated. Please use the links below.

What would be the difference in the following: Gerber digits (integer.decimal) 3.4 and 3.5 and 4.6 ?
https://support.numericalinnovations.com/support/discussions/topics/14000002813

The boundaries of my AutoCAD drawing did not line up perfectly with the gerber and curves that I drew came out as jagged lines in gerber.
https://support.numericalinnovations.com/support/discussions/topics/14000003001

 

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