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How to replace ATAN2 function from Excel's calculation?

Question asked by visualcraft on Feb 20, 2017

Hallo,

I'm migrating from an flat "database" in Excel, to a hopefully much faster and flexibel FileMaker relational database.

I'm using FileMaker Pro (not Advanced).

 

I have a few thousands of records with color values. The exact color of each record is expressed as a 3-dimensional tuple of numerical values; this is 3 fields with decimal values, containing the CIELab components of each record.

 

Lab_L

Lab_a

Lab_b

 

In the CIELab model, the color differences which you perceive correspond to distances when measured colorimetrically.

The a axis extends from green (-a) to red (+a) and the b axis from blue (-b) to yellow (+b).

The brightness (L) increases from the bottom to the top of the three-dimensional model.

CIELAB - Color Models - Technical Guides

 

I now need to calculate, from these three values, the Saturation and Hue of each of them.

 

I calculate Saturation as the distance from the 3-dimensional point to the central vertical axis:

(Lab_a ^ 2 + Lab_b ^ 2) ^ 0.5

This is no problem in FileMaker.

 

BUT.

In Excel, I used to calculate the Hue as the angle (0 to 360°) around this axis,

using the ATAN2-function, that apparently isn't available for FileMaker — I only find ATAN

In Excel >      Hue = ATAN2 ( Lab_a , Lab_b ) * 180 / PI()

 

I'm sure that there's a way to replace this one function by a more extended calculation. atan2 - Wikipedia

But apparently I just don't get it done without some help …

 

I would appreciate any help

 

Thank you in advance!

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