Under which conditions is the 'numerical' value empty?

[Mac2]

My application extracts data from files via the -X XML format. I import both the et:val ( numerical tag value) and the et:prt values into a database.

I just noticed that sometimes, e.g. for ShutterSpeed, the numerical value only contains data for some of the files. For example, shutter speeds reported as 0, 0.5, 0.6 and 2 in et:prt have no corresponding numerical value. But et:val is filled for values like 1/1000 (0.001) or 1/90 (0.0111111111111111).

What is the logic behind this?

[Phil Harvey]

The "et:val" is output only if it is different from the print-converted "et:prt" value.  I wish I had named these "num" and "val" as with the -j and -php options, but that's water under the bridge.  This is mentioned in the -j documentation, but not for -X.  To cover -X, -j and -php, I will mention this in the -l documentation:

    -l (-long)
         Use long 2-line Canon-style output format. Adds a description and
         unconverted value (if it is different from the converted value) to
         the XML, JSON or PHP output when -X, -j or -php is used.

- Phil

[Mac2]

Understood, thanks.