Hello everyone:
I have a few Point features in an ESRI shapefile with the value for the attribute FROMAGE as 999.000 (unit Ma). When I loaded these point features to GPlates, the value of FROMAGE for these point features became distant past. I included the few snapshots to demonstrate this unexpected behavior. The snapshots showed how in the XML file the attribute for tag was UpperAge. The value assigned to UpperAge was 999.000, but GPlates then interpreted the value to be DistantPast.
Thank you very much for taking time and efforts to look into this issue.
Hi Lavie,
Hmm yes, this is actually a holdover from the old PLATES4 line format days where 999.0 (and -999.0) were treated as special values that represented the infinitely distant past (and future). The Shapefile code in GPlates also does this conversion (ie, it sees 999.0 and changes it to DistantPast, which represents +infinity).
This is unfortunate now that we have 1Ga reconstruction models (where 999Ma represents an actual reconstruction time, not the infinitely distant past).
As a workaround you could change the value 999.0 in the Shapefile to 1000.0 (or something outside the non-inclusive range [998.9, 1000.0]).
I’ll look into changing the 999.0 value in GPlates, perhaps to a much larger value. For older models (eg, 0-250Ma or 0-410Ma), 999Ma would then remain as 999 (ie, no longer get converted to DistantPast), but that’s probably fine because presumably no one would reconstruct an old model back to 999Ma anyway (if they did then the features would just disappear).
Hello John:
Thank you very much for your response regarding the issue ‘Unexpected values of FROMAGE’. May I please whether this issue has been address in the latest version of pyGPlates and GPlates? For your reference, I have been exploring the plate tectonic model associated with the publication “Earth’s tectonic and plate boundary evolution over 1.8 billion years” by Cao et al. (2024) (here is the zenodo link to the supplementary data including the model: Earth's tectonic and plate boundary evolution over 1.8 billion years (supplementary data)). I found the several polygon features had 999.00 Ma as the value for FROMAGE, and when I loaded them to GPlates and pyGPlates, these polygon features had Distant Past as the value for FROMAGE.
Unfortunately not yet, but I’ve added an issue for the next release (as this needs fixing now that we have 1Ga+ models where 999 represents an actual valid time).
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Thank you very much for your response.
