Add additional validation checks
- Check thickness
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max_thickness > mean_thickness
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- Check dates
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max_date > date -
to_date > from_date -
from_date, to_date ~ date, max_date
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- Check from_elevation < to_elevation
- Check flag remarks
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survey/glacier not null if glacier.flag == 'other' -
survey/glacier/band not null if band.flag == 'other' -
survey/glacier not null if point.flag == 'other'
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