Download ODV4 - User's Guide - Ocean Data View

Version 4.7.3
length as well as the quality flag schema used for the variable’s quality flags. Note that
the first twelve meta-variables are mandatory and that they may not be deleted or reordered.
Some modifications, such as changes of the collection’s data field, data type, or the labels, units, and number of decimal places of variables, are simple changes that can be
dealt with by recording the new entries in the collection’s settings or variables files.
Adding or deleting variables, changing the collection’s primary variable or altering the
data type or quality flag schema of a variable are critical changes that require a complete re-writing of the metadata and data files of a collection.
Please note that if collection re-writing occurs, the new collection will always use the
new ODVCF6 collection format (.odv collection), even if the original collection was
ODVCF5 or ODVGENERIC. The new ODVCF6 collection format requires ODV 4.6.0 or
higher.
12.5 Key Variable Associations
Many derived variables require identification of the input variable(s) needed for the
calculation of the derived variable. This identification of key variables is done during
the first definition of the derived variable, and the selected variables are remembered in
the collection’s settings file. If the derived variable is requested again at a later time, the
stored key variable information is used, and the user is not prompted again.
You can inspect and modify the current key variable associations using Collection >
Identify Key Variables. The Identify Key Variables dialog will appear, showing lists of key
variables on the left and data variables on the right. Associated items are marked with
an asterisk (*). You can click on such items in any of the lists and ODV will show the associated item in the other list. You may break the association by pressing Undo; pressing Undo All will break all association and leave all key variables undefined. You establish an association by selecting the relevant items in the two lists and pressing Associate. Items in the key variable list that are not included in the list of data variables may
be marked as not available by pressing the Not Available button. Such items are marked
in the key variable list by a minus sign (-).
Important Note: Errors in the key variable associations can lead to wrong and meaningless values of affected derived variables. For instance, imagine the key variable Practical
Salinity [psu] was erroneously associated to data variable Oxygen [µmol kg-1]. This
would cause all derived variables requiring Practical Salinity [psu] as input variable
(e.g., potential temperature, potential density, etc.) to use oxygen values instead of salinities and return wrong values. Verifying the validity of key variable associations using option Collection > Identify Key Variables should be the first check, whenever you receive doubtful derived variable values.
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