Filling Out the Uniformly Sampled Class

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The <Uniformly_Sampled> class can be used in any table-type class (like <Table_Character>) when the table contains records which are uniformly spaced in some dimension (time, wavelength, distance, etc.). This class is used to define that dimension and interval rather than including an additional field in each row to hold the value explicitly.

There are certain types of data where this class can prevent a very large data file from increasing in size by %50. Such tables are predominantly used by software, not human readers scanning them by eye. For SBN data, our users generally prefer to see the additional column. So unless those two conditions apply to your data, you should include the extra column.

For additional explanation, see the PDS4 Standards Reference, or contact your PDS node consultant.

Following are the attributes and subclasses you'll find in <Uniformly_Samples>, in label order.

Note that in the PDS4 master schema, all classes have capitalized names; attributes never do.

<sampling_parameter_name>

REQUIRED

The name of the dimension of sampling (wavelength, time, etc.)

<sampling_parameter_interval>

REQUIRED

Distance between records in units of the sampling parameter. So if you're sampling in time, the interval might be 100 milliseconds, for example.

<sampling_parameter_unit>

REQUIRED

The unit associated with the sampling_parameter_interval.

<first_sampling_parameter_value>

REQUIRED

The value of the sampling parameter at the point where the data of the first record were recorded.

The data dictionary does not indicate whether this is the value at the beginning of the sample, in the middle, or at some other point. There is no descriptive field in this class, so if you're specifying Uniformly_Sampled information for your data your should use the <description> field in the table to provide this detail.
Note: The data dictionary is specifically ambiguous about the relationship between first_sampling_parameter and the first record in the table. It does specifically state that first_sampling_parameter must be less than last_sampling_parameter, but provides no way to associate either of those to the first (or last) record in the table. So, in general, you should also use the table <description> to indicate that correspondence, especially in the case where the last_sampling_parameter is actually associated with the first record in the table.


<last_sampling_parameter_value>

REQUIRED

The value of the sampling parameter at the point where the data of the last record were recorded. Also see the yellow box warning under first_sampling_parameter, above.


<sampling_parameter_scale>

OPTIONAL

This is actually the type of the scale. It must be one of the standard values Exponential, Linear, or Logarithmic. In the anscence of a <sampling_parameter_scale>, you can safely assume the scale is linear. If you use this value for one table in your product, though, you should use it for all of them.