Introduction

The Plot Interface Definition File (PIDF) is the UDF interface file between a UDF definition and any application which uses data from that definition. This document is a full description of the PIDF and its fields. It is written with for both the general user and for anyone who might need to develop a PIDF for a specific UDF definition. It assumes at least a rudimentary understanding of the UDF concept and some of the terminology which is used in describing it.

The primary purpose of the PIDF is to allow an application program to identify what measurements exist under a UDF definition, to identify where those measurements are stored within the UDF data or header record, and to identify what units those measurements may be returned with including any necessary algorithms needed to produce those units. In addition the PIDF contains a large amount of default information: ranges, scaling, labels, and storage methods. What if any of this information an application chooses to use depends on the application.

The PIDF is a keyed ASCII file, that is each information field in the file consists of KEY WORD followed an entry. Data is blocked through the use of nested C-like structure statements enclosing a set of information field definitions. These structures take the form:

   struct YYYYNN
      {
      };

A PIDF contains 12 different blocks of information. In general, however not all blocks will apply to the measurements within a UDF and those not relevant are omitted. The possible blocks are listed below in the order in which they will be taken up with in this document.

1. General information.
2. Information on the defined measurement groups
3. Information on any defined binning in the UDF scan dimension.
4. Information on all imaging parameters.
5. Information on all physical units defined for the UDF measurements.
6. A description of accessible measurements under the heading sensor.
7. A description of accessible measurements under the heading array (scan) index.
8. A description of accessible measurements under the heading ancillary (calibration) data sets.
9. A description of accessible measurements under the heading mode (status).
10. A description of accessible measurements under the heading data quality.
11. A description of accessible measurements under the heading spin angle.
12. A description of accessible measurements under the heading pitch angle.

FILE NAME

The PIDF filename is the UDF Virtual Instrument acronym appended with .pidf.v2. The files are located in the directory indicated in the UDF database configuration file DB.cfg.

COMMENTS

Comments are allowed within the PIDF file and are defined as any text following a $. There is no comment termination symbol. The $ may occur anywhere on a PIDF line. The comment terminates the line. To continue a comment on a succeeding line requires another $. Any number of spaces may occur between a line entry and the beginning of a comment.

PIDF INFORMATION LINE

An entry line within the PIDF has the format:

The valid KEYWORDs will be described individually in the PIDF contents section.

Information lines in the PIDF are limited to 149 characters including spaces.

PIDF DELIMITERS

All entries in a PIDF file occur between the lines

   pidf v2_XXXX {
   };

NOTES

There is some terminology within the PIDF which has changed over time. In most cases the original terminology was based on a specific class of instruments or data usage. As more classes of instruments had their data converted into UDF/IDFS format and the usage of certain classifications of data generalized, the older terminology gradually shifted to a terminology which was more in-line with the actual usage. In contrast, however, the PIDF field names held to their original forms often leading to confusion. There are three shifts in terminology which probably account for 99% of any confusion in correlating the verbal descriptions of the PIDF contents with the actual field names. These are described below.

ARRAY INDEX - SCAN INDEX

The initial terminology for measurements which returned arrays of data was scan measurements and the indices that where returned with them were scan indices. This arose from the fact that the first array measurements were generally from instruments which scanned through a range of parameters. Gradually this terminology shifted to the more generic terminology of array data. While you will still see Scan used in the PIDF field designations, any descriptions will speak of arrays of data and array indices.

ANCILLARY DATA - CALIBRATION DATA

The VIDF and therefore the PIDF contain a data class which is known as calibration data. In the beginning this was data which was needed to calibrate the VIDF sensor class data and could be manipulated with the sensor data through a UDF algorithm. It was included in the UDF data record in such as way that it could be associated and returned with the sensor data. Gradually this class of data widened to include any data which needed to be combined with the sensor data but did not really calibrate it in any way. For example if Bx were defined as a sensor class measurement and By and Bz as associated calibration data then the measurements could be combined with a UDF algorithm to return B, B&phi and B&theta. The terminology shifted from calibration to ancillary.

STATUS DATA - MODE DATA

The UDF header records contain the mode data class. Initially this was information which gave the current instrument mode. Since this was assumed to remain static for extended periods of time it was put into the header record which contains slowly varying data. Over time this data class came to include other slowly varying data. At about the same time the terminology began to shift from mode data to status data.