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TSTool Documentation <br />Introduction - 8 <br />3. The period of a time series is defined by star t and end date/time values, using appropriate precision. <br />4. An analysis period may be used to indicate wh en data processing should occur. <br />5. Output is typically formatted for cale ndar year (January to December) or water year (October to <br />November). Additionally, a year type of NovToOct has been implemented to represent November to <br />October and additional similar year types may be implemented in the future. C alendar year is the <br />default but can be changed in some commands. <br /> <br />A date/time has a precision. For example , 2002 -02 has a monthly precision and 2002 -02 -01 has a <br />daily precision. Each date/time object knows its precision and “extra” date/time information is set to <br />reasonable defaults but generally are not used (e.g., hour, minute, and second for a monthly prec ision <br />date/time are set to zero and the day is set to 1). The date/time precision is important because TSTool <br />uses the date/time objects to iterate through data, to compare dates, and to calculate a plotting position for <br />graphs. Specifying date/time info rmation with incorrect precision may cause inconsistent behavior. <br /> <br />The TSTool documentation and user interface typically use ISO 8601 International Standard formats for <br />date/time information. For example, dates are represented using YYYY -MM -DD and times a re represented <br />using hh:mm:ss . A combined date/time is represented as YYYY -MM -DD hh:mm:ss . In order to <br />support common use, TSTool also attempts to handle date/time formats commonly used in the United <br />States and other locales . In such cases, the length o f the date/time string and the position of special <br />characters are used to make a reasonable estimate of the format. Using ambiguous formats (e.g., two - <br />digit years that may be confused with months) may cause errors in processing. Adhering to the ISO 8601, <br />standard formats will result i n the fewest number of errors. The input type and datastore appendices <br />discuss date/time issues with various data formats. <br /> <br />Plotting positions are computed by converting dates to floating point values, where the whole number is <br />the year, and the fraction is the fractional part of the year, considering the precision. The floating -point <br />date is then interpolated to screen pixels or page coordinates . In most cases, the high -precision date/time <br />parts are irrelevant because they default to zero. However, in some cases the precision can impact plots <br />significantly. For example, when plotting daily and monthly data on the same graph, the monthly data <br />will be plotted ignoring the day whereas the daily values correspond days 1 to 31 . The ability to plot <br />monthly data mid -month or end -of -month has not been implemented. The TSView Time Series Viewing <br />Tools Appendix provides examples of plots. <br /> <br />The date/time precision is very important when performing an analysis or converting between time series <br />file formats. For example, a file may contain 6Hour data using a maximum hour of 24 (e.g., 6, 12, 18, <br />24). When reading this data, TSTool will convert the hour 24 values to hour 0 of the next day. <br />Consequently, the hour and day of the origin al data will seemingly be shifted, even though the data are <br />actually consistent. This shift may also be perceived when converting from hourly data to daily data <br />because the hour can have a value of 0 to 23, whereas days in the month start with 1. The per ceived shift <br />is purely an artifact of time values having a minimum value of zero. Some commands will allow an <br />automatic conversion of 24Hour interval data to Day interval data to avoid hour offset issues. <br /> <br />TSTool understands leap years and days per month. Consequently data formats that do not properly <br />implement leap years or simplify time by assuming a constant number of days per month may result in <br />missing values in data when read into TSTool. <br /> <br />TSTool does have the capability to handle time zone in small interval (hour, minute) data. However, fully <br />represent ing time zone and daylight savings offsets is somewh at complex and TSTool for the most part <br />does not perform time zone conversions or normalization. <br /> <br />20