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Information
Transformation: | LowPass | ||
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Transformation Group: | Filter | ||
Description: | Low pass filter for discrete time series. This transformation calculates the following difference equation.
Here x is the input, y is the output, t denotes time, b0 to bM are the feedforward coefficients and a1 to aN are the feedback coefficients. When this transformation runs, then it first retrieves the required previous output values from previous runs, if available. |
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When using coefficient set functions (available since build 30246), the a and b coefficient elements can contain tags between "@" signs (e.g. "@NUMBER@") that refer to location attributes that are defined in the locationSets configuration file. The tags are replaced by actual values. These values can be different for different locations and time periods. See 22 Locations and attributes defined in CSV files, Shape-DBF files or external tables for more information.
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a
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- One or more feedback coefficients (a1 to aN).
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b
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- One or more feedforward coefficients (b0 to bM).
Output
Output variable y(t). For each calculation of y(t) the previous output values y(t-1) to y(t-N) are required. When this transformation runs, then it first retrieves the required previous output values from previous runs, if available. If one of these previous output values is missing, then that output value is ignored. Effectively this means that it behaves as if all previous missing output values would be 0.
Configuration Examples
| Code Block | ||||
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<variable>
<variableId>input</variableId>
<timeSeriesSet>
<moduleInstanceId>FilterLowPassTest</moduleInstanceId>
<valueType>scalar</valueType>
<parameterId>H.obs</parameterId>
<locationId>location1</locationId>
<timeSeriesType>external historical</timeSeriesType>
<timeStep unit="day"/>
<relativeViewPeriod unit="day" start="10" end="43"/>
<readWriteMode>editing visible to all future task runs</readWriteMode>
</timeSeriesSet>
</variable>
<variable>
<variableId>output</variableId>
<timeSeriesSet>
<moduleInstanceId>FilterLowPassTest</moduleInstanceId>
<valueType>scalar</valueType>
<parameterId>H.m</parameterId>
<locationId>location1</locationId>
<timeSeriesType>external historical</timeSeriesType>
<timeStep unit="day"/>
<relativeViewPeriod unit="day" start="10" end="43"/>
<readWriteMode>add originals</readWriteMode>
</timeSeriesSet>
</variable>
<transformation id="filter low pass">
<filter>
<lowPass>
<inputVariable>
<variableId>input</variableId>
</inputVariable>
<coefficientSet>
<a>0.4</a>
<a>0.3</a>
<b>0.2</b>
<b>0.1</b>
</coefficientSet>
<outputVariable>
<variableId>output</variableId>
</outputVariable>
</lowPass>
</filter>
</transformation>
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The example below uses coefficientSetFunctions (available since build 30246). Here the coefficients are defined in coefficientSetFunctions, where @a1@, @a2@, @b0@ and @b1@ refer to location number attributes that are defined in the locationSets configuration file.
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<variable>
<variableId>input</variableId>
<timeSeriesSet>
<moduleInstanceId>FilterLowPassWithCoefficientSetFunctionsTest</moduleInstanceId>
<valueType>scalar</valueType>
<parameterId>H.obs</parameterId>
<locationId>locationWithAttributes5</locationId>
<timeSeriesType>external historical</timeSeriesType>
<timeStep unit="day"/>
<relativeViewPeriod unit="day" start="10" end="43"/>
<readWriteMode>editing visible to all future task runs</readWriteMode>
</timeSeriesSet>
</variable>
<variable>
<variableId>output</variableId>
<timeSeriesSet>
<moduleInstanceId>FilterLowPassWithCoefficientSetFunctionsTest</moduleInstanceId>
<valueType>scalar</valueType>
<parameterId>H.m</parameterId>
<locationId>locationWithAttributes5</locationId>
<timeSeriesType>external historical</timeSeriesType>
<timeStep unit="day"/>
<relativeViewPeriod unit="day" start="10" end="43"/>
<readWriteMode>add originals</readWriteMode>
</timeSeriesSet>
</variable>
<transformation id="filter low pass with coefficient set functions test">
<filter>
<lowPass>
<inputVariable>
<variableId>input</variableId>
</inputVariable>
<coefficientSetFunctions>
<a>@a1@</a>
<a>@a2@</a>
<b>@b0@</b>
<b>@b1@</b>
</coefficientSetFunctions>
<outputVariable>
<variableId>output</variableId>
</outputVariable>
</lowPass>
</filter>
</transformation>
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