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Subsections

7.1.2 Reserved Keywords

 

7.1.2.1 PTYPEn Keywords

  The  value field shall contain a character string giving  the name of parameter  n. If the PTYPEn keywords for more than one value of n have the same associated name in the value field, then the data value for the parameter of that name is to be obtained by adding the derived data values of the corresponding parameters. This rule provides a mechanism by which a random parameter may have more precision than the accompanying data array elements; for example, by summing two 16-bit values with the first scaled relative to the other such that the sum forms a number of up to 32-bit precision.

7.1.2.2 PSCALn Keywords

  This keyword shall be used, along  with the PZEROn keyword, when the nth FITS group parameter value  is not the true physical value , to transform the group parameter value to the true physical values it represents, using Eq. 7.2. The value field shall contain a floating point number representing the coefficient of the linear term in Eq. 7.2, the scaling factor between true values and group parameter values at zero offset. The default value for this keyword is 1.0.

7.1.2.3 PZEROn Keywords

  This keyword shall be used, along  with the PSCALn keyword, when the nth FITS group parameter value  is not the true physical value, to transform the group parameter value to the physical value. The value field shall contain a floating point number, representing the true value corresponding to a group parameter value of zero. The default value for this keyword is 0.0. The transformation equation is as  follows:


physical_values = PZEROn + PSCALn × group_parameter_value(7.2)


next up previous contents index
Next: 7.2 Data Sequence Up: 7.1 Keywords Previous: 7.1.1 Mandatory Keywords

5/13/1999