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LSST Data Management Base Package
LutMap Attributes

LutMap Attributes

LutEpsilon

The relative error of the values held in the took-up table.

LutEpsilon is used when simplifying a LutMap, to determine if the LutMap should be considered linear. Setting a larger value makes it more likely that a LutMap will be replaced by a WinMap (i.e. a linear Mapping) when simplified.

The default value is the value of the system constant DBL_EPSILON (typically around 1e-16 or 2E-16). If the values in the look-up table were derived from single precision data, it may be appropriate to set this attribute to a value around 1E-7.

LutInterp

This attribute indicates the method to be used when finding the output value of a LutMap for an input value part way between two table entries. If it is set to 0 (the default) then linear interpolation is used. Otherwise, nearest neighbour interpolation is used.

Using nearest neighbour interpolation causes nan to be returned for any point which falls outside the bounds of the table. Linear interpolation results in an extrapolated value being returned based on the two end entries in the table.