A call to GridCoverage.forConvertedValues(true) is supposed to create a GridCoverage where all sample values have been converted to "geophysics" values (i.e. values in the units of measurement given by SampleDimension.getUnits()). If the values before conversion had some sentinel values used for missing data (e.g. "999 = no data"), then those values shall be converted to NaN values. However in Apache SIS 1.0, the forConvertedValues(true) method sometime fails to recognize that it needs to change the image data type from an integer type to a floating point type in order to be able to store NaN values.