XTCE12 — SplineCalibrator order attribute too restrictive

As previously discussed, the @order attribute of the <SplineCalibrator> relates to the fit funtion that is used for interpolation and extrapolation.

Interpolation is implied when the @order attribute is used. Extrapolation has an explicit attribute.

Setting the order to zero effectively creates a "step" function, as the fit function is limited to zeroth order behavior. First order behavior creates a linear function, otherwise called a "point to point". Second order would be a quadratic, etc.

The schema allows only positive integers for the @order attribute. This should be non-negative integer.

Update the data type for the @order in Spline Calibrators

Proposed is to change the numeric type of the @order in the SplineCalibrator element. The 1.1 definition for this attribute is:

<element name="SplineCalibrator">
<annotation>
<documentation xml:lang="en">A calibration type where a segmented line in a raw vs calibrated plane is described using a set of points. Raw values are converted to calibrated values by finding a position on the line corresponding to the raw value. The algorithm triggers on the input parameter.</documentation>
</annotation>
<complexType>
<sequence>
<element name="SplinePoint" type="xtce:SplinePointType" minOccurs="2" maxOccurs="unbounded"/>
</sequence>
<attribute name="order" type="positiveInteger" default="1"/>
<attribute name="extrapolate" type="boolean" default="false"/>
</complexType>
</element>

The change would update the following:

<attribute name="order" type="xtce:nonNegativeLongType" default="1"/>

Also add the possibility for the SplinePoint element to override the @order on the SplineCalibrator. This should be specified on the first point in a pair if desired for the pair itself to be treated as a different @order than the SplineCalibrator overall. This assures backwards compatibility and simplifies the most common use case. Here is the update SplinePointType with the new attribute.

<complexType name="SplinePointType">
<annotation>
<documentation xml:lang="en">a spline is a set of points from which a curve may be drawn to interpolate raw to calibrated values</documentation>
</annotation>
<attribute name="order" type="xtce:nonNegativeLongType" use="optional">
<attribute name="raw" type="double" use="required"/>
<attribute name="calibrated" type="double" use="required"/>
</complexType>