14.4.7 ParametricLineArray

Topic Version1Published09/11/2015
For StandardRESQML v2.0.1

Defines an array of parametric lines of multiple kinds.

For more information, see the RESQML Technical Usage Guide.

In general, a parametric line is unbounded so the interpolant in the first or last interval is used as an extrapolating function.

Special Cases:

(1) Natural cubic splines with only two control points reduce to linear interpolation.

(2) If required but not defined, tangent vectors at a spline knot are calculated from the control point data using a quadratic fit to the control point and the two adjacent control points (if internal) or, if at an edge, by a vanishing second derivative. This calculation reduces locally to a natural spline.

(3) If not expected but provided, then extraneous information is to be ignored, e.g., tangent vectors for linear splines.


(1) Control points are (X,Y,-).

(2) Parameter values are interpreted as depth => (X,Y,Z), where the depth to Z conversion depends on the vertical CRS direction.

Piecewise Linear:

(1) Control points are (P,X,Y,Z).

(2) Piecewise interpolation in (X,Y,Z) as a linear function of P.

Natural Cubic:

(1) Control points are (P,X,Y,Z).

(2) First and second derivatives at each knot are inferred from a quadratic fit to the two adjacent control points, if internal, or, if external knots, by specifying a vanishing second derivative.

Tangential Cubic and Minimum-Curvature.

(1) Control points are (P,X,Y,Z).

(2) Tangent vectors are (P,TX,TY,TZ). Tangent vectors are defined as the derivative of position with respect to the parameter. If the parameter is arc-length, then the tangent vectors are unit vectors, but not otherwise.

(3) Interpolating minimum-curvature basis functions obtained by a circular arc construction. This differs from the "drilling" algorithm in which the parameter must be arc length.

Z Linear Cubic:

(1) (X,Y) follow a natural cubic spline and Z follows a linear spline.

(2) On export, to go from Z to P, the RESQML "software writer" first needs to determine the interval and then uses linearity in Z to determine P.

(3) On import, a RESQML "software reader" converts from P to Z using piecewise linear interpolation, and from P to X and Y using natural cubic spline interpolation. Other than the differing treatment of Z from X and Y, these are completely generic interpolation algorithms.

(4) The use of P instead of Z for interpolation allows support for over-turned reservoir structures and removes any apparent discontinuities in parametric derivatives at the spline knots.

Table 14.4.7-1 Attributes


Data Type




An array of explicit control point parameters for all of the control points on each of the parametric lines.

Described as a 1D array, the control point parameter array is divided into segments of length count, with null (NaN) values added to each segment to fill it up.

Size = count x #Lines, e.g., 2D or 3D

BUSINESS RULE: The parametric values must be strictly monotonically increasing on each parametric line.



An array of 3D points for all of the control points on each of the parametric lines. The number of control points per line is given by the KnotCount.

Described as a 1D array, the control point array is divided into segments of length KnotCount, with null (NaN) values added to each segment to fill it up.

Size = KnotCount x #Lines, e.g., 2D or 3D



The first dimension of the control point, control point parameter, and tangent vector arrays for the parametric splines. The Knot Count is typically chosen to be the maximum number of control points, parameters or tangent vectors on any parametric line in the array of parametric lines.



An array of integers indicating the parametric line kind.

0 = vertical

1 = linear spline

2 = natural cubic spline

3 = tangential cubic spline

4 = Z linear cubic spline

5 = minimum-curvature spline

(-1) = null: no line

Size = #Lines, e.g., (1D or 2D)



An optional array of tangent vectors for all of the control points on each of the tangential cubic and minimum-curvature parametric lines. Used only if tangent vectors are present.

The number of tangent vectors per line is given by the KnotCount for these spline types.

Described as a 1D array, the tangent vector array is divided into segments of length Knot Count, with null (NaN) values added to each segment to fill it up.

Size = Knot Count x #Lines, e.g., 2D or 3D

BUSINESS RULE: For all lines other than the cubic and minimum-curvature parametric lines, this array should not appear. For these line kinds, there should be one tangent vector for each control point.

If a tangent vector is missing, then it is computed in the same fashion as for a natural cubic spline. Specifically, to obtain the tangent at internal knots, the control points are fit by a quadratic function with the two adjacent control points. At edge knots, the second derivative vanishes.

Derived From: AbstractParametricLineArray

Derived Classes: (none)

Table 14.4.7-2 Relationships