LaWGS

From NASA TM 85767:
The Langley Wireframe Geometry Standard is a format for describing configuration geometry with discrete points. These points are coordinates of the locus of points for contour lines over the configuration. In the LaWGS context,a contour line can be thought of as a set of points that when connected by straight lines will follow the contour of the object. Additionally, when respective points on all adjoining contour lines of the object are similarly connected, the mesh or wireframe object is created. Thus a LaWGS file consists of coordinates of the sets of contour points that are the nodes for this wireframe structure (see Figures 1, 2, 3, and 4).

A configuration, as defined in LaWGS, may consist of a single object or a collection of objects. The description of each object is identical in form to that of the others and as previously mentioned consists of sets of discrete points that define contours over the object. The order in which these object contours and their points are listed is not specified by LaWGS, but is a choice of the person who creates the LaWGS description. However, to insure that the LaWGS file will be interpreted correctly, consistency should be observed. For example, if the points of the first input contour of an object are arranged along the x-axis in increasing order (i.e., fore to aft), then each subsequent contour for the object should be defined in like manner. If the next contour listed for this same object is clockwise from the first contour, then likewise the third contour should be clockwise from the second, the fourth from the third, and so on for the remainder of the object. The key consideration when creating a LaWGS file is to maintain consistency, particularly in applications where differentiating between the interior and exterior of the wireframe model is important. For these applications where the direction of surface normal vectors must be considered, guidelines for ordering points are provided in Appendix C.

Each object may be defined in either of two ways: 1) relative to a global coordinate system that exists for the configuration or 2) relative to its own local coordinate system, i.e., independently of the other objects in the configuration. Both the global and the local coordinate systems used in LaWGS are right-handed Cartesian coordinate systems. The x-axis corresponds to the longitudinal axis of the vehicle positive from nose-to-tail; The z-axis is usually vertical, positive upwards, and the y-axis is positive in the right-wing direction. For objects described in the global coordinate system only, the LaWGS file will contain an alphanumeric identification of the configuration and an alphanumeric identification of each object, an integer identification number which is unique to each object, the number of contour lines to be listed for each object, the number of points to be listed for each contour line (note: every contour line on the object must have the same number of points), and the point coordinates of the object. The global symmetry parameter can be used to indicate symmetry about one of the three global axis planes. For objects described in local coordinate systems, additional parameters are provided to locate the object relative to the global coordinate system. The local symmetry parameter can be used to indicate symmetry about one of the three local axis planes. Also, the object may be rotated, translated, and scaled to achieve its desired orientation in the global system relative to the other objects. The orientation of an object depends on the order in which the transformations are applied. In LaWGS, object transformations are applied in the following order:

1. local symmetry
2. rotation about the x-axis, rotation about y, rotation about z.
3. translation in x-direction, translation in y, translation in z;
4. scale in x-direction, scale in y, scale in z;
5. global symmetry.

Data is entered into a LaWGS file in list-directed format which complies with the American National Standards Institute (ANSI) FORTRAN 77 language described in document X3.9-1978. List-directed input/output processes coded data without a FORMAT statement. The input data values are free-form with separators rather than fixed-size fields. Separators can be one or more blanks, commas, or slashes, any of which can be preceded or followed by any number of blanks. Character strings must be enclosed in single quotes. The standard format is presented in the following section.

THE LANGLEY WIREFRAME GEOMETRY STANDARD (LaWGS) FORMAT