This was quite a long section giving a great deal of detail of individual routines. We have included here just the introductory sections to give an idea of what it contained.
This part of the graphics manual contains chapters on associated groups of routines. Each chapter covers one particular area of graphics for which high level routines are provided in the RAL graphics system. The definition of 'high level' is rather difficult but in general terms it covers those facilities that are
The use of high level routines allows the user to concentrate on the form of output he requires and worry less about its production. As will be seen from the size of Part D, the Rutherford Graphics System contains a large number of high level routines. Many of these are adopted from standard routines that have been evolved over many years by people all round the world.
Each chapter deals with one particular topic: this organization (rather than say an alphabetic structure) has been used so that people wanting to use some existing routines have a reasonable chance of finding them and understanding how to use them. Each of the chapters is independent.
Chapter D2 deals with graph and histogram drawing (2-dimensional data only). There are a large number of routines available in this area and many have been written at RAL. New users should be sure to read the introduction to the chapter before choosing any routine.
Chapter D3 deals with routines that display smooth curves passing through or near to user data points. These curve fitting routines have been developed at Rutherford. The method used is that of Splines under Tension.
Chapter D4 deals with the production of contour diagrams of 2-dimensional data on regular and irregular grids. The routines have been developed at Rutherford from standard contour drawing routines.
Chapter D5 contains details of a routine that displays 3-dimensional data as prism plots ('Manhattan skylines'). This suppresses the display of hidden lines and has full control of the angle and position from which the shape representing the data is viewed.
This chapter describes all the routines available in the Rutherford Graphics System which allow the user to plot 2-dimensional data. There are routines for line graphs, graphs of linked plotting symbols, histograms and graphs with error bars around plotting symbols. The routines come from a variety of original packages and the structure of the chapter reflects this.
Section D2.2, referring to the DRPLOT package, gives details of the simpler options for drawing graphs, histograms and error bar diagrams. While the calling sequences for these routines have been kept as simple as possible, the output produced has been made as good as the device allows the more complex options allow the user to control the format of the output but not necessarily to improve the quality of the output.
Section D2.3 deals with the options which allow the user to produce more complicated graphs, including overlaying multiple graphs and changing the options for labelling the graph. It also gives details of options associated with the package that are not particularly linked to any plotting routine, such as the type of frame drawn, the positioning of tag marks along the axes and the superpositioning of graticules on the frame.
There are three main user callable curve fitting routines, FVCURV, CPCURV and OPCURV, which use the method of Splines Under Tension (Scalar and Planar- Valued Curve Fitting Using Splines Under Tension A K Cline, Comm. ACM. April 1974, Vol 17, No 4 p128). The purpose of this method is to imitate the fitting of cubic splines, but avoid spurious points of inflection that may occur.
Each of these routines is used for curve-fitting in different circumstances:
The first routine, FVCURV, is intended to plot a single-valued function that assumes values y(i) at abscissae x(i) (ie FVCURV fits a curve through Functional Values).
The second routine, OPCURV, is used in the more general situation, where it is required to pass a curve through a sequence of points (x(i), y(i)) in the plane. (ie OPCURV is used for Open Planar curves). In practice, the main difference between FVCURV and OPCURV is that OPCURV is capable of handling a multi-valued function.
The third routine, CPCURV, solves a similar problem to OPCURV, but for a solution curve that is closed. (ie CPCURV is for Closed Planar curves).
All three routines are capable of producing a solution curve composed of either dots or dashes, as well as a continuous curve.
A contouring package is available, consisting of two user level routines (CNTR2A, CNTR2B) for the production of contour maps of a surface, for which the heights are given at the points of a mesh. CNTR2A is used for contouring over a (possibly skewed) regular rectangular mesh. CNTR2B is used for contouring over a (possibly skewed) irregular rectangular mesh. Within each of the routines a number of options concerning the drawing of the map are available. These allow for a choice of two methods of contouring over the grid, user specified or routine calculated heights, specification of the angle between the axes of the grid, and various options concerning the layout of the map, labelling of the contours and distinctions between the contours. However, as these are available via a common block, the user need only specify those options required (if any) which are different from the default set. Only those items of data which are necessary for a contour map are supplied as arguments to the routines.
A Fortran routine called HIST3D is available which draws a three dimensional histogram.
Data is supplied to the routine as a two dimensional array of values. The three dimensional histogram is drawn as a set of rectangular columns (pillars) whose bases form a rectangular grid and whose heights are proportional to the values of the corresponding array elements. It is drawn using a perspective projection with hidden line removal. Scaling factors for the histogram may be specified as well as horizontal and vertical viewing angles and the viewing distance.
The routine is a modified version of SCAT3D written by John Barlow (Bubble Chamber Group, Rutherford Laboratory).
