STUMTA - Given the coordinates of a point on the streamline in data, user, and NDC space, and the interpolated, normalized components of the vector at the point relative to data coordinate space, the user- modifiable routine STUMTA finds the directional angle of the streamline relative to NDC space at the point.
CALL STUMTA (XDA,YDA,XUS,YUS,XND,YND,DU,DV,TA,IST)
XDA (REAL, input): The X coordinate of a point on the streamline in the data coordinate system. YDA (REAL, input); The Y coordinate of a point on the streamline in the data coordinate system. XUS (REAL, input): The X coordinate of the point in the user coordinate system. YUS (REAL, input): The Y coordinate of the point in the user coordinate system. XND (REAL, input): The X coordinate of the point in NDC space. YND (REAL, input): The Y coordinate of the point in NDC space. DU (REAL, input): The interpolated value of the normalized component of the vector at the point, with direction parallel to the X axis of the data coordinate system. DV (REAL, input): The interpolated value of the normalized component of the vector at the point, with direction parallel to the Y axis of the data coordinate system. TA (REAL, output): The directional angle of the streamline at the point relative to NDC space. IST (REAL, output); Status of the mapping operation: 0 indicates success, negative values indicate that the mapping failed; positive values are reserved and should not be used by the implementor of a mapping routine.
STUMTA is a user-modifiable routine provided to support custom mappings of the data coordinate space. The user does not invoke it directly. Instead, whenever the parameter MAP specifies a mapping not handled by Streamlines internally (i.e., when MAP is set to a value other than 0, 1, or 2), Streamlines calls STUMTA once for each incremental step in the creation of a streamline. The default version of STUMTA simply returns the angle implied by the incremental vector components passed to it: that is, it returns ATAN2(DV,DU). In order to implement a custom mapping, you must pick a unique mapping code (a positive integer greater than 2), and then modify each of the three routines, STUMXY, STUIXY, and STUMTA to recognize and respond consistently to the chosen code. In the standard distribution of NCAR Graphics, these three routines reside in a single file, stumxy.f. STUMXY maps a point from data to user coordinate space and STUIXY inversely maps a point from user to data coordinate space. STUMTA, which is likely to be the most difficult to implement, finds the tangent angle of the streamline at a point in NDC space. STUMTA has access to a common block called STMAP that contains a number of variables used to record the current transformation state. In order to accommodate a variety of mapping implementations, STMAP provides more information than normally required. Consider the values stored in STMAP as strictly read-only. One essential member of this common block is IMAP, which contains the value currently assigned to the MAP parameter. When implementing a non-linear mapping, an iterative differential technique will most likely be required. Look at the routine, STMPTA, in stmpxy.f, which handles the pre-defined mappings, for examples of the method. Both the default transformation (MAP set to 0), in order to account for possible log scaling of the user coordinate axes, and also the Ezmap projection (MAP set to 1) use such a technique. Basically the idea is that the vector components must be proportionally reduced in size enough that an effectively "instantaneous" angle can be calculated, although they must not become so small that the calculation is adversely affected by the floating point precision available for the machine. Additionally, checks must be put in place to prevent the increment from stepping off the edge of the coordinate system space. The pre-defined mappings step in the opposite direction to find the angle whenever an increment in the original direction would fall off the edge.
To use STUMTA, load the NCAR Graphics libraries ncarg, ncarg_gks, and ncarg_c, preferably in that order.
Online: stgetc, stgeti, stgetr, stinit, stream, streamlines, streamlines_params, strset, stsetc, stseti, stsetr, stuixy, stumsl, stumxy, ncarg_cbind. Hardcopy: NCAR Graphics Fundamentals, UNIX Version
Copyright (C) 1987-2009 University Corporation for Atmospheric Research The use of this Software is governed by a License Agreement.
Personal Opportunity - Free software gives you access to billions of dollars of software at no cost. Use this software for your business, personal use or to develop a profitable skill. Access to source code provides access to a level of capabilities/information that companies protect though copyrights. Open source is a core component of the Internet and it is available to you. Leverage the billions of dollars in resources and capabilities to build a career, establish a business or change the world. The potential is endless for those who understand the opportunity.
Business Opportunity - Goldman Sachs, IBM and countless large corporations are leveraging open source to reduce costs, develop products and increase their bottom lines. Learn what these companies know about open source and how open source can give you the advantage.
Free Software provides computer programs and capabilities at no cost but more importantly, it provides the freedom to run, edit, contribute to, and share the software. The importance of free software is a matter of access, not price. Software at no cost is a benefit but ownership rights to the software and source code is far more significant.
Free Office Software - The Libre Office suite provides top desktop productivity tools for free. This includes, a word processor, spreadsheet, presentation engine, drawing and flowcharting, database and math applications. Libre Office is available for Linux or Windows.
The Free Books Library is a collection of thousands of the most popular public domain books in an online readable format. The collection includes great classical literature and more recent works where the U.S. copyright has expired. These books are yours to read and use without restrictions.
Source Code - Want to change a program or know how it works? Open Source provides the source code for its programs so that anyone can use, modify or learn how to write those programs themselves. Visit the GNU source code repositories to download the source.
Study at Harvard, Stanford or MIT - Open edX provides free online courses from Harvard, MIT, Columbia, UC Berkeley and other top Universities. Hundreds of courses for almost all major subjects and course levels. Open edx also offers some paid courses and selected certifications.
Linux Manual Pages - A man or manual page is a form of software documentation found on Linux/Unix operating systems. Topics covered include computer programs (including library and system calls), formal standards and conventions, and even abstract concepts.