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SW1 Diagram

Reproduced from 1954 diagram book

Throughout its history, the CofGa produced locomotive diagram books that were distributed to shop personnel. In the days of steam locomotives, when many parts were crafted by hand, diagram books documented the multiple configurations that shop personnel might face when servicing or repairing the company's motive power. By the time the Central started buying diesel locomotives manufacturers had mostly settled on standard designs using interchangeable components, and the days of making replacements parts in the company shops were over.

	Internet Explorer 5.0 or higher: Follow this link to diagram
SW1 Diagram. CGRHS Image / Ron. Wright

A diesel diagram book lists each type of engine the company owned at the time the diagram book was issued. For each locomotive type, the book shows a diagram and lists the road numbers of engines of that type operated by the company. Other data might also be provided, such as operating weight, fluid capacities and specific component types.

Rendering these diagrams in a Web friendly way is challenging. The simplest solution is to scan each page and publish it in a format understood by browsers, such as JPEG or GIF. The problem with this approach is that preserving the resolution of the original images creates files that are very large by Web standards. Few people have Internet connections fast enough to allow them to conveniently download megabyte size files. Large files also use up the storage capacity allocated by an ISP.

An emerging standard for document sharing, called Vector Markup Language, or VML, offers a solution. VML encodes individual lines and strokes of a diagram in a format that can be compressed into a much smaller size file than a corresponding image file would be. This is because a VML file stores the list of commands required to render a drawing, which might resemble "MoveTo (0,100). DrawTo(200, 200)" instead of the pixels themselves.

A VML document can be zoomed to any arbitrary degree. The default range supported in VML documents created using Visio is "Fit to Window" and from 25% to 1200% zoom.

Rendering a diagram in VML can result in a loss of subtle detail. For example, a drafting technique called "feathering" involves changing the pressure applied while drawing a line to cause local variation of the resulting line width. A drawing program provides a fixed number of pen widths and feathering is not easily replicated.

Creating a high-fidelity VML diagram is time consuming. Adding more detail means spending more time.

Perhaps the biggest problem associated with VML is that only Microsoft Internet Explorer Version 5.0 or higher supports it. VML is a standard built on XML, and while the World Wide Web Consortium (W3C) defines and promulgates both of these as international standards, so far only IE supports them. Support on Windows machines is best.

Site visitors with Internet Explorer 5.0 or later can follow this link to view a VML diagram of an SW1 locomotive from a 1954 diesel diagram book. Other browsers will be given a medium-quality GIF file to render. The GIF cannot be zoomed.

The Central of Georgia Railway HS Web site has been selected as a featured site by StudyWeb, an Internet site for educational resources for students and teachers.

This Web site is maintained by Ron Wright

Revised: Copyright © Central of Georgia Railway Historical Society, Inc. All rights reserved.