Since its very beginning, EMME/2 has always had the capability to produce color graphic output, provided the installation was equipped with a color graphic terminal. However, the color model being completely independent from any specific terminal characteristics, color was always used only to enhance readability of the graphics, but never contained any information as such. This principle ensures that even on monochrome output the information contents is always complete.
Nowadays, more and more installations do have color terminals and multipen plotters. It is only natural that these users would like to do more with the added dimension of color than just distinguish elements of the plots. The color should also be able to convey additional information to complement the information contained in the geometry of the graphics. For example, a link volume bar plot could also incorporate information in the form of different coloring about the speed on each link, or the relative increase or decrease of volume compared to the base scenario, or any other pertinent data. Transit line itineraries, as produced by module 2.23, could be colored by vehicle type, operator, mode or any other criteria. As can be seen easily, there are many ways in which colors could be used to complement EMME/2 graphic output. It it just as clear that it is not possible to enumerate all these possibilities and implement them all individually. Implementing just some arbitrarily selected ways of coloring elements, on the other hand, would not be fair to the user.
The solution we adapted, and which is implemented on a test basis in module 6.12 "Plot Auto Volumes and Times", is based on a new general concept, the color index attribute. Instead of determining the color of a depicted element automatically, the user will have the choice of declaring one of its user data items as color index attribute. In this way, the user can individually define the color of each element that is plotted. While, by itself this feature is already quite useful, its power is multiplied manifold by combining it with the new network calculator, module 2.41 (see elsewhere in this issue for a detailed discussion of this new module). With this new tool, the color index can be calculated on the spot, based on any combination of network attributes or result values. The color index is a number that will be truncated to a positive integer at plot time. A value of 1 is always the primary color, i.e. white on terminal output, black on a plotter output. Color indices 2,3 and 4 correspond always to red, green and blue, respectively. Higher indices produce different distinguishable colors up to the number of colors available for the specific type of terminal being used. For higher indices, the colors will be repeated in the same sequence, always omitting the primary color. In order not to frustrate the user equipped only with monochrome devices by continuously asking him questions about color indices which are meaningless to him, the color index question can be activated or disactivated by means of a new module parameter. (On monochrome output devices, any color index will, of course, produce the primary color.)
In Release 2.0, this new concept has been introduced into module 6.12. The link bars may now be colored using a link user data item. If you wish to try out this new feature, do not forget to activate it first by answering "yes" to the corresponding question in the module parameters.
If the user response is favorable, color indices will be added throughout the system, i.e. in modules 2.13, 2.15, 2.23, 2.31, 3.13, 6.14, 6.15 and 6.22.