Since the earliest versions of EMME/2, the limited national character sets for US, France, Germany, Great Britain, Sweden, Denmark and Spain have been integrated in the EMME/2 software character generator. This implementation is based on the 128 7-bit ASCII characters, the special national characters were substituting the US characters, depending on the font indicator of the corresponding device (bits 16-18 of the graphic device parameter, see manual III-2.7):
This method is standard for many mainframe systems, most stand-alone terminals and printers. However, it is not the method used on MS-DOS / PC-DOS systems. On PCs, an extended 8-bit character code is used to implement the special national symbols. This means that no US ASCII character is replaced, but the national characters have there own code in the range between 128 and 255. Besides the special national characters, this range also contains special mathematical symbols and line-drawing characters.
Unfortunately, the current version of the PLOTDEV driver (a product developed by Microplot Inc.) does not handle at all the extended 8-bit characters in graphic mode. As an additional complication, these extended characters are not displayed in text mode when the DOS-EDIT of PLOTDEV feature is activated. (Note that if this feature is not activated, the graphic input using the arrow keys refuses to work!).
From the above, it follows that, for an EMME/2 user working with a PC and a graphic PC monitor, it was up to now very difficult to access the special national characters of his country. While this did not affect the users in North America, it caused problems to many European users who depend heavily on these characters.
While it is beyond our influence to reprogram the PLOTDEV driver, we enhanced the EMME/2 internal software character generator in Release 4.0 to handle most of the national and mathematical extended characters. Note that the line drawing characters are not useful in the context of EMME/2 and, thus, are not supported. The following table shows the standard and extended characters which are supported in Release 4.0, together with their decimal representation:
These characters are now accessible without any change in the device table (i.e. bits 16-18 of graphic device parameter). Since this enhancement does not interfere with the old-style replacement scheme, the latter can still be used in parallel. In the above table, font 0 (US-ASCII) was used.
The new implementation offers the following benefits:
Since the software character generator which is built into the GPR utility
program has not yet been updated to handle the extended characters, it
will not always recognize these characters if they appear in plot
titles, transit line names and node labels. Annotations will always
work with GPR, since they
are vectorized within the EMME/2 system and thus never use the GPR character
generator. In order to make GPR fully compatible with the extended
characters, i.e. even in titles, transit line names and node labels,
the GPR device entry in
d002.in need to be modified by resetting to zero the
bits 4-7 of the graphic device parameter. Note that, unlike GPR, the GPL
utility is completely compatible with the extended character set and no
modification to the device table is needed.