Introduction... Many years ago, on thin-wire network, when 40MHz
SPARC processors were state of art, I was involved in a project
to integrate digital raster maps with other digital information,
replacing a cumbersome paper and grease pencil process. The heart of
this project was the Map Display Server, which wedged itself between
the client applications and the X11 server.
Fast forward... to today. One of my favorite resources on the Internet is the online library of historical topographical maps at the Univerisity of New Hampshire. Today, we also have Global Posistioning Satillites, which can locate you within 30 feet or so. I needed a way to merge the historical maps with the modern GPS technology to assist with various research projects. The solution was to write a much simplified application, and the mini Map Display Server, aka mMDS, was born.
Simple.. is good. The mMDS only does a couple of things; first and foremost it displays the maps, which are scanned as JPEG files. Second, based on several known points, it translates back and forth between the X11 (x,y) cordinate system, and the familar longitude and latitude system. And third, it maintains a Phigs-like queue of objects. Client applications request which maps to display, and what objects to draw. A simple, text based, TCP connection is used to communicate between clients and the mMDS. You can even use telnet to control the map display!
Initial testing... has included a GPS-driven moving map display which the kids and I have tested by driving around the state. In this case, data from the GPS was read by Chuck Taylor's NMEA Server (aka "nmead"), and then passed to mMDS as a series of "Recenter" commands. Defining and drawing pixmaps is also supported.
More... to come. Source code will be released, plus a description of the protocol. Support for primative points, lines, and polygons is planned.
Disclaimer... None of the source code from the original project was re-used, and in fact, I wasn't involved in the design or implementation of the original server. I have had access to several engineers who did write the original server, and they have been helpful in answering some of the "why" questions that I have pondered over while writing my own implementation.
For more information, contact me by email.