GIS

Another interest, though certainly not an area of expertise, is Geographic Information Systems and digital mapping. I had an old copy of DeLorme StreetAtlas for Macintosh, which only ran as a “classic” application. I also had GPSy for the Macintosh, which also has not been released for OS X yet, and hasn’t been updated in a long time. I’d like to learn the GRASS GIS application once I have time to get it configured. GRASS is a very powerful, open source GIS package, comparable to ESRI ArcInfo in terms of features and capabilities. It can run on either my FreeBSD or Linux machines or on Mac OS X. I have also used ESRI ArcExplorer, a lightweight GIS data viewer developed by ESRI. This freely available software offers an easy way to perform basic GIS functions to display, query, as well as data retrieval. It supports a wide variety of standard data sources, and is available as a Java application on a variety of platforms. I have had it running it on both Mac OS X and FreeBSD (Using the Linux installer). I still have an old Garmin GPS III receiver that I used when off-roading, camping and hiking. It has built-in maps with sufficient detail for highway driving, and creates its own “bread crumb” trail to follow back when off-highway. There is also a serial interface that can connect the GPS to a computer (with a string of adapters) so that mapping software can read the coordinates from the receiver. Some time […]

Introduction: One of the side-effects of “wardriving” to detect the locations of wireless access point (WAP) using a mobile device such as a laptop computer with a GPS is that all of the locations of the WiFi hotspots all appear on a map at the location where they were detected, not where the source of the radio signal originates. This generally means that all of the mapped locations of detected networks are marked in the middle of a street. Theorum: The geographic location of a wireless access point (WAP) can be approximated by recording the GPS coordinates and signal strength in three or more locations. The point of origin can then be calculated using trilateration. To optimize efficiency for use with a mobile device such as a smartphone, use of a simple algorythm to capture four points, corresponding to the minimum and maximum latitude and longitude coordinates where the signal from the WAP can be conveniently measured. Assumptions: The maximum signal range of a typical commercially produced, consumer-grade wireless access point is roughly 300 ft or 100m. Since most commercial wireless equipment is provided with an omni-directional antenna, its assumed that the radio signal radiation pattern can be expected to be roughly circular. While buildings and terrian can reduce the range of wireless signals, in a typical residential area the interference could be assumed to be roughly equal in all directions. Thus, it can be safely ignored when estimating the location of the access point. The radiated power of the