Thursday, September 07, 2006

Using a GPS to Discover Old Mills

How often have you been looking for an old mill and know you have to be very close but you just can’t located. I know in my searches this has happened numerous times. When I first started looking for old mills more than 20 years ago, I would purchase map books of a state which would have detailed county maps (these books are still available). Before going milling I would take the SPOOM (Society for the Preservation of Old Mills) mill list (The mill lists provide directions to mills and are usually very accurate.) and try to plot the location of the mills I was hoping to visit. Generally I was able to locate the mill that I was wishing to photograph, but several times I just could not find the mill. With the technological improvements in computer technology, I started using a GPS (Global Positioning Satellite) Receiver, a laptop computer and mapping software; I also needed a power inverter to power the computer from my cigarette lighter. The first couple generations of the software was somewhat limited, the GPS took a long time to link with the computer through the serial port and the laptop computers were relatively slow compared to our current standards, so map regeneration took a few seconds. Today I use a Bluetooth wireless GPS receiver that connects to my laptop computer. I also have a hand held GPS which connects to my PDA (Personal Data Assistant) by the compact flash slot. The same software can be loaded on both my PDA and laptop. When I locate a mill I create a waypoint for the mill and potentially other components around the mill like the mill dam, race and other structures. Therefore the GPS shows my position but in general does not locate the mill for me since no one as recorded its position, but instead I use the GPS to locate the position of the mill that can be used by others. Some of the software packages will show elevations on the map and some will show the old mill ponds which can assist in the locating of the mill. For a few of the mill someone else has geocoded (latitude and longitude) the position and that can be programmed into the software and which will determine the shortest or quickest route to the mill from any starting position. Therefore, by using a GPS we can position the mill to a high degree of accuracy so that future generations will have the pleasure of locating these wonderful structures. Hopefully people will share there mill positions so that it will become easier to locate the mills, much as was done in the creation of the mill lists. SPOOM mill list do have a fields for latitude and longitude.

A GPS receiver works by measuring the time that it takes for a signal to reach the receiver from multiple satellites orbiting the earth. By knowing the time for the signal from each of the satellites to reach the receiver, the distance to each satellite (the position of these satellites are very accurately known) can be computed and by using trigonometry your position on the surface of the earth can be determined in 3D, latitude, longitude and elevation. The more satellites that the receiver can detect the more accurate your position, most GPS units will be accurate to 30 feet or less. The accuracy of the GPS is dependent on the number of satellites and number of digits of accuracy that the unit can receive. Some of the units can also detect ground stations that have a position that is known to a high degree of accuracy and can further reduce the position error. A GPS is only a receiver unless it contains a cell or satellite phone, many trucking companies utilize GPS technology and a satellite phone to determine the position of their trucks at all time. Therefore, the home office can locate every vehicle at any moment. A determination of the speed of an object can also be calculated, since the GPS is determining the position at regular interval of time, the accuracy of the speed determination can be as good as your speedometer.

If you looked at purchasing a GPS unit you know there is a whole range of devices and prices. The simplest type of GPS is the ones contained in many cell phones today (all new cell phones have a GPS), usually to utilize the GPS you must pay for a service. If you want to purchase a GPS unit there is a complete range of prices and abilities and I will try to describe some of the different types of GPS units. A completely standalone unit can be purchased and will vary in cost from a few hundred dollars to several thousand dollars depending on the abilities of the instrument. If you want a device to provide only the longitude and the latitude of your position they are relatively inexpensive. The next step-up is those GPS units that provide monochromatic maps of the region on the display. The more advanced system offer more detailed color maps. Some of these units can be connected to a computer so that you can download data and others the data must be manually recalled if you wish to plot it on a computer map. The second type of GPS utilizes as PDA like a Palm Pilot or a Dell Axiom. Maps can be loaded into PDA from a computer and can either be directly connected to the GPS via cable, PCMCIA Card, Compact Flash Slot or by Bluetooth wireless. These units are small and more expense than the low end standalone GPS, but much more flexible since they can be connected directly to a computer and maps can be upgraded as changes occur. They also retain the function of the PDA. The third method is to use a GPS either directly connected to your laptop computer by a USB cable or wireless connection. These devices are the most flexible and provide the most power to the user, but also the most expensive unless you are already have the laptop computer. Of course we also have GPS units in some cars.

With most all GPS units you have the ability to store a position and name the position that is stored, like Pierce Mill Dam. These positions are called waypoints. The position of the mill, the dam, the race can all be stored within the accuracy of the device (30 feet or less) as was discussed above. This geocoding of the position of dams can than be placed into a GIS (geographical information system) system and stored on maps that can be displayed over the internet, with roads and other major features labeled.

So instead of missing that mill that was just around the corner in the overgrown field we can find the location every time if someone provides the accurate latitude and longitude of the mill. In most GPS you can put in the position that you want to locate and it will direct you either by displaying directions and distances away from the point, or on more expensive systems it will display the roads and directions of each turn to reach the site and the upper end systems will map it for you displaying your current position, your end point, display the roads, giving directions, even speak to you when you need to turn and if you get off the road it will reroute you. Of course every once in a while the computer map is not correct, most of these maps were developed from either aircraft imagery or satellite data. I was recently searching for a mill in the Catskills in New York state and the road in which the computer told me to take to reach the mill that I had (from looking at a website) did not reach the mill, about half way up a mountain the road became a dirt path, so every once in a while technology can fail you.

For the last several years I have been geocoding the mills sites that I have visited and will be in the near future placing them on an interactive website for others to use. If anyone would like to send me the locations of mills I will be happy to add them to my data. I can be reached at

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