There are a wide variety of hardware centric features that can be found on GPS handhelds. These include barometric altimeters, electronic compasses, short-range wireless transceivers, temperature sensors and zoom cameras. All of these can be used to build your own portable and transferable geographic information system.
For the building of photonavigation systems, most GPS devices automatically geotag every picture taken. When you snap a photo, the GPS coordinates are stored along with the photo in GPS memory. Other data can also be stored with the picture: time, the weather conditions and your own notes about the photo shoot. The pictures than can be viewed in a picture viewer and then transferred to your PC, to another GPS device on your short-range wireless network, or to your long-range wireless cell phone. And some very advanced GPS systems enable pictures to be transmitted over satellites, anywhere and anytime.
The primary specification given for GPS cameras is pixel resolution, often measured in megapixels. In general, the higher the pixel resolution, the higher the picture quality. GPS cameras also offer lens zoom functions measured in terms of relative magnification. Most are rated at 4x multiplication.
Today’s GPS devices have as much as 4 GB of flash memory. However, because of the all the preloaded software stored in memory, there isn’t much memory left to store pictures or GIS data.
The compasses in GPS units are solid state. That is they can be turned on or off with a switch. Being that they are solid state, they are subject to interference from electronic signals. A noisy motor could affect an electronic compasses’ reliability. Before you use your compass, you will also have to make sure you calibrate it correctly. GPS handhelds include calibration menus for this purpose.
The compasses’ micromachine sensor most often has either two or three axes. The three-axis compasses have tilt compensation. Tilt compensation makes it much easier to use your electronic compass. With tilt compensation, you don’t need to tilt and stabilize your GPS unit to get an accurate heading.
The specifications to look at for electronic compasses include heading accuracy, resolution and repeatability. But many vendors just give degree accuracy and that can be very high, up to 5 degrees.
Besides the virtual compass your GPS displays, the trip computer display or page will also display your heading along with your speed, the number of miles to your destination and the estimated time of arrival. On some models it will also display your average speed, maximum speed and elevation. It will also display altimeter and elevation readings and calculations. The trip computer will display your elevation, the relative atmospheric pressure, and your rate of ascent or descent.
GPS altimeters often take some time to get used to. And that’s because they, like the electronic compass, must be calibrated first. Additionally, they have several modes of operations. In elevation mode, they will use GPS coordinate data and stored map data to approximate your elevation. In barometric pressure mode, the GPS unit will use relative pressure to determine your altitude.
Because atmospheric pressure varies with both elevation and weather conditions, the use of an altimeter requires the establishment of an altimeter reference point. This could be sea level or any other standard you decide. If you’re using the altimeter’s atmospheric pressure measurements for weather analysis, you must recalibrate it when you relocate it. Altimeters are usually stationary, or nearly stationary, when used for weather analysis.
Temperature sensors on GPS handhelds can be problematic. To measure the air temperatures do not hold the GPS unit. The heat of your hand will raise its temperature. For accurate temperature readings place the GPS unit in shaded area, not direct sun. Also keep it out of the wind, unless you want to determine the wind chill factor.
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