My hobby involves photographing poops in the outdoors, then returning to the same sites in months or years, to see what has grown on the poops. Can I use a GPS to track the poop locations? I’m particularly interested in poops that are not near readily identifiable trails or features. Will the GPS be accurate enough?
I’m very glad you asked; the answer is not straightforward. I’ll assume that you are mainly concerned with horizontal (x,y) accuracy.
With the new, sensitive chipsets, the absolute accuracy of a hand-held GPS may be as good as +/- 10 feet. With an unobstructed view of the sky, and WAAS activated, the accuracy may be +/- 6 feet. However, many factors can degrade the accuracy. GPS is a tool with limits, and you should be aware of the limits.
First, if the view of the sky is obscured, and the unit sees just a small number of satellites, the accuracy can balloon to hundreds of feet; under dense tree cover, even newer units will typically have an accuracy of +/- 20-50 feet. The signals are microwaves, and the same things that alter or absorb microwaves in your kitchen, will affect the GPS. Clouds, falling rain, and snow generally DO NOT affect the accuracy greatly, as the water droplets are too small and dispersed, and frozen water has a different energy absorption band; but a wet case can significantly reduce the signal. Your head and body are also problematic; the GPS should be as high as possible when carried, and the best signals come when it is held away from you body. As discussed previously, reflections can be a problem, particularly when the unit is a few hundred feet from vertical high walls, or if your head is very dense. (Reflected signals are actually less of a problem if you are right at the wall.) In the worst case I’ve seen, reflections offset the signal by an apparent 100 feet. Always display the estimated accuracy on the GPS, and know the signs of error, such as sudden jags in the track when you have been moving consistently.
In your case, if the poops are not near a distinctive feature, the GPS may get you within 10-20 feet; but that may be a long ways in rough country. You would best photograph the poops or perhaps draw them in situ (pastel colors preferred), so you can do an exact relocation when you are within the circle of error.
In some places, an error of +/- 10 feet can be a serious problem, so never let the gadget overwhelm your common sense. For example, I often use the GPS to locate complex scrambling routes in Red Rock, NV. A horizontal uncertainty of +/- 10 feet can put me up or down one ledge, and the correct ledge may be 50 feet vertical above or below. If the GPS tells me to step 10 feet to the left, but there is a great big drop there, I’ll send my partner first (see “Plans and Partners: Trusting Types”).
WAAS is more battery-consumptive, and usually works only on fairly elevated terrains, or those with an unobstructed view of the southern sky (strictly speaking, WAAS only works in the US, but Europe and much of the rest of the world has something similar). The WAAS satellites are geosynchronous (and thus above the equator), and are generally not in view if you are in a canyon or north-facing slope. I leave WAAS turned off on my current unit.
I’d like to discuss relative accuracy, vertical accuracy, and time-averaging, areas where a simple GPS can do better, but that will have to another thread.
gosh you are so kind!
Yes, I am.