Originally Posted by
njkayaker
Note that a "handheld" GPS doesn't work any differently than the ones desgined for "vehicle" use (ie, ones designed for navigation use in cars.
No argument. But there is a big difference in how the different products are used. A handheld unit for field use has no navigation, so you wouldn't want to use it in your car. Likewise, a handheld GPS isn't optimized for bicycle use.
The problem with any of them is that they don't work very well at registering speeds at low speeds (this ends up not really being a problem for cars, because they are relatively fast).
Agreed, they don't work well at low speed. But speed has nothing to do with it. The issue is that GPS measures speed by measuring the difference in position. It does so at specific time intervals. So if you move in anything other than a straight line, the GPS will under-report your speed and distance travelled.
Anyway, the real problem with GPS-only altitude measurements is that the GPS system was designed to locate position on 2-dimensional surface because that was really the only goal. (Adding precise altitude measurements would have made the system much more expensive.)
No you're dealing with a 3-dimensional structure. Even if you use spherical coordinates, it's still a 3-dimensional system. I don't think the military would have forgotten that they have aircraft when they designed the system.
Actually, knowing the altitude is irrelevent for targetting missiles since it's generally good enough to be able to hit the ground that the target sits on!
The ground sits at a specific altitude. I'm pretty sure if the missle is flying too high, it will miss the target. It's a 3 dimensional system and the only reason it would not matter is if you dropped it from a standstill immediately above the target.
The Garmin Edge 705's one special feature is that it will display speed from a wheel-based transmittier by allowing the wheel size to be entered into the display unit. The other advantage of determining speed this way is that it doesn't need access to satellites and it is more accurate at low speeds.
Yes, cyclocomputers make better cyclocomputers.