Subject: RE: TriWaco Triathlon : Official Thread dblack1801 - 2009-07-28 12:34 PM
so how, in this day and age of hand-held GPS units, is the swim course not set correctly? (and how did they do it before all this technology?)
I work in the GIS/Mapping field and also map out and measure ultra running courses and I can tell you that I NEVER rely on the distance I get from my GPS unit. I only use the data collected from a GPS to show the location of a course. For accurately measuring a course, I either use a bike calibrated to a measured distance or a Rolatape measuring wheel. For a GPS to be accurate, it needs a clear view of the satellites. If they are too low on the horizon or even too close together, then this ups the error in the GPS. There are also other factors that affect the accuracy, such as trees, buildings, bodies of water (i.e. a river ), people, etc. Also, how was the GPS set up? Was it set to collect a point every second, every three seconds, automatically (whenever the unit thought it was best )? Did the user move the unit around when collecting the points/tracks? There are just too many variables. I've been using my GPS and made a 180 degree turn and watched the accuracy go from 10 ft to over 20 ft. Now, the heavens may align and you end up with a somewhat accurate distance from the GPS, but this will be few and far between.
I sometimes use a Garmin 305 when I run, but it's more just to give me a GENERAL idea of pace and how far I went. I understand that both of these will be skewed a bit and I'm okay with that. If you understand the limitations of a GPS, then you are golden. But just don't count on it as showing the absolute correct distance. There's a reason why people that certify run courses don't use GPS. |