Most consumer GPS devices these days will advertise that they have an accuracy of about 2 meters (6 feet), but if you’ve ever imported your position and compared it to a known location you’ll quickly realize that your data collection is not the stated accuracy of your device all of the time.
There are a couple of settings on most devices that you can adjust which will allow you to collect more accurate data. You can usually set your device precision by telling it to throw away or ignore information that is not within a user-set range of accuracy. The two settings that you would adjust are the VDOP and HDOP tolerance values.
VDOP - Stands for Vertical Dilution Of Precision. The higher the VDOP value the more diluted or inaccurate your data becomes.
HDOP - Stands for Horizontal Dilution Of Precision. As with VDOP the higher your HDOP value the less accurate your positional information.
By telling your GPS device to ignore data collection until a lower HDOP and VDOP value is achieved you will collect more accurate positional data. After adjusting these setting you may notice that your time to first positional fix takes a bit longer than when you allowed your device to collect data with higher VDOP and HDOP values - this is normal and it is the price of accuracy.
You may also find that in areas where satellite communication is difficult (mountainous terrain, dense forrest) that you never achieve a positional fix or that you have to wait for one or two minutes before you can achieve one - again this is a normal side effect of asking your device for more precision.
Assess your own situation and the accuracy of data that you would like to collect and adjust your settings accordingly.
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February 5th, 2008 at 7:23 am
I always wondered what those things were.
Thanks.