[Loadstone] Question about Accuracy
rob at loadstone-gps.com
Tue Feb 27 23:59:35 GMT 2007
Here's a table that can be used while reading key 2 - accuracy in Loadstone
(from a car driver's point of view):
This is the highest possible confidence level to be used for applications
demanding the highest possible precision at all times.
At this confidence level, positional measurements are considered accurate
enough to meet all but the most sensitive applications.
Represents a level that marks the minimum appropriate for making business
decisions. Positional measurements could be used to make reliable in-route
navigation suggestions to the user.
Positional measurements could be used for calculations, but the fix quality
could still be improved. A more open view of the sky is recommended.
Represents a low confidence level. Positional measurements should be
discarded or used only to indicate a very rough estimate of the current
At this level, measurements are inaccurate by as much as half a football
field and should be discarded.
For pedestrian use 4 is as worse as you want it to get. More on similar
issues, as well as this table, can be found at:
At 2/27/2007, you wrote:
>On Tue, Feb 27, 2007 at 01:32:34PM -0800, Tom Lange wrote:
> > Keypad 2 shows 2.6.
> > Often I've seen numbers as low as 1.0, 1.1, 1.2, and so on. What do those
> > numbers represent? Are these numbers on a scale of 1 to 10, for example,
> > where 10 represents the highest possible accuracy?
>What Loadstone calls accuracy is actually called HDOP or
>horizontal dilusion of precision. Put simply it's an error
>factor which is based on the accuracy of the GPS device.
>In other words, the hdop can vary for the same accuracy
>given two gps devices with different unenhanced precisions.
>A rough idea of accuracy can be had by multiplying the hdop
>by the accuracy of the device. For example, the sirf3
>units have a stated positional accuracy of 10 metres so an
>hdop of 2.6 means you should be within 26 metres of your
>target. If you are getting waas corrections, the hdop can
>go below 1 to let's say 0.8 giving an accuracy of 8 metres
>on a 10 metre precision unit. hdop can go as high as it
>likes but I wouldn't trust anything above 5 for pedestrian
>use on a Sirf3.
>Loadstone mailing list
>Loadstone at loadstone-gps.com
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