On Tue, Feb 9, 2010 at 2:28 PM, Norman Vine wrote:
>
> On Feb 9, 2010, at 3:14 PM, Curtis Olson wrote:
>
> Notice you are only getting 6 decimal places on your lat/lon and I know
> from a past life that this will probably resolve down to a resolution of
> maybe 10-20 meters.
>
>
>
> Hmm
>
> 6 decimal places should get you sub meter precision
>
> http://manisnet.org/GeorefGuide.html#imprecision_in_coordinates
>
Ok, I'll agree with that. I think the problem in this case is that the
protocol.xml file specifies an output type of <float>. This is essentially
doing the following:
float lat = lat_node->getFloatValue();
printf("%f", lat);
So even though we are seeing 6 decimal places of data being printed, only
the first 6-7 actual digits are useful, so let's say we get a full 7 digits
of precision, a number like -122.123456 really is only good to -122.1234 (7
total digits irrespective of the decimal place ... the definition of the
word "floating point" in "floating point".) That gives us about 0.0001
accuracy which equates to about 15m of uncertainty according to your link.
Regards,
Curt.
--
Curtis Olson: http://baron.flightgear.org/~curt/
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