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Discussion of precise time and frequency measurement

Survey plot as art.

Mark Sims

Mon, Jan 9, 2017 3:41 AM

The Thunderbolt has a command for entering the receiver position, but it uses 32-bit floats. This restricts the accuracy that you can enter a position. Lady Heather's precision survey routines can calculate a position to greater accuracy. In order to save the high-accuracy calculated position it uses the rather nasty technique of doing single-point self-surveys until one happens to be within a foot or so of the calculated position.... that can take an indeterminate amount of time to happen, but eventually gets the job done.

The Adafruit plot seems to have quantization. Are the values being

"snapped" to a grid in any way?

The Adafruit receiver outputs NMEA format data. The lat/lon values are sent as dddmm.mm format (ddd=degrees, mm.mm=minutes) This restricts the resolution of the values. Some receivers and newer NMEA specs support more digits past the decimal point. Receivers that support native binary formats that report lat/lon as 32-bit floats show similar quantization. The Thunderbolt has a command for entering the receiver position, but it uses 32-bit floats. This restricts the accuracy that you can enter a position. Lady Heather's precision survey routines can calculate a position to greater accuracy. In order to save the high-accuracy calculated position it uses the rather nasty technique of doing single-point self-surveys until one happens to be within a foot or so of the calculated position.... that can take an indeterminate amount of time to happen, but eventually gets the job done. ----------------- > The Adafruit plot seems to have quantization. Are the values being "snapped" to a grid in any way?

Gary E. Miller

Mon, Jan 9, 2017 4:14 AM

Yo Mark!

On Mon, 9 Jan 2017 03:41:07 +0000
Mark Sims holrum@hotmail.com wrote:

Yes, easy to see the quantization in the Adafruit plot.

RGDS
GARY

Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
gem@rellim.com Tel:+1 541 382 8588

    Veritas liberabit vos. -- Quid est veritas?
"If you can’t measure it, you can’t improve it." - Lord Kelvin

Yo Mark! On Mon, 9 Jan 2017 03:41:07 +0000 Mark Sims <holrum@hotmail.com> wrote: > The Adafruit receiver outputs NMEA format data. The lat/lon values > are sent as dddmm.mm format (ddd=degrees, mm.mm=minutes) This > restricts the resolution of the values. Some receivers and newer > NMEA specs support more digits past the decimal point. Receivers > that support native binary formats that report lat/lon as 32-bit > floats show similar quantization. Yes, easy to see the quantization in the Adafruit plot. RGDS GARY --------------------------------------------------------------------------- Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703 gem@rellim.com Tel:+1 541 382 8588 Veritas liberabit vos. -- Quid est veritas? "If you can’t measure it, you can’t improve it." - Lord Kelvin