Re: serial comm with GPS, not quite an NMEA sentence
Re: serial comm with GPS, not quite an NMEA sentence
- Subject: Re: serial comm with GPS, not quite an NMEA sentence
- From: Sherm Pendley <email@hidden>
- Date: Tue, 3 Oct 2006 12:21:36 -0400
On Oct 2, 2006, at 11:58 PM, Gonzalo Castro wrote:
I'm learning how to get data from a serial device, specifically a
GPS set to use NMEA protocol. I came across the following sample
code, at http://www.harmless.de/cocoa.html#serialport.
The method below seems to be called when receiving data. Should I
expect the NSData *data to contain an NMEA formatted string? Eg,
"RMC,225446,A,4916.45,N,12311.12,W,
000.5,054.7,191194,020.3,E*68" (clipped from http://www.eoss.org/
pubs/nmeafaq.htm). If so, then I'm not getting such a string.
Instead, dataStr looks like garbage.
From the docs link above:
3.2 "Complex" data format
The complex format consists of a data block of 37 bytes of
(mostly) readable ASCII text giving cross-track error, bearing
to waypoint, present Lat/Long, and a binary status byte. The
data block shall be sent at intervals of 2 to 8 sec. All bytes
in the complex format have bit 7 = 1 to distinguish them from
the simple format.
Note that last sentence - what you get is almost but not quite ASCII
text, although it looks like it can be easily converted to ASCII.
You'll need to look for, and strip out if necessary, the high bits.
sherm--
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