Finding a Line of GPS data

[Ace Rimmer]

Hi, I'm able to read all the lines of data from a GPS module connected via usb, but I only want to see one or two of the lines..

Code: Select all

 import serial
 ser=serial.Serial('dev/ttyUSB0',9600)
 textln=ser.readline()
 while 1:
 	print (textln )
 	

All lines ( and there are many ) start with "$GP". How do I pick out the particular line I require ( $GPGGA) and print it?

[rpdom]

That code is wrong. It will read a line of text from the serial port, then print the same line over and over again for ever.

Try putting the ser.readline inside the while loop

Code: Select all

import serial
ser=serial.Serial('dev/ttyUSB0',9600)
while 1:
    textln=ser.readline()
    print (textln)

That's still a bit messy as it will keep trying to read lines forever. I don't use python much, it may be possible to do a "while(textln = ser.readline()):"

[ghp]

Hello,
you can check a line of code with string method startswith:

Code: Select all

import serial
ser=serial.Serial('dev/ttyUSB0',9600)
while 1:
    textln=ser.readline()
    if textln.startswith( '$GPGGA'):
        print (textln)

Good luck with your project !

[Ace Rimmer]

Thanks for the replies,
Long time no "see" Dom.
ghp - I'll try that code, it looks like it might do what I want. I'll let you know.

[rpdom]

Hi Ace

We have more spiders now. Some gone, some new ones.

[Ace Rimmer]

Thanks ghp that code does just what I wanted it to. I was a bit worried at first as I ran it from the Python shell and it returned an error (something to do with tuples or bytes) however when the py file was run from the command line it worked

So tell me Dom, what is the count now - reply in octal.

[rpdom]

So tell me Dom, what is the count now - reply in octal.

In octal the current count is 50. We're not adding to the collection at the moment, just concentrating on looking after the current ones.

We've got two old men who must be on their last (many) legs. They've lived a lot longer than expected for a mature male of those types.
Typically they get 6 to 18 months after reaching adulthood. These two have both survived over 3 years as adults so far.

[Ace Rimmer]

That's a lot of legs Dom. I think I know how the old ones feel! Just had great success with the above line of code that ghp supplied. I'm now able to pick out whichever NMEA sentence I require, turn it into a list and then pick out different elements (altitude etc).

Thanks again ghp

[Ace Rimmer]

OK, my next problem, this code works great

Code: Select all

 import serial

ser=serial.Serial(' /dev/ttyUSB0',9600)
while 1:
    textln=ser.readline()
    if ( '$GPGGA' ) in textln:
        listba=textln.split( ' , ')
        print ' your altitude is ',listba[9], ' metres above sealevel'

but instead of printing line after line I would like it to erase the line just printed and print it again with the updated value on the same line.
I'm using Python 2.7.* Any ideas?

[DougieLawson]

Try this technique to overwriting python output

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#!/usr/bin/python

import sys
import time

for i in range(0,101,10):
 sys.stdout.write("\r[%3d%%]" % i)
 sys.stdout.flush()
 time.sleep(1)

sys.stdout.write("\n")
sys.stdout.flush()

for i in range(0,10):
 sys.stdout.write("\rBlinking ...")
 sys.stdout.flush()
 time.sleep(0.5)
 sys.stdout.write("\r         ...")
 sys.stdout.flush()
 time.sleep(0.5)

sys.stdout.write("\n")
sys.stdout.flush()

The \r returns to the start of the line, the flush ensures the line is written to stdout.

[Ace Rimmer]

Thanks Dougie, I'll give it a try this arvo if the boss doesn't catch me. I gather I just use "sys.stdout.write" instead of "print", I haven't used that method before. Cheers.

[Ace Rimmer]

Yep, that worked - once I'd figured out how to concanate the components of the string - "print" is much easier! But oh for days of Qbasic with -

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locate (row,column)