Raspberry Pi Forums

Posted: **Thu Sep 07, 2017 7:56 pm**

I am in the midst of building a GPS/GNSS Rover for doing basic survey on my families farm. I've been looking at RTK and a really cool project for a base station and rover(Check it out here). I am currently looking for not only a less costly option, but also a few other features I don't see in this setup.

I saw this post and started with the first bit of python code to get me started.

Getting to the specifics of what I want;

The red box to stay centered on my position

To be able to load/open a file of coordinates that is then displayed as points on my screen

The blue box in the upper right will save my current location to a file. I would like to be able to load those points at a later date and go back to them.

My code as it stands today:

Code: Select all

#!/usr/bin/env python
import os
import pygame, sys
import datetime
import time
import math
import shutil
from pygame.locals import *
import serial
from decimal import *
getcontext().prec = 8

# initial values
Frame = 0
fix = 0
gps_con = 0
start = 0
lat = 0
lon = 0
speed = 0
angle = 0
oldX = 0
oldY = 0

# set screen size
width = 600
height = 500
Frame = 1

# set SCALE
J = 100000

#move old log.txt if exists
try:
   if os.path.exists('/run/shm/log.txt') == True:
      now = datetime.datetime.now()
      timestamp = now.strftime("%y%m%d%H%M%S")
      shutil.copy('/run/shm/log.txt','/gnss/logs/' + str(timestamp) + '_log.txt')
      os.remove('/run/shm/log.txt')
except OSError:
   pass
            
pygame.init()
blackColor =  pygame.Color(  0,  0,  0)
yellowColor = pygame.Color(255,255,  0) 
redColor =    pygame.Color(255,  0,  0)
greenColor =  pygame.Color(  0,255,  0)
blueColor =   pygame.Color(  0,  0,255)

if not Frame:
   windowSurfaceObj = pygame.display.set_mode((width,height), pygame.NOFRAME, 24)
else: 
   windowSurfaceObj = pygame.display.set_mode((width,height), 1,             24)
pygame.display.set_caption('GNSS Rover')

def print_text (msg,color,width,height):
    fontObj =  pygame.font.Font('freesansbold.ttf', height / 32)
    blackColor =  pygame.Color(  0,   0,   0)
    pygame.draw.rect(windowSurfaceObj, blackColor, Rect(0,height - (height/10),width,height - (height/10)))
    pygame.draw.rect(windowSurfaceObj, blueColor, Rect(width - 100,0,100,75))
    msgSurfaceObj = fontObj.render(msg, False, color)
    msgRectobj =    msgSurfaceObj.get_rect()
    msgRectobj.topleft = (width / 20, height - 30)
    windowSurfaceObj.blit(msgSurfaceObj, msgRectobj)

def fileplot(J):
   # replot coordinates when zooming in or out.
   q = 0
   oldX = 0
   try:
      pygame.draw.rect(windowSurfaceObj, blackColor, Rect(0,0,width,height))
      pygame.draw.rect(windowSurfaceObj, blueColor, Rect(width - 100, 0,100,75))
      pygame.display.update()
      with open("/run/shm/log.txt", "r") as file:
         while q < 9999:
            inputx = file.readline()
            inp = inputx.split(',',10)
            if q == 0:
               A = float(inp[3])
               B = float(inp[5])
            if q > 0:
               X = float(inp[3])
               Y = float(inp[5])
               pygame.draw.rect(windowSurfaceObj, yellowColor,Rect(((A-X)* J)+(width/2),((B-Y)*J)+ (height/2),3,3))
               if oldX != 0:
                  pygame.draw.line(windowSurfaceObj, yellowColor,  (((A-oldX)* J)+(width/2),((B-oldY)*J)+ (height/2)), (((A-X)* J)+(width/2),((B-Y)*J)+ (height/2)))
               oldX = X
               oldY = Y
               pygame.draw.rect(windowSurfaceObj, redColor,Rect((width/2)- 4,(height/2) - 4,10,10),1)
               pygame.display.update()
            q +=1
   except:
      pass

def plotpoint():
   now = datetime.datetime.now()
   timestamp = now.strftime("%y.%m.%d")
   with open('/home/pi/PointsFiles/' + str(timestamp) + '_pointlog.csv',  "a") as file:
         file.write(pointData)
   
while  True:
    # check for gps connected on Serial or USB
   if gps_con == 0 and os.path.exists('/dev/ttyS0') == True:
      ser = serial.Serial('/dev/ttyS0',9600,timeout = 10)
      gps_con = 1
      print "connected on Serial Tx/Rx"
   elif gps_con == 0 and os.path.exists('/dev/ttyUSB0') == True:
      ser = serial.Serial('/dev/ttyUSB0',9600,timeout = 10)
      gps_con = 1
      print "connected on USB0"
   elif gps_con == 0 and os.path.exists('/dev/ttyUSB1') == True:
      ser = serial.Serial('/dev/ttyUSB1',9600,timeout = 10)
      gps_con = 1
      print "connected on USB1"

   if gps_con == 1:
      gps = ser.readline()
      if gps[1 : 6] == "GNGLL" and len(gps) > 68 and (gps[3] == "N" or gps[3] == "S")and fix > 1:
         lat1 = int(gps[18:20]) + (Decimal(int(gps[21:27]))/(Decimal(60)))
         if gps1[28:29] == "S":
            lat1 = 0 - lat1
         lon1 = int(gps[30:33]) + (Decimal(int(gps[34:40]))/(Decimal(60)))
         if gps[41:42] == "W":
            lon1 = 0 - lon1
            pointData = "LAT:, " +str(lat1)
            
      if gps[1 : 6] == "GNGGA":
         gps = gps.split(',',14)
      if gps[1:6] == "GPGSA":
         fix = int(gps[9:10])
      if gps[1 : 6] == "GNGGA" and len(gps) > 68 and (gps[3] == "N" or gps[3] == "S")and fix > 1:
         lat = int(gps[18:20]) + (Decimal(int(gps[20:22]))/(Decimal(60))) + (Decimal(int(gps[23:27]))/(Decimal(360000)))
         if gps[28:29] == "S":
            lat = 0 - lat
         lon = int(gps[30:33]) + (Decimal(int(gps[33:35]))/(Decimal(60))) + (Decimal(int(gps[36:40]))/(Decimal(360000)))
         if gps[41:42] == "W":
            lon = 0 - lon
         if start < 4:
             A = lat
             B = lon
             pygame.draw.rect(windowSurfaceObj, redColor,Rect((width/1.5)- 4,(height/1.5) - 4,10,10),1)
             start += 1
         if start == 4:
            now = datetime.datetime.now()
            timestamp = now.strftime("%y/%m/%d-%H:%M:%S")
            timp = "TIME:, " + str(timestamp) + ", LAT:, " + str(lat) + ", LON:, " + str(lon) + ", SPEED:, " + str(speed) + ", ANGLE:, " + str(angle)  + "\n"
            with open("/run/shm/log.txt", "a") as file:
               file.write(timp)
            start +=1
         else:
             start += 1
             X = lat
             Y = lon
             pygame.draw.rect(windowSurfaceObj, redColor,Rect(((A-X)* J)+(width/2),((B-Y)*J)+ (height/2),3,3))
             pygame.display.update()
             time.sleep(.25)
             pygame.draw.rect(windowSurfaceObj, yellowColor,Rect(((A-X)* J)+(width/2),((B-Y)*J)+ (height/2),3,3))
             if oldX != 0:
                pygame.draw.line(windowSurfaceObj, yellowColor,  (((A-oldX)* J)+(width/2),((B-oldY)*J)+ (height/2)), (((A-X)* J)+(width/2),((B-Y)*J)+ (height/2)))
         msg = "LAT: " + str(lat) + " LON: " + str(lon) + "  SPEED: " + str(speed) + " ANGLE: " + str(angle) + " SCALE: " + str(((Decimal(1)/Decimal(J))*Decimal(10000)))[:4]  + " Km/Px"
         print_text(msg,greenColor,width,height)
         pygame.display.update()
         now = datetime.datetime.now()
         timestamp = now.strftime("%y/%m/%d-%H:%M:%S")
         timp = "TIME:, " + str(timestamp) + ", LAT:, " + str(lat) + ", LON:, " + str(lon) + ", SPEED:, " + str(speed) + ", ANGLE:, " + str(angle)  + "\n"
         with open("/run/shm/log.txt", "a") as file:
            file.write(timp)
         if start > 4:
            oldX = X
            oldY = Y
      if gps[1 : 6] == "GNRMC" and fix > 1:
         gps2 = gps.split(',',14)
         speed = gps2[7]
         angle = gps2[8]
         msg = "LAT: " + str(lat) + " LON: " + str(lon) + "  SPEED: " + str(speed) + " ANGLE: " + str(angle) + " SCALE: " + str(((Decimal(1)/Decimal(J))*Decimal(10000)))[:4] + " Km/Px"
         print_text(msg,greenColor,width,height)
         pygame.display.update()
      if fix <= 1:
         msg = "LAT: " + str(lat) + " LON: " + str(lon) + "  SPEED: " + str(speed) + " ANGLE: " + str(angle) + " SCALE: " + str(((Decimal(1)/Decimal(J))*Decimal(10000)))[:4]  + " Km/Px"
         print_text(msg,redColor,width,height)
         pygame.display.update()
         print gps

   # mouse and keyboard
   for event in pygame.event.get():
       if event.type == QUIT:
          pygame.quit()
          sys.exit()

       elif event.type == MOUSEBUTTONUP or event.type == KEYDOWN:
          z =  0
          kz = 0
          if event.type == KEYDOWN:
             kz = event.key
             # screen capture
             if kz == K_s:
                now = datetime.datetime.now()
                timestamp = now.strftime("%y%m%d%H%M%S")
                pygame.image.save(windowSurfaceObj, '/home/pi/scr' + str(timestamp) + '.bmp')

          if event.type == MOUSEBUTTONUP:
             mousex, mousey = event.pos
             # click bottom right to zoom in
             if mousex > width * 0.9 and mousey > height * 0.9:
                J = J * 2
                fileplot(J)
             # click bottom left to zoom out
             if mousex < width * 0.1 and mousey > height * 0.9:
                J = J / 2
                fileplot(J)
            # click top right to log point location
             if mousex > width * 0.9 and mousey < height * 0.1:
                plotpoint()

Any ideas on how best to approach this? is pygame the right answer or would this be easier in something else like Tkinter or QT?

Posted: **Tue Sep 12, 2017 3:13 pm**

Interesting project! Not much insight into your coding problems here, but make sure you know what you are getting with RTKlib. I read on it extensively and played with it some, however, I ended up putting together a dual frequency RTK system. Most RTKlib users use a single frequency which is usually only semi-stable. Not saying don't use it - but be very sure all of your quality checks are good at all times you are using it, not just at the beginning. Also be aware that vertical error is 2x the horizontal error if you are doing any drainage surveys (this is true with any GPS setup). I personally find that post processing is typically better for what I have done (ie - more flexible). Using something like OPUS (if you are in the US) for single points is usually more accurate than a base/rover setup, but not sure if they can use single frequency data.

Posted: **Thu Sep 28, 2017 6:53 pm**

Thanks for the feedback! I am aware of some of the error issues, and really looking for something to get me reasonable horizontal accuracy that I can do asbuilts of utility installs with around the farm. I "know" where the water line is, but when you start trying to dig and find it later on, being able to say "it's here" within a foot versus 3-6 feet is a big difference.
Still plugging away at it.

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