Python - 点列表的下采样，具有列表中两个相邻点之间的给定坐标和距离

Question

我真的希望有人可以帮助我！我试图让这个脚本按我的意愿运行，但我似乎无法掌握它。

要处理的数据文件是从 GPS 输入的，如下所示：

Line 20081002-1119.nmea
$GPGGA,094406.00,5849.40174,N,01738.15828,E,2,08,00.9,00003.26,M,0024.93,M,005,0734*62
$GPGGA,094407.00,5849.40177,N,01738.15827,E,2,08,00.9,00003.22,M,0024.93,M,005,0734*6B
$GPGGA,094408.00,5849.40174,N,01738.15826,E,2,08,00.9,00003.00,M,0024.93,M,006,0734*65
$GPGGA,094409.00,5849.40171,N,01738.15831,E,2,08,00.9,00003.24,M,0024.93,M,005,0734*62
$GPGGA,094410.00,5849.40176,N,01738.15833,E,2,08,00.9,00003.29,M,0024.93,M,006,0734*61
$GPGGA,094411.00,5849.40172,N,01738.15831,E,2,08,00.9,00003.31,M,0024.93,M,004,0734*6D
$GPGGA,094412.00,5849.40172,N,01738.15830,E,2,08,00.9,00003.15,M,0024.93,M,005,0734*68
$GPGGA,094413.00,5849.40175,N,01738.15834,E,2,08,00.9,00003.18,M,0024.93,M,005,0734*67
$GPGGA,094414.00,5849.40173,N,01738.15835,E,2,08,00.9,00003.16,M,0024.93,M,006,0734*6A
EOL

我的输出文件应该是这样的（现在加上距离只是为了显示我想要的）：

Line 20081002-1119.nmea
58.853952   17.643113   102.15 
58.853946   17.643243   101.63 
58.853939   17.643372   105.93 
58.853933   17.643503   104.01 
58.853927   17.643633   104.25 
...
EOL

这些列是：经度、纬度、到上面点的距离。

如何将其下采样到两点之间的给定间隔（在我的情况下为 100 米）？

到目前为止我管理的脚本：`

indata=open('C:/nav.nmea', 'r')
outdata=open('C:/nav_out.txt', 'w')

from math import *

coords_list=[]
coords=[]

def distance(coords_list):
    for (longi2,lati2) in coords_list:
        for (longi1,lati1) in coords_list:
            a = sin(lati1) * sin(lati2)+cos(longi1-longi2)*cos(lati1) * cos(lati2)
            c= 2* asin(sqrt(a))

            s= (6367* c)/100000 # For results in meters

        if s<100:
            # Here I want to discard current line if not s<100 and jump to the next line
        else:
            "Return the valid lines"
    return s


for line in indata:

    if line.startswith('$GPGGA'):

        data=line.split(",")
        # Import only coordinates from input file

        LON=float(data[2])/100

        LAT=float(data[4])/100

        # Convert coordinates from DDMM.MMMM to DD.DDDDDD

        lon=((LON-int(LON))/60)*100+int(LON)

        lat=((LAT-int(LAT))/60)*100+int(LAT)

        coords_list.append((lon,lat))

        outdata.writelines("%0.6f\t" %lon)

        outdata.writelines("%0.6f\t" %lat)
        outdata.writelines("%s \n" %distance(coords_list))


    elif line.startswith('EOL'):

        outdata.writelines("EOL")

    elif line.startswith('Line'):

        LineID=line

        outdata.writelines('\n%s' %LineID)


indata.close()     

outdata.close() 

`

Answer 1

对于曲线中的点减少，您可能想要使用Ramer–Douglas–Peucker algorithm。这保持了曲线的整体形状，但去除了细节，去除的量可以通过一个参数来控制。

请注意，链接的维基百科页面上的代码是伪代码，而不是 python。

---

我找到了一个python implementation of the DP line-simplication algorthim，我没有测试过，不能保证它的正确性。

Answer 2

这是一种相当简单的数据下采样方法：coord1 用于存储先前的坐标。每次通过循环，都会计算coord1 和新坐标coord2 之间的距离。当距离

import math
import itertools

def distance(coord1,coord2):
    longi1,lati1=coord1
    longi2,lati2=coord2
    a = (math.sin(lati1)*math.sin(lati2)
         +math.cos(longi1-longi2)*math.cos(lati1)*math.cos(lati2))
    c = 2*math.asin(math.sqrt(a))
    s = (6367*c)/100000 # For results in meters
    return s

with open('nav.nmea', 'r') as indata:
    with open('nav_out.txt', 'w') as outdata:
        coords=[]
        coord1=None
        for line in indata:
            if line.startswith('$GPGGA'):
                data=line.split(",")
                # Import only coordinates from input file
                LON=float(data[2])/100
                LAT=float(data[4])/100
                # Convert coordinates from DDMM.MMMM to DD.DDDDDD
                lon=((LON-int(LON))/60)*100+int(LON)
                lat=((LAT-int(LAT))/60)*100+int(LAT)
                coords.append((lon,lat))
                if coord1 is None:
                    # The first time through the loop `coord1` is None
                    outdata.write('%0.6f\t%0.6f\t%s \n'%(lon,lat,0))
                    coord1=(lon,lat)
                else:
                    coord2=(lon,lat)
                    dist=distance(coord1,coord2)
                    if dist<100:
                        # go back to the beginning of the loop
                        continue
                    outdata.write('%0.6f\t%0.6f\t%s \n'%(lon,lat,dist))
                    coord1=coord2
            elif line.startswith('EOL'):
                outdata.writelines("EOL")
            elif line.startswith('Line'):
                LineID=line
                outdata.writelines('\n%s' %LineID)