如何实现gpsd客户端(在C语言中)以获取纬度，经度和海拔? [英] How can I implement a gpsd client (in C) to get Latitude, Longitude and Altitude?

问题描述

我正在为启用GPS的Raspberry Pi编写一个数字处理数据记录C程序.我抓到了 gpsd ，它的示例应用程序cgps可以正确显示gps信息.我想使用 libgps 与守护程序交互，以便在应用程序中获取所有方便的信息，但其API的复杂性让我很快不知所措.

I am writing a number-crunching data-logging C program for my GPS enabled Raspberry Pi. I grabbed gpsd, and its sample app cgps displays gps information correctly. I wanted to use libgps to interface with the daemon so that I could have all that handy information in my app, but I was quickly overwhelmed by the complexity of its API.

HOWTO页面上的文档指向我看 libgps 页面上的C代码示例是如此简单，以至于无法使用.

The documentation on its HOWTO page points me to look at cgps and gpxlogger for example code, but there's so much coupling that I can't wade through it all. On the opposite end of the spectrum, the C code example on the libgps page is so stripped back that it's unusable.

有人能指出一个可能使这个说法神秘化的单一课堂样本吗?也许包含 getCoordinates()函数的东西?

Can anybody point me to a single class sample that might demystify this? Perhaps something that contains a getCoordinates() function?

推荐答案

我讲得太早了.浏览了其他SO问题之后，我遇到了这完全不相关的问题问题.这是我的略作修改的版本:

I spoke too soon. After browsing other SO questions, I ran into this completely unrelated question. Here's my very slightly modified version:

#include <gps.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <math.h>
#include <errno.h>

int main() {
struct timeval tv;
struct gps_data_t gps_data;

if ((gps_open("localhost", "2947", &gps_data)) == -1) {
    printf("code: %d, reason: %s\n", errno, gps_errstr(errno));
    return EXIT_FAILURE;
}
gps_stream(&gps_data, WATCH_ENABLE | WATCH_JSON, NULL);

while (1) {
    /* wait for 2 seconds to receive data */
    if (gps_waiting (&gps_data, 2000000)) {
        /* read data */
        if ((gps_read(&gps_data,NULL,0)) == -1) {
            printf("error occured reading gps data. code: %d, reason: %s\n", errno, gps_errstr(errno));
        } else {
            /* Display data from the GPS receiver. */
            if ((gps_data.status == STATUS_FIX) && 
                (gps_data.fix.mode == MODE_2D || gps_data.fix.mode == MODE_3D) &&
                !isnan(gps_data.fix.latitude) && 
                !isnan(gps_data.fix.longitude)) {
                    //gettimeofday(&tv, NULL); EDIT: tv.tv_sec isn't actually the timestamp!
                    printf("latitude: %f, longitude: %f, speed: %f, timestamp: %lf\n", gps_data.fix.latitude, gps_data.fix.longitude, gps_data.fix.speed, gps_data.fix.time); //EDIT: Replaced tv.tv_sec with gps_data.fix.time
            } else {
                printf("no GPS data available\n");
            }
        }
    }

    sleep(3);
}

/* When you are done... */
gps_stream(&gps_data, WATCH_DISABLE, NULL);
gps_close (&gps_data);

return EXIT_SUCCESS;
}

我通过运行 gcc -o gps filename.c -lm -lgps

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