Navit学习笔记（三）
通过Navit学习笔记（一）、Navit学习笔记（二）的介绍，我们已经对Navit有了初步的认识。Navit是学习导航程序开发很好的例子，从本文开始，我们对Navit的源代码做简要的分析，以求学习和提高。
navit的内核包括：
1、一个设置地图对象
2、一个或多个车辆
3、一套用于地图解析的图像对象
4、一个用于显示的GUI对象
5、一个路经对象
6、一个导航对象
...
在详细介绍Navit内核前，我们先来学习Navit的坐标模块，坐标模块包括projection投影模块，coor坐标模块。在projection投影模块中有文件projection.h 和 projection.c ，在projection.h中定义了：
枚举对象：
1、projection：主要定义投影的类型定义
*projection_none 不投影,
*projection_mg mg上投影,
*projection_garmin garmin投影,
*projection_screen 屏幕投影,
*projection_utm utm投影,
*projection_gk gk投影
2、enum map_datum 定义了数据的投影坐标系包括none、wgs84标准和dhdn标准
*map_datum_none none，
*map_datum_wgs84 wgs84标准,
*map_datum_dhdn dhdn标准
3、定义了coord结构，改结构使用coord.h中的定义
4、根据枚举projection定义了 enum projection projection_from_name(const char *name,struct coord *offset)函数用于将字符型的投影类型名称转换成字符projection投影枚举类型。
5、定义函数char *projection_to_name(enum projection proj,struct coord *offset)用于将投影类型转换成字符形式。
整个porjection的实现代码如下：
2 #include <glib.h>
3 #include "coord.h"
4 #include "debug.h"
5
6 #include "projection.h" //头文件引用
7
8 //定义投影类型名称结构
9 struct projection_name {
10 enum projection projection; //枚举 projection 类型
11 char *name; //投影名称
12 };
13
14 //根据projection_name结构定义 projection_names[]数组，数组中projection枚举类型和char类型名称一一对应
15 struct projection_name projection_names[]={
16 {projection_none, ""},
17 {projection_mg, "mg"},
18 {projection_garmin, "garmin"},
19 {projection_utm, "utm"},
20 {projection_gk, "gk"},
21 };
22
23 //实现头文件中的projection_from_name函数，其中参数name为projection类型名词，offset为coord结构
24 enum projection
25 projection_from_name(const char *name, struct coord *offset)
26 {
27 int i;
28 int zone;
29 char ns;
30
31 for (i=0 ; i < sizeof(projection_names)/sizeof(struct projection_name) ; i++)
32 {
33 if (! strcmp(projection_names[i].name, name))
34 return projection_names[i].projection;
35 }
36 if (offset) {
37 if (sscanf(name,"utm%d%c",&zone,&ns) == 2 && zone > 0 && zone <= 60 && (ns == 'n' || ns == 's')) {
38 offset->x=zone*1000000;
39 offset->y=(ns == 's' ? -10000000:0);
40 return projection_utm;
41 }
42 }
43 return projection_none;
44 }
45 //返回projection类型的名称
46 char *
47 projection_to_name(enum projection proj, struct coord *offset)
48 {
49 int i;
50
51 for (i=0 ; i < sizeof(projection_names)/sizeof(struct projection_name) ; i++) {
52 if (projection_names[i].projection == proj)
53 return projection_names[i].name;
54 }
55 return NULL;
56 }
在coord.h文件中定义了
1、宏定义
*coord_is_equal(a,b)用于对两个coord结构的相等操作
*为了防止一些平台出现浮点截断误差，定义了
2 /**
3 * On platforms where we are trying to avoid floats, sometimes we can't.
4 * It is better on these platforms to use single precision floating points
5 * over double percision ones since performance is much better.
6 */
7 typedef float navit_float;
8 #define navit_sin(x) sinf(x)
9 #define navit_cos(x) cosf(x)
10 #define navit_tan(x) tanf(x)
11 #define navit_atan(x) atanf(x)
12 #define navit_acos(x) acosf(x)
13 #define navit_asin(x) asinf(x)
14 #define navit_sqrt(x) sqrtf(x)
15 #else
16 typedef double navit_float;
17 #define navit_sin(x) sin(x)
18 #define navit_cos(x) cos(x)
19 #define navit_tan(x) tan(x)
20 #define navit_atan(x) atan(x)
21 #define navit_acos(x) acos(x)
22 #define navit_asin(x) asin(x)
23 #define navit_sqrt(x) sqrt(x)
24 #endif
2、结构类型
*coord 定义了int类型的墨卡托坐标系
int x; /*!< X-Value */
int y; /*!< Y-Value */
};
* pcoord 定义了一个包含projection枚举类型的墨卡托坐标系
enum projection pro;
int x; /*!< X-Value */
int y; /*!< Y-Value */
};
*coord_rect 定义了矩形形状的坐标系结构
struct coord lu; //矩形左上点的coord结构
struct coord rl; //矩形有下点的coord结构
};
*coord_d 双精度的墨卡托坐标系
double x; /*!< X-Value */
double y; /*!< Y-Value */
};
*coord_geo_cart WGS84标准的笛卡尔坐标系
navit_float x; /*!< X-Value */
navit_float y; /*!< Y-Value */
navit_float z; /*!< Z-Value */
};
*struct attr;
3、枚举类型
*coord_format 答应地理坐标的格式化类型枚举
{ /**
* Degrees with decimal places.Ie 20.5000 N 110.5000 E*/
DEGREES_DECIMAL,
/**
* Degrees and minutes.ie 20 30.00 N 110 30.00 E*/
DEGREES_MINUTES,
/**
* Degrees, minutes and seconds.ie 20 30 30.00 N 110 30 30 E*/
DEGREES_MINUTES_SECONDS
};
4、函数
2 struct coord * coord_get(unsigned char **p);
3 //获取新的墨卡托坐标点
4 struct coord * coord_new(int x, int y);
5 //从attr结构多项中获取坐标系/点
6 struct coord * coord_new_from_attrs(struct attr *parent, struct attr **attrs);
7 //销毁墨卡托坐标系/点
8 void coord_destroy(struct coord *c);
9 //墨卡托坐标系/点分析
10 int coord_parse(const char *c_str, enum projection pro, struct coord *c_ret);
11 //包含
12 int pcoord_parse(const char *c_str, enum projection pro, struct pcoord *c_ret);
13 //坐标打印
14 void coord_print(enum projection pro, struct coord *c, FILE *out);
15 //新的矩形坐标范围框
16 struct coord_rect * coord_rect_new(struct coord *lu, struct coord *rl);
17
18 void coord_rect_destroy(struct coord_rect *r);
19 //区域重叠
20 int coord_rect_overlap(struct coord_rect *r1, struct coord_rect *r2);
21 //区域包含
22 int coord_rect_contains(struct coord_rect *r, struct coord *c);
23 //区域扩展
24 void coord_rect_extend(struct coord_rect *r, struct coord *c);
25 //坐标格式化
26 void coord_format(float lat,float lng, enum coord_format, char * buffer, int size);
5、coord.h定义的属性、函数
2 enum projection;
3 struct attr;
4 struct coord;
5 struct coord_rect;
6 struct pcoord;
7 struct coord *coord_get(unsigned char **p);
8 struct coord *coord_new(int x, int y);
9 struct coord *coord_new_from_attrs(struct attr *parent, struct attr **attrs);
10 void coord_destroy(struct coord *c);
11 struct coord_rect *coord_rect_new(struct coord *lu, struct coord *rl);
12 void coord_rect_destroy(struct coord_rect *r);
13 int coord_rect_overlap(struct coord_rect *r1, struct coord_rect *r2);
14 int coord_rect_contains(struct coord_rect *r, struct coord *c);
15 void coord_rect_extend(struct coord_rect *r, struct coord *c);
16 int coord_parse(const char *c_str, enum projection pro, struct coord *c_ret);
17 int pcoord_parse(const char *c_str, enum projection pro, struct pcoord *pc_ret);
18 void coord_print(enum projection pro, struct coord *c, FILE *out);
19 void coord_format(float lat, float lng, enum coord_format fmt, char *buffer, int size);
20 unsigned int coord_hash(const void *key);
21 int coord_equal(const void *a, const void *b);
