### Coordinate Transformation Examples in Rust

Source: https://github.com/athxx/coordtransform-rs/blob/main/README.md

Demonstrates various coordinate system conversions including BD09 to GCJ02, GCJ02 to BD09, WGS84 to GCJ02, GCJ02 to WGS84, BD09 to WGS84, WGS84 to BD09, WGS84 to EPSG:3857, EPSG:3857 to WGS84, GCJ02 to EPSG:3857, and BD09 to EPSG:3857.

```rust
use coordtransform::*

fn main() {
    // 百度坐标系 -> 火星坐标系
    let (lon, lat) = bd09_to_gcj02(116.404, 39.915);
    println!("BD09 to GCJ02: ({}, {})", lon, lat);

    // 火星坐标系 -> 百度坐标系
    let (lon, lat) = gcj02_to_bd09(116.404, 39.915);
    println!("GCJ02 to BD09: ({}, {})", lon, lat);

    // WGS84坐标系 -> 火星坐标系
    let (lon, lat) = wgs84_to_gcj02(116.404, 39.915);
    println!("WGS84 to GCJ02: ({}, {})", lon, lat);

    // 火星坐标系 -> WGS84坐标系 gcj02 -> WGS84
    let (lon, lat) = gcj02_to_wgs84(116.404, 39.915);
    println!("GCJ02 to WGS84: ({}, {})", lon, lat);

    // 百度坐标系 -> WGS84坐标系
    let (lon, lat) = bd09_to_wgs84(116.404, 39.915);
    println!("BD09 to WGS84: ({}, {})", lon, lat);

    // WGS84坐标系 -> 百度坐标系
    let (lon, lat) = wgs84_to_bd09(116.404, 39.915);
    println!("WGS84 to BD09: ({}, {})", lon, lat);

    // WGS84坐标系 -> EPSG:3857坐标系 (Web墨卡托投影)
    let (x, y) = wgs84_to_epsg3857(116.404, 39.915);
    println!("WGS84 to EPSG:3857: ({}, {})", x, y);

    // EPSG:3857坐标系 -> WGS84坐标系
    let (lon, lat) = epsg3857_to_wgs84(12958752.0, 4825923.0);
    println!("EPSG:3857 to WGS84: ({}, {})", lon, lat);

    // GCJ02坐标系 -> EPSG:3857坐标系
    let (x, y) = gcj02_to_epsg3857(116.404, 39.915);
    println!("GCJ02 to EPSG:3857: ({}, {})", x, y);

    // BD09坐标系 -> EPSG:3857坐标系
    let (x, y) = bd09_to_epsg3857(116.404, 39.915);
    println!("BD09 to EPSG:3857: ({}, {})", x, y);
}
```

--------------------------------

### Complete Coordinate Conversion Workflow

Source: https://context7.com/athxx/coordtransform-rs/llms.txt

Use this example to demonstrate a full coordinate conversion workflow, including conversion to Amap/Google China (GCJ02), Baidu Maps (BD09), and Web Tiles (EPSG:3857). It also shows a precision test for round-trip conversion from EPSG:3857 back to WGS84. Ensure the 'coordtransform' crate is added as a dependency.

```rust
use coordtransform::*

fn main() {
    // Scenario: You receive GPS coordinates from a device and need to display
    // them on multiple Chinese map services

    let gps_lon = 116.404;  // Raw GPS longitude (WGS84)
    let gps_lat = 39.915;   // Raw GPS latitude (WGS84)

    println!("=== Multi-Platform Coordinate Conversion ===\n");
    println!("Original GPS (WGS84): ({}, {})\n", gps_lon, gps_lat);

    // For Google Maps China / Amap (GCJ02)
    let (amap_lon, amap_lat) = wgs84_to_gcj02(gps_lon, gps_lat);
    println!("For Amap/Google China (GCJ02): ({:.6}, {:.6})", amap_lon, amap_lat);

    // For Baidu Maps (BD09)
    let (baidu_lon, baidu_lat) = wgs84_to_bd09(gps_lon, gps_lat);
    println!("For Baidu Maps (BD09): ({:.6}, {:.6})", baidu_lon, baidu_lat);

    // For Web tiles / OpenStreetMap (EPSG:3857)
    let (web_x, web_y) = wgs84_to_epsg3857(gps_lon, gps_lat);
    println!("For Web Tiles (EPSG:3857): ({:.2}, {:.2})\n", web_x, web_y);

    // Round-trip precision test
    println!("=== Precision Test (Round-Trip) ===\n");
    let (back_lon, back_lat) = epsg3857_to_wgs84(web_x, web_y);
    println!("Original: ({:.10}, {:.10})", gps_lon, gps_lat);
    println!("After round-trip: ({:.10}, {:.10})", back_lon, back_lat);
    println!("Difference: ({:.2e}, {:.2e})",
             (back_lon - gps_lon).abs(),
             (back_lat - gps_lat).abs());
}
```

--------------------------------

### Run Benchmark Tests

Source: https://github.com/athxx/coordtransform-rs/blob/main/README.md

Execute the benchmark tests for the coordinate transformation library using Cargo.

```bash
cargo bench
```

--------------------------------

### Run Tests

Source: https://github.com/athxx/coordtransform-rs/blob/main/README.md

Execute the unit tests for the coordinate transformation library using Cargo.

```bash
cargo test
```

--------------------------------

### Add coordtransform to Cargo.toml

Source: https://github.com/athxx/coordtransform-rs/blob/main/README.md

To use the library, add the `coordtransform` crate to your project's `Cargo.toml` file.

```toml
[dependencies]
coordtransform = "0.3.0"
```

--------------------------------

### Convert EPSG:3857 to BD09

Source: https://context7.com/athxx/coordtransform-rs/llms.txt

Converts Web Mercator projection coordinates to BD09 Baidu coordinates.

```rust
use coordtransform::epsg3857_to_bd09;

fn main() {
    // Web Mercator coordinates
    let x = 12958752.67;
    let y = 4825923.04;

    // Convert to BD09 for display on Baidu Maps
    let (lon, lat) = epsg3857_to_bd09(x, y);

    println!("EPSG:3857: ({}, {})", x, y);
    println!("BD09: ({:.6}, {:.6})", lon, lat);
}
```

--------------------------------

### Convert BD09 to EPSG:3857

Source: https://context7.com/athxx/coordtransform-rs/llms.txt

Converts BD09 Baidu coordinates to Web Mercator projection.

```rust
use coordtransform::bd09_to_epsg3857;

fn main() {
    // BD09 coordinates (from Baidu Maps)
    let bd09_lon = 116.404;
    let bd09_lat = 39.915;

    // Convert to Web Mercator
    let (x, y) = bd09_to_epsg3857(bd09_lon, bd09_lat);

    println!("BD09: ({}, {})", bd09_lon, bd09_lat);
    println!("EPSG:3857: ({:.2}, {:.2})", x, y);
    // Output:
    // BD09: (116.404, 39.915)
    // EPSG:3857: (12956641.65, 4851095.83)
}
```

--------------------------------

### Convert EPSG:3857 to WGS84

Source: https://context7.com/athxx/coordtransform-rs/llms.txt

Converts Web Mercator projection coordinates back to WGS84 geographic coordinates.

```rust
use coordtransform::epsg3857_to_wgs84;

fn main() {
    // Web Mercator coordinates in meters
    let x = 12958034.01;
    let y = 4853597.99;

    // Convert to geographic coordinates
    let (lon, lat) = epsg3857_to_wgs84(x, y);

    println!("EPSG:3857: ({}, {})", x, y);
    println!("WGS84: ({:.6}, {:.6})", lon, lat);
    // Output:
    // EPSG:3857: (12958034.01, 4853597.99)
    // WGS84: (116.404000, 39.915000)
}
```

--------------------------------

### Convert EPSG:3857 to GCJ02

Source: https://context7.com/athxx/coordtransform-rs/llms.txt

Converts Web Mercator projection coordinates to GCJ02 Mars coordinates.

```rust
use coordtransform::epsg3857_to_gcj02;

fn main() {
    // Web Mercator coordinates
    let x = 12958752.67;
    let y = 4825923.04;

    // Convert to GCJ02 for display on Amap
    let (lon, lat) = epsg3857_to_gcj02(x, y);

    println!("EPSG:3857: ({}, {})", x, y);
    println!("GCJ02: ({:.6}, {:.6})", lon, lat);
}
```

--------------------------------

### Convert Mars Coordinates (GCJ02) to Baidu Coordinates (BD09)

Source: https://context7.com/athxx/coordtransform-rs/llms.txt

Use this function to convert coordinates from the Mars system to Baidu's system, useful for displaying Google Maps or Amap data on Baidu Maps.

```rust
use coordtransform::gcj02_to_bd09;

fn main() {
    // Coordinates in GCJ02 (Google Maps China / Amap)
    let gcj02_lon = 116.404;
    let gcj02_lat = 39.915;

    // Convert to BD09 (Baidu)
    let (bd09_lon, bd09_lat) = gcj02_to_bd09(gcj02_lon, gcj02_lat);

    println!("GCJ02: ({}, {})", gcj02_lon, gcj02_lat);
    println!("BD09: ({:.10}, {:.10})", bd09_lon, bd09_lat);
    // Output:
    // GCJ02: (116.404, 39.915)
    // BD09: (116.4103694937, 39.9213369935)
}
```

--------------------------------

### Convert WGS84 to EPSG:3857

Source: https://context7.com/athxx/coordtransform-rs/llms.txt

Converts WGS84 geographic coordinates to Web Mercator projection coordinates used in web mapping.

```rust
use coordtransform::wgs84_to_epsg3857;

fn main() {
    // Geographic coordinates in degrees
    let wgs84_lon = 116.404;  // Beijing longitude
    let wgs84_lat = 39.915;   // Beijing latitude

    // Convert to Web Mercator (meters)
    let (x, y) = wgs84_to_epsg3857(wgs84_lon, wgs84_lat);

    println!("WGS84: ({}, {})", wgs84_lon, wgs84_lat);
    println!("EPSG:3857: ({:.2}, {:.2})", x, y);
    // Output:
    // WGS84: (116.404, 39.915)
    // EPSG:3857: (12958034.01, 4853597.99)

    // Test with multiple cities
    let cities = [
        ("Shanghai", 121.4737, 31.2304),
        ("New York", -74.0060, 40.7128),
        ("London", 0.1276, 51.5074),
    ];

    for (city, lon, lat) in cities {
        let (x, y) = wgs84_to_epsg3857(lon, lat);
        println!("{}: ({:.2}, {:.2})", city, x, y);
    }
}
```

--------------------------------

### Convert GCJ02 to EPSG:3857

Source: https://context7.com/athxx/coordtransform-rs/llms.txt

Converts GCJ02 Mars coordinates to Web Mercator projection by first converting to WGS84.

```rust
use coordtransform::gcj02_to_epsg3857;

fn main() {
    // GCJ02 coordinates (from Amap)
    let gcj02_lon = 116.404;
    let gcj02_lat = 39.915;

    // Convert to Web Mercator for tile calculations
    let (x, y) = gcj02_to_epsg3857(gcj02_lon, gcj02_lat);

    println!("GCJ02: ({}, {})", gcj02_lon, gcj02_lat);
    println!("EPSG:3857: ({:.2}, {:.2})", x, y);
    // Output:
    // GCJ02: (116.404, 39.915)
    // EPSG:3857: (12957352.67, 4852064.57)
}
```

--------------------------------

### Convert Baidu Coordinates (BD09) to Mars Coordinates (GCJ02)

Source: https://context7.com/athxx/coordtransform-rs/llms.txt

Use this function to convert coordinates from Baidu's system to the Mars system, useful for displaying Baidu data on Google Maps China or Amap.

```rust
use coordtransform::bd09_to_gcj02;

fn main() {
    // Beijing coordinates in BD09 (Baidu)
    let bd09_lon = 116.404;
    let bd09_lat = 39.915;

    // Convert to GCJ02 (Mars coordinates)
    let (gcj02_lon, gcj02_lat) = bd09_to_gcj02(bd09_lon, bd09_lat);

    println!("BD09: ({}, {})", bd09_lon, bd09_lat);
    println!("GCJ02: ({:.10}, {:.10})", gcj02_lon, gcj02_lat);
    // Output:
    // BD09: (116.404, 39.915)
    // GCJ02: (116.3976272912, 39.9086567396)
}
```

--------------------------------

### bd09_to_gcj02

Source: https://context7.com/athxx/coordtransform-rs/llms.txt

Converts coordinates from Baidu Coordinate System (BD09) to Mars Coordinate System (GCJ02).

```APIDOC
## FUNCTION bd09_to_gcj02

### Description
Converts coordinates from Baidu Coordinate System (BD09) to Mars Coordinate System (GCJ02).

### Parameters
- **bd09_lon** (f64) - Required - Longitude in BD09 format
- **bd09_lat** (f64) - Required - Latitude in BD09 format

### Response
- **(f64, f64)** - Returns a tuple containing the converted (longitude, latitude) in GCJ02 format.
```

--------------------------------

### gcj02_to_bd09

Source: https://context7.com/athxx/coordtransform-rs/llms.txt

Converts coordinates from Mars Coordinate System (GCJ02) to Baidu Coordinate System (BD09).

```APIDOC
## FUNCTION gcj02_to_bd09

### Description
Converts coordinates from Mars Coordinate System (GCJ02) to Baidu Coordinate System (BD09).

### Parameters
- **gcj02_lon** (f64) - Required - Longitude in GCJ02 format
- **gcj02_lat** (f64) - Required - Latitude in GCJ02 format

### Response
- **(f64, f64)** - Returns a tuple containing the converted (longitude, latitude) in BD09 format.
```

--------------------------------

### Convert WGS84 to BD09

Source: https://context7.com/athxx/coordtransform-rs/llms.txt

Performs a compound conversion from WGS84 GPS coordinates to Baidu BD09 coordinates.

```rust
use coordtransform::wgs84_to_bd09;

fn main() {
    // Raw GPS coordinates (WGS84)
    let wgs84_lon = 116.404;
    let wgs84_lat = 39.915;

    // Convert directly to BD09 for Baidu Maps
    let (bd09_lon, bd09_lat) = wgs84_to_bd09(wgs84_lon, wgs84_lat);

    println!("WGS84 (GPS): ({}, {})", wgs84_lon, wgs84_lat);
    println!("BD09 (Baidu): ({:.10}, {:.10})", bd09_lon, bd09_lat);
    // Output:
    // WGS84 (GPS): (116.404, 39.915)
    // BD09 (Baidu): (116.4166272438, 39.9226995522)
}
```

--------------------------------

### Convert Baidu Coordinates (BD09) to WGS84 Coordinates

Source: https://context7.com/athxx/coordtransform-rs/llms.txt

Converts Baidu coordinates (BD09) directly to standard GPS coordinates (WGS84). This is a compound conversion that first converts BD09 to GCJ02, then GCJ02 to WGS84.

```rust
use coordtransform::bd09_to_wgs84;

fn main() {
    // Coordinates from Baidu Maps (BD09)
    let bd09_lon = 116.404;
    let bd09_lat = 39.915;

    // Convert directly to WGS84 (standard GPS)
    let (wgs84_lon, wgs84_lat) = bd09_to_wgs84(bd09_lon, bd09_lat);

    println!("BD09 (Baidu): ({}, {})", bd09_lon, bd09_lat);
    println!("WGS84 (GPS): ({:.10}, {:.10})", wgs84_lon, wgs84_lat);
    // Output:
    // BD09 (Baidu): (116.404, 39.915)
    // WGS84 (GPS): (116.3913836995, 39.9072532145)
}
```

--------------------------------

### bd09_to_wgs84

Source: https://context7.com/athxx/coordtransform-rs/llms.txt

Converts Baidu coordinates (BD09) directly to standard GPS coordinates (WGS84).

```APIDOC
## FUNCTION bd09_to_wgs84

### Description
Converts Baidu coordinates (BD09) directly to standard GPS coordinates (WGS84) via a compound conversion.

### Parameters
- **bd09_lon** (f64) - Required - Longitude in BD09 format
- **bd09_lat** (f64) - Required - Latitude in BD09 format

### Response
- **(f64, f64)** - Returns a tuple containing the converted (longitude, latitude) in WGS84 format.
```

--------------------------------

### Convert Mars Coordinates (GCJ02) to WGS84 Coordinates

Source: https://context7.com/athxx/coordtransform-rs/llms.txt

Converts coordinates from the Mars Coordinate System (GCJ02) back to standard GPS coordinates (WGS84). This is useful for storing coordinates in a standard format or for use with international mapping services.

```rust
use coordtransform::gcj02_to_wgs84;

fn main() {
    // Coordinates from Amap (GCJ02)
    let gcj02_lon = 116.404;
    let gcj02_lat = 39.915;

    // Convert to WGS84 (standard GPS)
    let (wgs84_lon, wgs84_lat) = gcj02_to_wgs84(gcj02_lon, gcj02_lat);

    println!("GCJ02: ({}, {})", gcj02_lon, gcj02_lat);
    println!("WGS84: ({:.10}, {:.10})", wgs84_lon, wgs84_lat);
    // Output:
    // GCJ02: (116.404, 39.915)
    // WGS84: (116.3977555008, 39.9135957185)
}
```

--------------------------------

### Convert WGS84 Coordinates to Mars Coordinates (GCJ02)

Source: https://context7.com/athxx/coordtransform-rs/llms.txt

Converts standard GPS coordinates (WGS84) to the Mars Coordinate System (GCJ02). This is essential for displaying raw GPS data on Chinese mapping services like Google Maps China or Amap. Coordinates outside China remain unchanged.

```rust
use coordtransform::wgs84_to_gcj02;

fn main() {
    // Raw GPS coordinates (WGS84)
    let wgs84_lon = 116.404;
    let wgs84_lat = 39.915;

    // Convert to GCJ02 for display on Amap
    let (gcj02_lon, gcj02_lat) = wgs84_to_gcj02(wgs84_lon, wgs84_lat);

    println!("WGS84 (GPS): ({}, {})", wgs84_lon, wgs84_lat);
    println!("GCJ02 (Amap): ({:.10}, {:.10})", gcj02_lon, gcj02_lat);
    // Output:
    // WGS84 (GPS): (116.404, 39.915)
    // GCJ02 (Amap): (116.4102444992, 39.9164042815)

    // Coordinates outside China remain unchanged
    let (lon, lat) = wgs84_to_gcj02(0.0, 0.0);
    println!("Outside China: ({}, {})", lon, lat);
    // Output: Outside China: (0, 0)
}
```

--------------------------------

### wgs84_to_gcj02

Source: https://context7.com/athxx/coordtransform-rs/llms.txt

Converts GPS coordinates (WGS84) to Mars Coordinate System (GCJ02).

```APIDOC
## FUNCTION wgs84_to_gcj02

### Description
Converts GPS coordinates (WGS84) to Mars Coordinate System (GCJ02). Coordinates outside China remain unchanged.

### Parameters
- **wgs84_lon** (f64) - Required - Longitude in WGS84 format
- **wgs84_lat** (f64) - Required - Latitude in WGS84 format

### Response
- **(f64, f64)** - Returns a tuple containing the converted (longitude, latitude) in GCJ02 format.
```

--------------------------------

### gcj02_to_wgs84

Source: https://context7.com/athxx/coordtransform-rs/llms.txt

Converts Mars Coordinate System (GCJ02) back to standard GPS coordinates (WGS84).

```APIDOC
## FUNCTION gcj02_to_wgs84

### Description
Converts Mars Coordinate System (GCJ02) back to standard GPS coordinates (WGS84).

### Parameters
- **gcj02_lon** (f64) - Required - Longitude in GCJ02 format
- **gcj02_lat** (f64) - Required - Latitude in GCJ02 format

### Response
- **(f64, f64)** - Returns a tuple containing the converted (longitude, latitude) in WGS84 format.
```

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