[gdal-dev] angle of crossing two lines

[Martin Chapman]

Ahmet,

 

The following function will return the angle in decimal degrees given 3 points on a flat plane.  The three points create the angle.  If you have two intersecting lines then the angle of any given corner is the center point where the lines intersect and two end points of the lines that complete an angle.

 

// NOTE: the points must be fed to the function in clockwise order.  

// NOTE: the angle returned is an azimuth angle and not a trigonometric angle.  Azimuth angles start with zero at north and increase clockwise whereas trigonometric angles zero starts to the right (east) on the x axis and increase going counter clockwise.

 

const double PI = 3.1415926535897932384626433;

const double RAD2DEG = 180.0 / PI;

 

double GetAngle(const double& x1, const double& y1, const double& x2, const double& y2, const double& x3, const double& y3)

{

       double theta1 = atan2(y2 - y1, x2 - x1);

       double theta2 = atan2(y2 - y3, x2 - x3);

       double theta = (theta2 - theta1) * RAD2DEG;

       if (theta < 0) theta += 360.0;

       return theta;

}

 

// To get the intersection of two lines use:

// NOTE: returns FALSE if the lines don’t intersect

 

struct Point

{

       double x;

       double y;

};

 

struct Line

{

       Point point1;

       Point point2;

};

 

BOOL GetLineIntersection(const Line& line1, const Line& line2, double& x, double& y)

{

    double a1 = line1.point2.y - line1.point1.y;

    double b1 = line1.point1.x - line1.point2.x;

    double c1 = a1 * line1.point1.x + b1 * line1.point1.y;

    double a2 = line2.point2.y - line2.point1.y;

    double b2 = line2.point1.x - line2.point2.x;

    double c2 = a2 * line2.point1.x + b2 * line2.point1.y;

    double determinant = a1 * b2 - a2 * b1;

    if (determinant == 0) return FALSE;

 

    x = (b2 * c1 - b1 * c2) / determinant;

    y = (a1 * c2 - a2 * c1) / determinant;

 

       return TRUE;

}

 

Best regards,

Martin Chapman

 

From: gdal-dev [mailto:gdal-dev-bounces at lists.osgeo.org] On Behalf Of Ahmet Temiz
Sent: Monday, November 11, 2019 7:07 AM
To: gdal-dev
Subject: [gdal-dev] angle of crossing two lines

 

Hi,

I need to know angle of crossing two lines.

which function can I use?

 

regards

 

-- 

Ahmet Temiz
Jeoloji Müh.
Afet ve Acil Durum Yönetimi Başkanlığı
Bilgi İşlem  Dairesi Başkanlığı-CBS Grubu


________________________

Ahmet Temiz
Geological Eng.
Information Systems - GIS Group
Disaster and Emergency Management
of Presidency

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/gdal-dev/attachments/20191111/9866fd39/attachment.html>