rt_raster_calc_gt_coeff()

int rt_raster_calc_gt_coeff	(	double	i_mag,
		double	j_mag,
		double	theta_i,
		double	theta_ij,
		double *	xscale,
		double *	xskew,
		double *	yskew,
		double *	yscale
	)

Calculates the coefficients of a geotransform given the physically significant parameters describing the transform.

Will fail if any of the result pointers is NULL, or if theta_ij has an illegal value (0 or PI).

Parameters

i_mag	size of a pixel along the transformed i axis
j_mag	size of a pixel along the transformed j axis
theta_i	angle by which the raster is rotated (radians positive clockwise)
theta_ij	angle from transformed i axis to transformed j axis (radians positive counterclockwise)
xscale	geotransform coefficient o_11
xskew	geotransform coefficient o_12
yskew	geotransform coefficient o_21
yscale	geotransform coefficient o_22

Returns

1 if the calculation succeeded, 0 if error.

Definition at line 318 of file rt_raster.c.

{
    double f ;        /* reflection flag 1.0 or -1.0 */
    double k_i ;      /* shearing coefficient */
    double s_i, s_j ; /* scaling coefficients */
    double cos_theta_i, sin_theta_i ;
 
    if ( (xscale==NULL) || (xskew==NULL) || (yskew==NULL) || (yscale==NULL)) {
        return 0;
    }
 
    if ( (theta_ij == 0.0) || (theta_ij == M_PI)) {
        return 0;
    }
 
    /* Reflection across the i axis */
    f=1.0 ;
    if (theta_ij < 0) {
        f = -1.0;
    }
 
    /* scaling along i axis */
    s_i = i_mag ;
 
    /* shearing parallel to i axis */
    k_i = tan(f*M_PI_2 - theta_ij) ;
 
    /* scaling along j axis */
    s_j = j_mag / (sqrt(k_i*k_i + 1)) ;
 
    /* putting it altogether */
    cos_theta_i = cos(theta_i) ;
    sin_theta_i = sin(theta_i) ;
    *xscale = s_i * cos_theta_i ;
    *xskew  = k_i * s_j * f * cos_theta_i + s_j * f * sin_theta_i ;
    *yskew  = -s_i * sin_theta_i ;
    *yscale = -k_i * s_j * f * sin_theta_i + s_j * f * cos_theta_i ;
    return 1;
}

Referenced by rt_raster_set_phys_params().

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