rt_raster_calc_phys_params()

void rt_raster_calc_phys_params	(	double	xscale,
		double	xskew,
		double	yskew,
		double	yscale,
		double *	i_mag,
		double *	j_mag,
		double *	theta_i,
		double *	theta_ij
	)

Calculates the physically significant descriptors embodied in an arbitrary geotransform.

Always succeeds unless one or more of the output pointers is set to NULL.

Parameters

xscale	geotransform coefficient o_11
xskew	geotransform coefficient o_12
yskew	geotransform coefficient o_21
yscale	geotransform coefficient o_22
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)

Definition at line 250 of file rt_raster.c.

References return().

Referenced by RASTER_getGeotransform(), and rt_raster_get_phys_params().

{
    double theta_test ;

    if ( (i_mag==NULL) || (j_mag==NULL) || (theta_i==NULL) || (theta_ij==NULL))
        return ;

    /* pixel size in the i direction */
    *i_mag = sqrt(xscale*xscale + yskew*yskew) ;

    /* pixel size in the j direction */
    *j_mag = sqrt(xskew*xskew + yscale*yscale) ;

    /* Rotation
     * ========
     * Two steps:
     * 1] calculate the magnitude of the angle between the x axis and
     *     the i basis vector.
     * 2] Calculate the sign of theta_i based on the angle between the y axis
     *     and the i basis vector.
     */
    *theta_i = acos(xscale/(*i_mag)) ;  /* magnitude */
    theta_test = acos(yskew/(*i_mag)) ; /* sign */
    if (theta_test < M_PI_2){
        *theta_i = -(*theta_i) ;
    }


    /* Angular separation of basis vectors
     * ===================================
     * Two steps:
     * 1] calculate the magnitude of the angle between the j basis vector and
     *     the i basis vector.
     * 2] Calculate the sign of theta_ij based on the angle between the
     *    perpendicular of the i basis vector and the j basis vector.
     */
    *theta_ij = acos(((xscale*xskew) + (yskew*yscale))/((*i_mag)*(*j_mag))) ;
    theta_test = acos( ((-yskew*xskew)+(xscale*yscale)) /
            ((*i_mag)*(*j_mag)));
    if (theta_test > M_PI_2) {
        *theta_ij = -(*theta_ij) ;
    }
}

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