point_interpolate()

int point_interpolate	(	const POINT4D *	p1,
		const POINT4D *	p2,
		POINT4D *	p,
		int	hasz,
		int	hasm,
		char	ordinate,
		double	interpolation_value
	)

Given two points, a dimensionality, an ordinate, and an interpolation value generate a new point that is proportionally between the input points, using the values in the provided dimension as the scaling factors.

Definition at line 321 of file lwlinearreferencing.c.

References FP_MAX, FP_MIN, LWDEBUGF, lwerror(), lwpoint_get_ordinate(), and lwpoint_set_ordinate().

Referenced by lwline_clip_to_ordinate_range(), and test_point_interpolate().

{
        static char* dims = "XYZM";
        double p1_value = lwpoint_get_ordinate(p1, ordinate);
        double p2_value = lwpoint_get_ordinate(p2, ordinate);
        double proportion;
        int i = 0;

        if ( ! ( ordinate == 'X' || ordinate == 'Y' || ordinate == 'Z' || ordinate == 'M' ) )
        {
                lwerror("Cannot set %c ordinate.", ordinate);
                return 0;
        }

        if ( FP_MIN(p1_value, p2_value) > interpolation_value ||
                FP_MAX(p1_value, p2_value) < interpolation_value )
        {
                lwerror("Cannot interpolate to a value (%g) not between the input points (%g, %g).", interpolation_value, p1_value, p2_value);
                return 0;
        }

        proportion = fabs((interpolation_value - p1_value) / (p2_value - p1_value));

        for ( i = 0; i < 4; i++ )
        {
                double newordinate = 0.0;
                if ( dims[i] == 'Z' && ! hasz ) continue;
                if ( dims[i] == 'M' && ! hasm ) continue;
                p1_value = lwpoint_get_ordinate(p1, dims[i]);
                p2_value = lwpoint_get_ordinate(p2, dims[i]);
                newordinate = p1_value + proportion * (p2_value - p1_value);
                lwpoint_set_ordinate(p, dims[i], newordinate);
                LWDEBUGF(4, "   clip ordinate(%c) p1_value(%g) p2_value(%g) proportion(%g) newordinate(%g) ", dims[i], p1_value, p2_value, proportion, newordinate );
        }

        return 1;
}

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