point_interpolate()

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

inline

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 316 of file lwlinearreferencing.c.

{
        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 PARANOIA_LEVEL > 0
        if (!(ordinate == 'X' || ordinate == 'Y' || ordinate == 'Z' || ordinate == 'M'))
        {
                lwerror("Cannot interpolate over %c ordinate.", ordinate);
                return LW_FAILURE;
        }
 
        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 LW_FAILURE;
        }
#endif
 
        proportion = (interpolation_value - p1_value) / (p2_value - p1_value);
 
        for (i = 0; i < 4; i++)
        {
                if (dims[i] == 'Z' && !hasz)
                        continue;
                if (dims[i] == 'M' && !hasm)
                        continue;
                if (dims[i] == ordinate)
                        lwpoint_set_ordinate(p, dims[i], interpolation_value);
                else
                {
                        double newordinate = 0.0;
                        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);
                }
        }
 
        return LW_SUCCESS;
}

References FP_MAX, FP_MIN, LW_FAILURE, LW_SUCCESS, lwerror(), lwpoint_get_ordinate(), and lwpoint_set_ordinate().

Referenced by lwline_clip_to_ordinate_range(), ptarray_clamp_to_ordinate_range(), and test_point_interpolate().

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