lwline_interpolate_points()

POINTARRAY * lwline_interpolate_points	(	const LWLINE *	line,
		double	length_fraction,
		char	repeat
	)

Interpolate one or more points along a line.

Definition at line 538 of file lwline.c.

                                                                                               {
        POINT4D pt;
        uint32_t i;
        uint32_t points_to_interpolate;
        uint32_t points_found = 0;
        double length;
        double length_fraction_increment = length_fraction;
        double length_fraction_consumed = 0;
        char has_z = (char) lwgeom_has_z(lwline_as_lwgeom(line));
        char has_m = (char) lwgeom_has_m(lwline_as_lwgeom(line));
        const POINTARRAY* ipa = line->points;
        POINTARRAY* opa;
 
        /* Empty.InterpolatePoint == Point Empty */
        if ( lwline_is_empty(line) )
        {
                return ptarray_construct_empty(has_z, has_m, 0);
        }
 
        /* If distance is one of the two extremes, return the point on that
         * end rather than doing any computations
         */
        if ( length_fraction == 0.0 || length_fraction == 1.0 )
        {
                if ( length_fraction == 0.0 )
                        getPoint4d_p(ipa, 0, &pt);
                else
                        getPoint4d_p(ipa, ipa->npoints-1, &pt);
 
                opa = ptarray_construct(has_z, has_m, 1);
                ptarray_set_point4d(opa, 0, &pt);
 
                return opa;
        }
 
        /* Interpolate points along the line */
        length = ptarray_length_2d(ipa);
        points_to_interpolate = repeat ? (uint32_t) floor(1 / length_fraction) : 1;
        opa = ptarray_construct(has_z, has_m, points_to_interpolate);
 
        const POINT2D* p1 = getPoint2d_cp(ipa, 0);
        for ( i = 0; i < ipa->npoints - 1 && points_found < points_to_interpolate; i++ )
        {
                const POINT2D* p2 = getPoint2d_cp(ipa, i+1);
                double segment_length_frac = distance2d_pt_pt(p1, p2) / length;
 
                /* If our target distance is before the total length we've seen
                 * so far. create a new point some distance down the current
                 * segment.
                 */
                while ( length_fraction < length_fraction_consumed + segment_length_frac && points_found < points_to_interpolate )
                {
                        POINT4D p1_4d = getPoint4d(ipa, i);
                        POINT4D p2_4d = getPoint4d(ipa, i+1);
 
                        double segment_fraction = (length_fraction - length_fraction_consumed) / segment_length_frac;
                        interpolate_point4d(&p1_4d, &p2_4d, &pt, segment_fraction);
                        ptarray_set_point4d(opa, points_found++, &pt);
                        length_fraction += length_fraction_increment;
                }
 
                length_fraction_consumed += segment_length_frac;
 
                p1 = p2;
        }
 
        /* Return the last point on the line. This shouldn't happen, but
         * could if there's some floating point rounding errors. */
        if (points_found < points_to_interpolate) {
                getPoint4d_p(ipa, ipa->npoints - 1, &pt);
                ptarray_set_point4d(opa, points_found, &pt);
        }
 
    return opa;
}

References distance2d_pt_pt(), getPoint2d_cp(), getPoint4d(), getPoint4d_p(), interpolate_point4d(), lwgeom_has_m(), lwgeom_has_z(), lwline_as_lwgeom(), lwline_is_empty(), POINTARRAY::npoints, LWLINE::points, ptarray_construct(), ptarray_construct_empty(), ptarray_length_2d(), and ptarray_set_point4d().

Referenced by LWGEOM_line_interpolate_point(), and test_lwline_interpolate_points().

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