lwline_measured_from_lwline()

LWLINE* lwline_measured_from_lwline	(	const LWLINE *	lwline,
		double	m_start,
		double	m_end
	)

Re-write the measure ordinate (or add one, if it isn't already there) interpolating the measure between the supplied start and end values.

Add a measure dimension to a line, interpolating linearly from the start to the end value.

Definition at line 388 of file lwline.c.

{
        int i = 0;
        int hasm = 0, hasz = 0;
        int npoints = 0;
        double length = 0.0;
        double length_so_far = 0.0;
        double m_range = m_end - m_start;
        double m;
        POINTARRAY *pa = NULL;
        POINT3DZ p1, p2;
 
        if ( lwline->type != LINETYPE )
        {
                lwerror("lwline_construct_from_lwline: only line types supported");
                return NULL;
        }
 
        hasz = FLAGS_GET_Z(lwline->flags);
        hasm = 1;
 
        /* Null points or npoints == 0 will result in empty return geometry */
        if ( lwline->points )
        {
                npoints = lwline->points->npoints;
                length = ptarray_length_2d(lwline->points);
                getPoint3dz_p(lwline->points, 0, &p1);
        }
 
        pa = ptarray_construct(hasz, hasm, npoints);
 
        for ( i = 0; i < npoints; i++ )
        {
                POINT4D q;
                POINT2D a, b;
                getPoint3dz_p(lwline->points, i, &p2);
                a.x = p1.x;
                a.y = p1.y;
                b.x = p2.x;
                b.y = p2.y;
                length_so_far += distance2d_pt_pt(&a, &b);
                if ( length > 0.0 )
                        m = m_start + m_range * length_so_far / length;
                /* #3172, support (valid) zero-length inputs */
                else if ( length == 0.0 && npoints > 1 )
                        m = m_start + m_range * i / (npoints-1);
                else
                        m = 0.0;
                q.x = p2.x;
                q.y = p2.y;
                q.z = p2.z;
                q.m = m;
                ptarray_set_point4d(pa, i, &q);
                p1 = p2;
        }
 
        return lwline_construct(lwline->srid, NULL, pa);
}

References distance2d_pt_pt(), LWLINE::flags, FLAGS_GET_Z, getPoint3dz_p(), LINETYPE, lwerror(), lwline_construct(), POINT4D::m, POINTARRAY::npoints, LWLINE::points, ptarray_construct(), ptarray_length_2d(), ptarray_set_point4d(), LWLINE::srid, LWLINE::type, POINT2D::x, POINT3DZ::x, POINT4D::x, POINT2D::y, POINT3DZ::y, POINT4D::y, POINT3DZ::z, and POINT4D::z.

Referenced by lwline_locate_along(), lwmline_measured_from_lwmline(), and ST_AddMeasure().

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