ptarray_to_twkb_buf()

static int ptarray_to_twkb_buf ( const POINTARRAY *  pa, TWKB_GLOBALS *  globals, TWKB_STATE *  ts, int  register_npoints, uint32_t  minpoints  )

static

Stores a pointarray as varints in the buffer @register_npoints, controls whether an npoints entry is added to the buffer (used to skip npoints for point types) @dimension, states the dimensionality of object this array is part of (0 = point, 1 = linear, 2 = areal)

Definition at line 106 of file lwout_twkb.c.

{
        uint32_t ndims = FLAGS_NDIMS(pa->flags);
        uint32_t i, j;
        bytebuffer_t b;
        bytebuffer_t *b_p;
        int64_t nextdelta[MAX_N_DIMS];
        int npoints = 0;
        size_t npoints_offset = 0;
        uint32_t max_points_left = pa->npoints;
 
        LWDEBUGF(2, "Entered %s", __func__);
 
        /* Dispense with the empty case right away */
        if ( pa->npoints == 0 && register_npoints )
        {
                LWDEBUGF(4, "Register npoints:%d", pa->npoints);
                bytebuffer_append_uvarint(ts->geom_buf, pa->npoints);
                return 0;
        }
 
        /* If npoints is more than 127 it is unpredictable how many bytes npoints will need */
        /* Then we have to store the deltas in a temp buffer to later add them after npoints */
        /* If noints is below 128 we know 1 byte will be needed */
        /* Then we can make room for that 1 byte at once and write to */
        /* ordinary buffer */
        if( pa->npoints > 127 )
        {
                /* Independent buffer to hold the coordinates, so we can put the npoints */
                /* into the stream once we know how many points we actually have */
                bytebuffer_init_with_size(&b, 3 * ndims * pa->npoints);
                b_p = &b;
        }
        else
        {
                /* We give an alias to our ordinary buffer */
                b_p = ts->geom_buf;
                if ( register_npoints )
                {
                        /* We do not store a pointer to the place where we want the npoints value */
                        /* Instead we store how far from the beginning of the buffer we want the value */
                        /* That is because we otherwise will get in trouble if the buffer is reallocated */
                        npoints_offset = b_p->writecursor - b_p->buf_start;
 
                        /* We just move the cursor 1 step to make room for npoints byte */
                        /* We use the function append_byte even if we have no value yet, */
                        /* since that gives us the check for big enough buffer and moves the cursor */
                        bytebuffer_append_byte(b_p, 0);
                }
        }
 
        for ( i = 0; i < pa->npoints; i++ )
        {
                double *dbl_ptr = (double*)getPoint_internal(pa, i);
                int64_t diff = 0;
 
                /* Write this coordinate to the buffer as a varint */
                for ( j = 0; j < ndims; j++ )
                {
                        /* To get the relative coordinate we don't get the distance */
                        /* from the last point but instead the distance from our */
                        /* last accumulated point. This is important to not build up an */
                        /* accumulated error when rounding the coordinates */
                        nextdelta[j] = (int64_t) llround(globals->factor[j] * dbl_ptr[j]) - ts->accum_rels[j];
                        LWDEBUGF(4, "deltavalue: %d, ", nextdelta[j]);
                        diff += llabs(nextdelta[j]);
                }
 
                /* Skipping the first point is not allowed */
                /* If the sum(abs()) of all the deltas was zero, */
                /* then this was a duplicate point, so we can ignore it */
                if ( i > 0 && diff == 0 && max_points_left > minpoints )
                {
                        max_points_left--;
                        continue;
                }
 
                /* We really added a point, so... */
                npoints++;
 
                /* Write this vertex to the temporary buffer as varints */
                for ( j = 0; j < ndims; j++ )
                {
                        ts->accum_rels[j] += nextdelta[j];
                        bytebuffer_append_varint(b_p, nextdelta[j]);
                }
 
                /* See if this coordinate expands the bounding box */
                if( globals->variant & TWKB_BBOX )
                {
                        for ( j = 0; j < ndims; j++ )
                        {
                                if( ts->accum_rels[j] > ts->bbox_max[j] )
                                        ts->bbox_max[j] = ts->accum_rels[j];
 
                                if( ts->accum_rels[j] < ts->bbox_min[j] )
                                        ts->bbox_min[j] = ts->accum_rels[j];
                        }
                }
 
        }
 
        if ( pa->npoints > 127 )
        {
                /* Now write the temporary results into the main buffer */
                /* First the npoints */
                if ( register_npoints )
                        bytebuffer_append_uvarint(ts->geom_buf, npoints);
                /* Now the coordinates */
                bytebuffer_append_bytebuffer(ts->geom_buf, b_p);
 
                /* Clear our temporary buffer */
                bytebuffer_destroy_buffer(&b);
        }
        else
        {
                /* If we didn't use a temp buffer, we just write that npoints value */
                /* to where it belongs*/
                if ( register_npoints )
                        varint_u64_encode_buf(npoints, b_p->buf_start + npoints_offset);
        }
 
        return 0;
}

References TWKB_STATE::accum_rels, TWKB_STATE::bbox_max, TWKB_STATE::bbox_min, bytebuffer_t::buf_start, bytebuffer_append_byte(), bytebuffer_append_bytebuffer(), bytebuffer_append_uvarint(), bytebuffer_append_varint(), bytebuffer_destroy_buffer(), bytebuffer_init_with_size(), TWKB_GLOBALS::factor, POINTARRAY::flags, FLAGS_NDIMS, TWKB_STATE::geom_buf, getPoint_internal(), LWDEBUGF, MAX_N_DIMS, POINTARRAY::npoints, TWKB_BBOX, TWKB_GLOBALS::variant, varint_u64_encode_buf(), and bytebuffer_t::writecursor.

Referenced by lwline_to_twkb_buf(), lwpoint_to_twkb_buf(), and lwpoly_to_twkb_buf().

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