SQLite

  if( z[j-1]<'0' ) return 0;
  if( pVal ) *pVal = atof((const char*)p->z);
  p->z += j;
  return 1;
}

/*
** If the input is a well-formed JSON array of coordinates with at least
** four coordinates and where each coordinate is itself a two-value array,
** then convert the JSON into a GeoPoly object and return a pointer to
** that object.
**
** If any error occurs, return NULL.
*/
static GeoPoly *geopolyParseJson(const unsigned char *z, int *pRc){
  GeoParse s;
  int rc = SQLITE_OK;
  memset(&s, 0, sizeof(s));

      }
      while( geopolyParseNumber(&s, ii<=1 ? &s.a[s.nVertex*2+ii] : 0) ){
        ii++;
        if( ii==2 ) s.nVertex++;
        c = geopolySkipSpace(&s);
        s.z++;
        if( c==',' ) continue;
        if( c==']' && ii>=2 ) break;
        s.nErr++;
        rc = SQLITE_ERROR;
        goto parse_json_err;
      }
      if( geopolySkipSpace(&s)==',' ){
        s.z++;
        continue;
      }
      break;
    }
    if( geopolySkipSpace(&s)==']'
     && s.nVertex>=4
     && (s.z++, geopolySkipSpace(&s)==0)
    ){
      int nByte;
      GeoPoly *pOut;
      int x = (s.nVertex-1)*2;
      if( s.a[x]==s.a[0] && s.a[x+1]==s.a[1] ) s.nVertex--;
      nByte = sizeof(GeoPoly) * (s.nVertex-1)*2*sizeof(GeoCoord);
      pOut = sqlite3_malloc64( nByte );
      x = 1;

      }
    }
    if( pRc ) *pRc = SQLITE_OK;
    return p;
  }else if( sqlite3_value_type(pVal)==SQLITE_TEXT ){
    return geopolyParseJson(sqlite3_value_text(pVal), pRc);
  }else{
    if( pRc ) *pRc = SQLITE_ERROR;
    if( pCtx!=0 ) sqlite3_result_error(pCtx, "not a valid polygon", -1);
    return 0;
  }
}

/*
** Implementation of the geopoly_blob(X) function.

    rc = nodeAcquire(pRtree, 1, 0, &pRoot);
    if( rc==SQLITE_OK && idxNum<=3 ){
      RtreeCoord bbox[4];
      RtreeConstraint *p;
      assert( argc==1 );
      geopolyBBox(0, argv[0], bbox, &rc);
      if( rc ){
        goto geopoly_filter_end;
      }
      pCsr->aConstraint = p = sqlite3_malloc(sizeof(RtreeConstraint)*4);
      pCsr->nConstraint = 4;
      if( p==0 ){
        rc = SQLITE_NOMEM;
      }else{
        memset(pCsr->aConstraint, 0, sizeof(RtreeConstraint)*4);

          p->u.rValue = bbox[3].f;
        }
      }
    }
    if( rc==SQLITE_OK ){
      RtreeSearchPoint *pNew;
      pNew = rtreeSearchPointNew(pCsr, RTREE_ZERO, (u8)(pRtree->iDepth+1));
      if( pNew==0 ){
        rc = SQLITE_NOMEM;
        goto geopoly_filter_end;
      }
      pNew->id = 1;
      pNew->iCell = 0;
      pNew->eWithin = PARTLY_WITHIN;
      assert( pCsr->bPoint==1 );
      pCsr->aNode[0] = pRoot;
      pRoot = 0;
      RTREE_QUEUE_TRACE(pCsr, "PUSH-Fm:");
      rc = rtreeStepToLeaf(pCsr);
    }
  }

geopoly_filter_end:
  nodeRelease(pRtree, pRoot);
  rtreeRelease(pRtree);
  return rc;
}

/*
** Rtree virtual table module xBestIndex method. There are three

  ){
    geopolyBBox(0, aData[2], cell.aCoord, &rc);
    if( rc ){
      if( rc==SQLITE_ERROR ){
        pVtab->zErrMsg =
          sqlite3_mprintf("_shape does not contain a valid polygon");
      }
      goto geopoly_update_end;
    }
    coordChange = 1;

    /* If a rowid value was supplied, check if it is already present in 
    ** the table. If so, the constraint has failed. */
    if( newRowidValid ){
      int steprc;

    }
    if( nChange ){
      sqlite3_step(pUp);
      rc = sqlite3_reset(pUp);
    }
  }

geopoly_update_end:
  rtreeRelease(pRtree);
  return rc;
}

/*
** Report that geopoly_overlap() is an overloaded function suitable
** for use in xBestIndex.