如何使用bigquery在另一个多边形内创建多种尺寸的方框多边形

Question

我正在尝试创建位于较大多边形（蓝色多边形）内的方形随机多边形（红色框）的序列，给定较大多边形的几何形状。我怎样才能在大查询中实现这一点。我也

我尝试了

ST_MAKEENVELOP()

，但在BQ中没有找到，还有ST_XMIN和ST_XMAX

Answer 1

考虑以下方法 - 它应该是您了解确切用例的良好起点！

WITH input AS (
  SELECT geo_code, city_geom, ST_BOUNDINGBOX(city_geom) box
  FROM `bigquery-public-data.utility_us.us_cities_area`
  WHERE geo_code = '51445'
), grid AS (
  SELECT geo_code, city_geom, 
    box.xmin + x * (box.xmax - box.xmin) / num_cols AS x_min,
    box.xmin + (x + 1) * (box.xmax - box.xmin) / num_cols AS x_max,
    box.ymin + y * (box.ymax - box.ymin) / num_rows AS y_min,
    box.ymin + (y + 1) * (box.ymax - box.ymin) / num_rows AS y_max
  FROM input, UNNEST([STRUCT(20 AS num_cols, 20 AS num_rows)]),
  UNNEST(GENERATE_ARRAY(0, num_cols - 1)) AS x, UNNEST(GENERATE_ARRAY(0, num_rows - 1)) AS y
)
SELECT ANY_VALUE(city_geom) city_geom, ST_UNION_AGG(smaller_box) boxes FROM (
  SELECT geo_code, city_geom, smaller_box FROM (
    SELECT geo_code, city_geom, 
      ST_GEOGFROM(FORMAT('POLYGON((%f %f, %f %f, %f %f, %f %f, %f %f))', 
        x_min, y_min, x_min, y_max, x_max, y_max, x_max, y_min, x_min, y_min)) AS smaller_box
    FROM grid
  )
  WHERE ST_WITHIN(smaller_box, city_geom)
  ORDER BY RAND()
  LIMIT 10
)
GROUP BY geo_code    

有输出

如下图所示