背景
PolarDB 的云原生存算分离架构, 具备低廉的数据存储、高效扩展弹性、高速多机并行计算能力、高速数据搜索和处理; PolarDB与计算算法结合, 将实现双剑合璧, 推动业务数据的价值产出, 将数据变成生产力.
本文将介绍PolarDB 开源版 通过 pgpointcloud 实现高效孪生数据存储和管理 - 支撑工厂、农业等现实世界数字化|数字孪生, 元宇宙相关业务的虚拟现实结合
测试环境为macOS+docker, PolarDB部署请参考下文:
点云部署参考:
pgpointcloud 的特性
pgpointcloud的原理是将很多个点存储到一个值(点集)里面, 点集可以用来表达轨迹、扫描影像, 业务操作通常包含:
- 判断轨迹是否相交(指包住两个轨迹的边界(bound box)是否相交), 实际上使用PostGIS的trajectories可能更适合.
- 判断轨迹是否落到某个给定区域(指轨迹的边界(bound box)是否和指定几何对象是否相交)
- 指定区域将内部的轨迹抠出(将落在指定几何对象内部的点从点集中抠出)
- 合并轨迹
- 压缩轨迹
- 3D建模和数据存储
- 3D影像的抠出
注意这里说的“轨迹”不带时间, 只是为了辅助理解所以称之为轨迹, 实际上pgpointcloud不适合轨迹业务. 轨迹建议使用postgis. 或者阿里云ganos.
pgpointcloud存储点集的优势:
- 支持压缩, 节省成本
- 片存储, 存取效率高
- 支持内置点云操作算法, 同时可扩展算法, 无需提取数据到本地进行计算, 大幅度提升计算效率
- 支持GIS, 方便和地理信息结合, 更好的满足虚拟现实|数字孪生业务需求
- 支持索引, 过滤效率高
例子
1、点
SELECT PC_MakePoint(1, ARRAY[-127, 45, 124.0, 4.0]);
010100000064CEFFFF94110000703000000400 Insert some test values into the points table:
INSERT INTO points (pt)
SELECT PC_MakePoint(1, ARRAY[x,y,z,intensity])
FROM (
SELECT
-127+a/100.0 AS x,
45+a/100.0 AS y,
1.0*a AS z,
a/10 AS intensity
FROM generate_series(1,100) AS a
) AS values; SELECT PC_AsText('010100000064CEFFFF94110000703000000400'::pcpoint);
{"pcid":1,"pt":[-127,45,124,4]} 2、点集
INSERT INTO patches (pa)
SELECT PC_Patch(pt) FROM points GROUP BY id/10; SELECT PC_AsText(PC_MakePatch(1, ARRAY[-126.99,45.01,1,0, -126.98,45.02,2,0, -126.97,45.03,3,0]));
{"pcid":1,"pts":[
[-126.99,45.01,1,0],[-126.98,45.02,2,0],[-126.97,45.03,3,0]
]} SELECT PC_AsText(pa) FROM patches LIMIT 1;
{"pcid":1,"pts":[
[-126.99,45.01,1,0],[-126.98,45.02,2,0],[-126.97,45.03,3,0],
[-126.96,45.04,4,0],[-126.95,45.05,5,0],[-126.94,45.06,6,0],
[-126.93,45.07,7,0],[-126.92,45.08,8,0],[-126.91,45.09,9,0]
]} 3、判断轨迹是否相交(指包住两个轨迹的边界(bound box)是否相交), 实际上使用PostGIS的trajectories可能更适合.
-- Patch should intersect itself
SELECT PC_Intersects(
'01010000000000000001000000C8CEFFFFF8110000102700000A00'::pcpatch,
'01010000000000000001000000C8CEFFFFF8110000102700000A00'::pcpatch);
t 4、判断轨迹是否落到某个给定区域(指轨迹的边界(bound box)是否和指定几何对象是否相交)
SELECT PC_Intersects('SRID=4326;POINT(-126.451 45.552)'::geometry, pa)
FROM patches WHERE id = 7;
t 5、指定区域将内部的轨迹抠出(将落在指定几何对象内部的点从点集中抠出)
SELECT PC_AsText(PC_Explode(PC_Intersection(
pa,
'SRID=4326;POLYGON((-126.451 45.552, -126.42 47.55, -126.40 45.552, -126.451 45.552))'::geometry
)))
FROM patches WHERE id = 7;
pc_astext
--------------------------------------
{"pcid":1,"pt":[-126.44,45.56,56,5]}
{"pcid":1,"pt":[-126.43,45.57,57,5]}
{"pcid":1,"pt":[-126.42,45.58,58,5]}
{"pcid":1,"pt":[-126.41,45.59,59,5]} 6、合并轨迹
聚合函数
-- Compare npoints(sum(patches)) to sum(npoints(patches))
SELECT PC_NumPoints(PC_Union(pa)) FROM patches;
SELECT Sum(PC_NumPoints(pa)) FROM patches;
100 可变函数
create or replace function pcunion (VARIADIC pc pcpatch[]) returns pcpatch as $$
select PC_Union(pa) from unnest(pc) as pa;
$$ language sql strict;
select pcunion(pc1,pc2,...); 7、压缩点集
PC_Compress(p pcpatch,global_compression_scheme text,compression_config text) returns pcpatch Allowed global compression schemes are:
- auto: determined by pcid
- laz: no compression config supported
dimensional: configuration is a comma-separated list of per-dimension compressions from this list
- auto: determined automatically from values stats
- zlib: deflate compression
- sigbits: significant bits removal
- rle: run-length encoding
8、3D影像的抠出
1 PC_FilterGreaterThan
PC_FilterGreaterThan(p pcpatch, dimname text, float8 value) returns pcpatch:
Returns a patch with only points whose values are greater than the supplied value for the requested dimension.
SELECT PC_AsText(PC_FilterGreaterThan(pa, 'y', 45.57))
FROM patches WHERE id = 7;
{"pcid":1,"pts":[[-126.42,45.58,58,5],[-126.41,45.59,59,5]]}
2 PC_FilterLessThan
PC_FilterLessThan(p pcpatch, dimname text, float8 value) returns pcpatch:
Returns a patch with only points whose values are less than the supplied value for the requested dimension.
3 PC_FilterBetween
PC_FilterBetween(p pcpatch, dimname text, float8 value1, float8 value2) returns pcpatch:
Returns a patch with only points whose values are between (excluding) the supplied values for the requested dimension.
4 PC_FilterEquals
PC_FilterEquals(p pcpatch, dimname text, float8 value) returns pcpatch:
Returns a patch with only points whose values are the same as the supplied values for the requested dimension. 9、返回包住点集的几何"bound box"或"bound box的对角线"
通常用于在几何图像上创建geo索引:
SELECT ST_AsText(PC_EnvelopeGeometry(pa)) FROM patches LIMIT 1;
POLYGON((-126.99 45.01,-126.99 45.09,-126.91 45.09,-126.91 45.01,-126.99 45.01))
CREATE INDEX ON patches USING GIST(PC_EnvelopeGeometry(patch)); SELECT ST_AsText(PC_BoundingDiagonalGeometry(pa)) FROM patches;
st_astext
------------------------------------------------
LINESTRING Z (-126.99 45.01 1,-126.91 45.09 9)
LINESTRING Z (-126 46 100,-126 46 100)
LINESTRING Z (-126.2 45.8 80,-126.11 45.89 89)
LINESTRING Z (-126.4 45.6 60,-126.31 45.69 69)
LINESTRING Z (-126.3 45.7 70,-126.21 45.79 79)
LINESTRING Z (-126.8 45.2 20,-126.71 45.29 29)
LINESTRING Z (-126.5 45.5 50,-126.41 45.59 59)
LINESTRING Z (-126.6 45.4 40,-126.51 45.49 49)
LINESTRING Z (-126.9 45.1 10,-126.81 45.19 19)
LINESTRING Z (-126.7 45.3 30,-126.61 45.39 39)
LINESTRING Z (-126.1 45.9 90,-126.01 45.99 99)
CREATE INDEX ON patches USING GIST(PC_BoundingDiagonalGeometry(patch) gist_geometry_ops_nd); pgpointcloud 函数接口解读
1、点
PC_MakePoint(pcid integer, vals float8[]) returns pcpoint:
- 构建点, pcid为schema, 相同schema可以表达为某一类点
PC_AsText(p pcpoint) returns text:
- 将二进制点转换成text表达
PC_PCId(p pcpoint) returns integer (from 1.1.0):
- 获取点的schema id
PC_Get(pt pcpoint) returns float8[]:
- 获取点的所有维度值
PC_Get(pt pcpoint, dimname text) returns numeric:
- 获取指定维度值: x,y,z,Intensity
PC_MemSize(pt pcpoint) returns int4:
- 点占据内存大小
2、点集
PC_Patch(pts pcpoint[]) returns pcpatch:
- 将多个点聚合为点集
PC_MakePatch(pcid integer, vals float8[]) returns pcpatch:
- 构造点集
PC_NumPoints(p pcpatch) returns integer:
- 返回点集中有多少点
PC_PCId(p pcpatch) returns integer:
- 返回点集的schema id
PC_AsText(p pcpatch) returns text:
- 将点集二进制格式转换为文本格式
PC_Summary(p pcpatch) returns text (from 1.1.0):
- 返回点集的统计信息: 点个数, srid, 各个维度的avg,min,max统计等
PC_Uncompress(p pcpatch) returns pcpatch:
- 解压点集
PC_Union(p pcpatch[]) returns pcpatch:
- 将多个点集聚合为一个点集
PC_Intersects(p1 pcpatch, p2 pcpatch) returns boolean:
- 判断两个点集的bound box是否相交
PC_Explode(p pcpatch) returns SetOf[pcpoint]:
- 将点集展开为点(返回多条记录)
PC_PatchAvg(p pcpatch, dimname text) returns numeric:
- 返回点集指定维度的平均值
PC_PatchMax(p pcpatch, dimname text) returns numeric:
- 返回点集指定维度的最大值
PC_PatchMin(p pcpatch, dimname text) returns numeric:
- 返回点集指定维度的最小值
PC_PatchMin(p pcpatch) returns pcpoint:
- 返回点集所有维度的最小值
PC_PatchAvg(p pcpatch) returns pcpoint:
- 返回点集所有维度的平均值
PC_PatchMax(p pcpatch) returns pcpoint:
- 返回点集所有维度的最大值
PC_FilterGreaterThan(p pcpatch, dimname text, float8 value) returns pcpatch:
- 过滤在某个‘指定维度’上大于‘指定’的点, 构成一个新的点集返回
PC_FilterLessThan(p pcpatch, dimname text, float8 value) returns pcpatch:
- 过滤在某个‘指定维度’上小于‘指定值’的点, 构成一个新的点集返回
PC_FilterBetween(p pcpatch, dimname text, float8 value1, float8 value2) returns pcpatch:
- 过滤在某个‘指定维度’上落在某‘指定值’范围内的点, 构成一个新的点集返回
PC_FilterEquals(p pcpatch, dimname text, float8 value) returns pcpatch:
- 过滤在某个‘指定维度’上等于‘指定值’的点, 构成一个新的点集返回
PC_Compress(p pcpatch,global_compression_scheme text,compression_config text) returns pcpatch:
- 压缩点集
PC_PointN(p pcpatch, n int4) returns pcpoint:
- 返回点集内的第N个点
PC_IsSorted(p pcpatch, dimnames text[], strict boolean default true) returns boolean:
- 判断点集在某些维度上是否有序
PC_Sort(p pcpatch, dimnames text[]) returns pcpatch:
- 对点集按指定维度排序. 有点像电子管电视机的扫描顺序的概念
PC_Range(p pcpatch, start int4, n int4) returns pcpatch:
- 返回点集中指定区间的点
PC_SetPCId(p pcpatch, pcid int4, def float8 default 0.0) returns pcpatch:
- 设置点集的schema id
PC_Transform(p pcpatch, pcid int4, def float8 default 0.0) returns pcpatch:
- 转换点集schema id
PC_MemSize(p pcpatch) returns int4:
- 返回点集内存占用
3、GIS互动
PC_Intersects(p pcpatch, g geometry) returns boolean:
PC_Intersects(g geometry, p pcpatch) returns boolean:
- 判断点集的bound box是否与几何对象交叉
PC_Intersection(pcpatch, geometry) returns pcpatch:
- 提取点集内落在几何对象内的点构成新点集并返回
Geometry(pcpoint) returns geometry:
pcpoint::geometry returns geometry:
- 将点转换为几何对象
PC_EnvelopeGeometry(pcpatch) returns geometry:
- 提取点集的bound box, 返回由bound box四个点组成的polygon
PC_BoundingDiagonalGeometry(pcpatch) returns geometry:
- 提取点集的bound box, 返回由bound box左下和右上点组成的对角线段
详细参考:
https://pgpointcloud.github.io/pointcloud/functions/index.html
