从 R 查询 SQL Server 地理空间数据 [英] Querying SQL Server geospatial data from R

问题描述

已我已将登录详细信息添加到演示 SQL Server 2017 中.

Edited: I have added login details to a demo SQL Server 2017.

我正在使用 FreeTDS 驱动程序从 R 查询 SQL Server(优先于 Microsoft odbc 驱动程序，因为它支持 Linux 中的 Windows 身份验证).

I am querying an SQL Server from R using the FreeTDS driver (preferred over the Microsoft odbc driver as it supports Windows authentication in Linux).

我正在努力用 st_read 解释几何列.

I'm struggling to interpret the geometry column with st_read.

连接是这样发起的:

library(odbc)
library(DBI)
library(sf)

username <- 'SO-user'
sql_server_ip <- '35.214.169.110'
password <- 'SQLaskingfortrouble?!'

con <- dbConnect(odbc(),
                 Driver = "FreeTDS",
                 Server = sql_server_ip,
                 Database = "stackoverflow-example",
                 UID = username,
                 PWD = password,
                 Port = 1433)
# I have also tried Driver = "ODBC Driver 17 for SQL Server"

查询结果如下:

data <- dbGetQuery(con, 'SELECT TOP 2
                         objectid, geom,
                         geom.STGeometryType() geom_type,
                         geom.STSrid STSrid
                         FROM spatialdata')

objectid    geom          geom_type     stsRID
864         blob[416 B]   LineString    25832
865         blob[416 B]   LineString    25832

class(data$geom)
"blob" "vctrs_list_of" "vctrs_vctr"   

原始/斑点几何看起来像十六进制:

The raw/blob geometry looks like hex:

rawToHex(data$geom[1])
e86400000104180000004003780b38331f416b4df3ea9ecf5741a04c150c38331f4159ca32f09ecf574160ba...

尝试使用 st_read，所以我可以从中得到一个有用的 sf 数据帧，根据我传递给函数的选项，给了我一系列错误消息:

Trying to use st_read, so I can get a useful sf dataframe out of it, gives me a range of error messages, depending on the options I pass to the function:

st_read(con, geometry_column = "geom", 
        query = "SELECT TOP 10 objectid, geom FROM \"spatialdata\"")

Error: nanodbc/nanodbc.cpp:1617: 00000: [FreeTDS][SQL Server]Invalid object name 'spatial_ref_sys'.  [FreeTDS][SQL Server]Statement(s) could not be prepared. 
<SQL> 'select srtext from spatial_ref_sys where srid = 70647808'
In addition: Warning message:
In CPL_crs_from_input(x) :
  GDAL Error 6: EPSG PCS/GCS code 70647808 not found in EPSG support files.  Is this a valid EPSG coordinate system?

看起来 EPSG (25832) 没有被正确识别.

It looks like the EPSG (25832) is not being recognised correctly.

在我的例子中 st_read 的正确构造是什么?

What is the correct construction of st_read in my case?

额外问题:如何将边界框有效地附加到 st_read?

Bonus question: How can a bounding box be efficiently appended to st_read?

推荐答案

您是否尝试过 WKB 表示法?

Have you tried the WKB representation?

mytest <- st_read(con, geometry_column = "geom", 
                         query = "
select geometry::STGeomFromText('POLYGON ((0 0, 1.5 0, 1.5 1.5, 0 1.5, 0 0))', 0).STAsBinary() as geom
union all
select geometry::Parse('CIRCULARSTRING(0 0, 1 1.10, 2 2.3246, 0 7, -3 2.3246, -1 2.1082, 0 0)').STAsBinary() as geom;
")

plot(mytest)

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