Group by value and create geography polyline from points (latitude and longitude) for each group in T-SQL

问题

A similar question has been asked here:

Create geography polyline from points in T-SQL

Taking that question further, I have a table schema that looks like this:

CREATE TABLE [dbo].[LongAndLats](
[Longitude] [float] NULL,
[Latitude] [float] NULL,
[SortOrder] [bigint] NULL,
[SensorID] [bigint] NULL,
)

Sample data looks like this:

How can I convert these points into a geography polyline for each SensorID using TSQL (so that I would have a SensorID/Polyline record for each SensorID)?

I've tried using a db_cursor but I get a separate result set for each group (and I think the geographies might be the same). This code:

DECLARE @SensorID VARCHAR(2000)
DECLARE @LineFromPoints geography
DECLARE @BuildString NVARCHAR(MAX)

DECLARE db_cursor CURSOR FOR  
SELECT Distinct([SensorId]) 
FROM [dbo].[LongAndLats]

OPEN db_cursor   
FETCH NEXT FROM db_cursor INTO LongAndLats 

WHILE @@FETCH_STATUS = 0   
BEGIN   
       SELECT @BuildString = COALESCE(@BuildString + ',', '') + CAST([Longitude] AS NVARCHAR(50)) + ' ' + CAST([Latitude] AS NVARCHAR(50))
       FROM [LongAndLats]
       WHERE SensorID = @SensorID
       ORDER BY SortOrder            

       SET @BuildString = 'LINESTRING(' + @BuildString + ')';   
       SET @LineFromPoints = geography::STLineFromText(@BuildString, 4326);
       SELECT @LineFromPoints As 'Geomerty', @name As 'SensorID' 

       FETCH NEXT FROM db_cursor INTO @name   
END   

CLOSE db_cursor   
DEALLOCATE db_cursor

Results in this:

Ultimately, I'd like to have a view returning all of the SensorID/Polyline pairs. I don't know that my current approach is going to work. I would appreciate any suggestions or examples.

回答1:

From SQL Server 2017+ you could use:

SELECT geography::STLineFromText('LINESTRING(' + 
         STRING_AGG(CONCAT(Longitude, ' ' ,Latitude), ',') 
         WITHIN GROUP(ORDER BY SortOrder) + ')' , 4326) AS geometry
      ,SensorId
FROM dbo.LongAndLats
GROUP BY SensorId
HAVING COUNT(*) > 1;

DBFiddle Demo

I've tried using a db_cursor but I get a separate result set for each group

Please avoid cursors, end each line with semicolon and stop using:

SELECT @BuildString = COALESCE(@BuildString + ',', '') 
       + CAST([Longitude] AS NVARCHAR(50)) + ' ' + CAST([Latitude] 
        AS NVARCHAR(50))
FROM [LongAndLats]
WHERE SensorID = @SensorID
ORDER BY SortOrder;

Construct above may look ok, but it could lead to undefined behaviour. More info: nvarchar concatenation / index / nvarchar(max) inexplicable behavior

EDIT:

SQL Server 2012 version:

SELECT geography::STLineFromText('LINESTRING(' 
      + STUFF(
             (SELECT ',' + CONCAT(Longitude, ' ' ,Latitude) 
              FROM dbo.LongAndLats t2
              WHERE t1.SensorId = t2.SensorId 
              ORDER BY SortOrder
              FOR XML PATH (''))
             , 1, 1, '')
       + ')' 
       , 4326) AS geometry, SensorId
FROM dbo.LongAndLats t1
GROUP BY SensorId
HAVING COUNT(*) > 1;

DBFiddle Demo2

EDIT2:

To avoid:

A .NET Framework error occurred during execution of user-defined routine or aggregate "geography":

System.FormatException: 24117: The LineString input is not valid because it does not have enough points. A LineString must have at least two points.

you could add HAVING COUNT(*) > 1;

FINAL EDIT:

If you have "garbage data", just filter it out(or add CHECK constraint on that column):

"Latitude values must be between -90 and 90 degrees"

SELECT geography::STLineFromText('LINESTRING(' 
      + STUFF(
             (SELECT ',' + CONCAT(Longitude, ' ' ,Latitude) 
              FROM dbo.LongAndLats t2
              WHERE t1.SensorId = t2.SensorId 
                AND Latitude BETWEEN -90 and 90
                AND Longitude BETWEEN -180 AND 180
              ORDER BY SortOrder
              FOR XML PATH (''))
             , 1, 1, '')
       + ')' 
       , 4326) AS geometry, SensorId
FROM dbo.LongAndLats t1
WHERE Latitude BETWEEN -90 and 90
  AND Longitude BETWEEN -180 AND 180
GROUP BY SensorId
HAVING COUNT(*) > 1;

DBFiddle Demo3

来源：https://stackoverflow.com/questions/48241483/group-by-value-and-create-geography-polyline-from-points-latitude-and-longitude

标签

sql-server

tsql

geospatial

sqlgeography

sqlgeometry