如何从 SQL Server 2008 地理线获取纬度经度？

Question

I'm new to the mapping world and I'm trying to convert a SQL Server geography line column back into it's latitude \\ longitude points to draw on a map.

The line is being set like this

Set @GeoPoly = geography::STGeomFromText('LINESTRING('+@Polyline+')',4326)

Anyone know how to do this? Thanks in advance

Answer 1

I had luck with this:

DECLARE @g geography;
SET @g = geography::STLineFromText(
   'LINESTRING(-122.360 47.656, -122.343 47.656 )'
    , 4326
); 
SELECT @g.STPointN(1).ToString(), @g.STPointN(2).ToString();

Answer 2

Does your LineString consist of only one straight line segment connecting two points? If so, you can retrieve the latitude and longitude of those points as:

SELECT
  @GeoPoly.STStartPoint.Lat AS Start_Lat,
  @GeoPoly.STStartPoint.Long AS Start_Long,
  @GeoPoly.STEndPoint.Lat AS End_Lat,
  @GeoPoly.STEndPoint.Long AS End_Long;

If your LineString consists of multiple line segments connecting a series of points then you can retrieve the Well-Known Text representation using the ToString() method, and then parse the resulting string into coordinate pairs by splitting on commas:

SELECT @GeoPoly.ToString()

The result will be in the format: LINESTRING(Lon1 Lat1, Lon2, Lat2, .... , Lonn, Latn)

Answer 3

You can achieve this in a query by combining STasText(), STRING_SPLIT(), CROSS APPLY and STRING_AGG(). Here is an example query:

WITH Links AS (
    SELECT Id, REPLACE(REPLACE(PosList.STAsText(), 'LINESTRING (', ''), ')', '') as points_string
    FROM LinkSequenceProjections
    WHERE ImportFileId = 1
    AND Id < 5
)
, Points AS (
    SELECT Id, ltrim(value) as point_string, row_number() OVER (PARTITION BY Id ORDER By Id) as Nr
    FROM Links
    CROSS APPLY STRING_SPLIT(points_string, ',')
)
, Coords AS (
    SELECT Id, Nr, CAST(value AS [varchar](max)) AS coord
    FROM Points
    CROSS APPLY STRING_SPLIT(point_string, ' ')
)
, GroupedByNr AS (
    SELECT Id, Nr, MIN(coord) AS Lon, MAX(coord) AS Lat
    FROM Coords
    GROUP BY Id, Nr
)
, GroupedById AS (
    SELECT Id, 'LINSESTRING (' + STRING_AGG(Lon + ' ' + Lat, ', ') WITHIN GROUP (ORDER BY Nr) + ')' as wkt2
    FROM GroupedByNr
    GROUP BY Id
)
SELECT Id, geography::STGeomFromText(wkt2, 4326) AS PosList2
FROM GroupedById