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What is the definition of stdistance in SQL?
STDistance (geography Data Type) Returns the shortest distance between a point in a geography instance and a point in another geography instance.
When does stdistance return NULL in SQL Server?
The result is expressed in the unit of measure defined by the Spatial Reference Identifier (SRID) of spatial data. STDistance () always returns null if the spatial reference IDs (SRIDs) of the geography instances do not match.
How to calculate the distance between two instances of geography?
Methods on the geography data type that calculate an area or distance will return different results based on the SRID of the instance used in the method. For more information about SRIDs, see Spatial Reference Identifiers (SRIDs). The following example finds the distance between two geography instances.
When does stdistance ( other _ geography ) return null?
If other_geography is an empty set, STDistance () returns null. The result is expressed in the unit of measure defined by the Spatial Reference Identifier (SRID) of spatial data. STDistance () always returns null if the spatial reference IDs (SRIDs) of the geography instances do not match.
How to find a place within a distance?
3 Finding Places Within a Distance Using an Index In order to utilize indices on the Lat and Lon columns we can use a method similar to the bounding rectanglemethod in Cartesian space. Let’s call the circle that is formed by all points which have distance dfrom Mthe query circle.
How to find points within a distance of a latitude?
Although M=(lat, lon)=(1.3963 rad, -0.6981 rad) and PS=(lat, lonS)=(1.3963 rad, -1.6020 rad) have a distance of d=1000 km on the small circle, we could take a shortcut from Mto PSon a great circle. According to equation 1, that shortcut has a length of 967 km. So we could move another 33 km and would still be within the query circle.
How do you find points within a query circle?
Points outside this rectangle are therefore definitely not within distance dfrom M, so in order to find points that are within the query circle, we need to consider the points within the bounding rectangle only. Those points (called candidate places) can be found quickly using an index (see section 3.5for SQL queries).