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Closed Issue: using GeographyCollectionAggregate on set of points that exceed hemispehere limit raise Exception [3737]

bsdz — Thu, 16 May 2013 10:24:36 GMT

When using GeographyCollectionAggregate or GeographyUnionAggregate on set of points that exceed the hemisphere limit an Exception is raised. What would be better is if NULL is returned as this would match the behaviour of STUnion and would make the aggregate classes more usable.

For example: -

declare @x geography = 'MULTIPOINT ((0 1), (90 1), (180 1), (270 1))';
declare @y geography = 'POINT (45 1)';

select @x.STUnion(@y)

This returns NULL because by unioning @y to @x the new geography exceeds the hemisphere limit.

However if using, say GeographyCollectionAggregate, like so: -

declare @t table (
name varchar(max),
position geography
);

insert into @t (name, position) values ('object 1', 'POINT (0 1)' );
insert into @t (name, position) values ('object 1', 'POINT (90 1)' );
insert into @t (name, position) values ('object 1', 'POINT (180 1)' );
insert into @t (name, position) values ('object 1', 'POINT (270 1)' );
/* including this point causes hemisphere limit Exception */
insert into @t (name, position) values ('object 1', 'POINT (45 1)' );

select name, dbo.GeographyCollectionAggregate(position) 'locus'
from @t
group by name

The inclusion of the POINT(45 1) forces the 'locus' value to exceed the hemisphere limit but instead of returning NULL a GLArgumentException is raised.

Created Issue: Implement a method to export each geography in a resultset as a KML placemark fragment [10777]

Bigjimslade — Tue, 29 Jan 2013 05:09:12 GMT

Often when working with more than one row of data in a sql resultset, you want to return a fragment of KML, not a entire well formed kml document.

I would like to suggest that the spatial tools library implement an additional export method that just return a element as xml and optionally takes a parameter of xml to include as an node.

Commented Issue: ExportToKml should export to SqlXml [8717]

purekrome — Mon, 13 Jun 2011 04:49:43 GMT

Perhaps like so: -

[Microsoft.SqlServer.Server.SqlFunction]
public static SqlXml ExportToKml(SqlGeography g)
{
if (g == null || g.IsNull)
return new SqlXml();

MemoryStream stream = new MemoryStream();
XmlWriter writer = XmlWriter.Create(stream);

KeyholeMarkupLanguageGeography sink = new KeyholeMarkupLanguageGeography(writer);

g.Populate(sink);

sink.FinalizeKMLDocument();

writer.Flush();
stream.Seek(0, SeekOrigin.Begin);

return new SqlXml(stream);
}

Can also be added to register scripts as follows: -

create function ExportToKml(@g geography) returns xml
as external name SQLSpatialTools.[KMLFunctions].ExportToKml
go
Comments: ** Comment from web user: purekrome **

and I'm wondering if it's worth having another version of this function, which COMPRESSES (ie. zips) the output for large result sets .. so the data that goes over the wire is smaller .. at the cost of a tiny bit more cpu on both ends?

Commented Issue: ExportToKml should export to SqlXml [8717]

purekrome — Mon, 13 Jun 2011 04:33:12 GMT

Is there a performance difference with returning this as a SqlXml instead of a SqlString?

Created Issue: ExportToKml should export to SqlXml [8717]

bsdz — Tue, 31 May 2011 09:45:47 GMT

Created Issue: NullReferenceException in GeographyCollectionAggregate.Merge [5399]

tintor — Fri, 12 Feb 2010 10:16:22 GMT

A .NET Framework error occurred during execution of user-defined routine or aggregate "GeographyCollectionAggregate": System.NullReferenceException: Object reference not set to an instance of an object. System.NullReferenceException: at SQLSpatialTools.GeographyCollectionAggregate.Merge(GeographyCollectionAggregate group) .

Commented Issue: using GeographyCollectionAggregate on set of points that exceed hemispehere limit raise Exception

bsdz — Fri, 26 Jun 2009 08:30:06 GMT

I can confirm the latest fixes in SVN correct this issue. Thanks :)

Commented Issue: using GeographyCollectionAggregate on set of points that exceed hemispehere limit raise Exception

bsdz — Sun, 14 Jun 2009 23:25:35 GMT

I've noticed a problem with my patch. It simply resets the collection of points whenever an exception occurs. This has the side effect of still accumulating points after an exception. The following query exhibits this: -

declare @t table (
name varchar(max),
position geography
);

insert into @t (name, position) values ('object 1', 'POINT (0 1)' );
insert into @t (name, position) values ('object 1', 'POINT (90 1)' );
insert into @t (name, position) values ('object 1', 'POINT (180 1)' );
insert into @t (name, position) values ('object 1', 'POINT (270 1)' );
/* including this point causes hemisphere limit Exception */
insert into @t (name, position) values ('object 1', 'POINT (45 1)' );
/* then this point is included after being reset above */
insert into @t (name, position) values ('object 1', 'POINT (60 1)' );

insert into @t (name, position) values ('object 2', 'POINT (0 1)' );
insert into @t (name, position) values ('object 2', 'POINT (90 1)' );
insert into @t (name, position) values ('object 2', 'POINT (180 1)' );
insert into @t (name, position) values ('object 2', 'POINT (270 1)' );

select name,
dbo.GeographyCollectionAggregate(position) 'locus',
dbo.GeographyCollectionAggregate(position).STNumPoints(),
COUNT (*)
from @t
group by name

I've still to get more familiar with writing aggregate classes using the CLR so I couldn't work out how to place a holding flag on the accumulation stream instructing it to NULLify the aggregate at Terminate.

I can work around this by comparing the values STNumPoints and COUNT then filtering where needed.

Commented Issue: using GeographyCollectionAggregate on set of points that exceed hemispehere limit raise Exception

bsdz — Sun, 14 Jun 2009 22:35:04 GMT

Here is a patch that resolves the issue by wrapping the ConstructedGeography property in a try/catch block. This patch might be a bit naive in terms of performance and should be accompanied by documentation stating clearly that an aggregate of points exceeding the hemisphere limit will return as an empty geography collection.

Created Issue: using GeographyCollectionAggregate on set of points that exceed hemispehere limit raise Exception

bsdz — Sun, 14 Jun 2009 14:38:43 GMT