Question

I have a mysql table containing polygons some of which are open and I need to close them. Presumably by appending the “StartPoint” to the end of the “Linestring” and rewriting as a polygon. Any ideas?

Sure I can grab out and test a polygon to see if its open or closed with

SELECT ExteriorRing(SHAPE) into @testshape from tablename where OGR_FID=1; 
SELECT (StartPoint(@testshape)) INTO @SP;
SELECT (EndPoint(@testshape)) INTO @EP;
SELECT @EP=@SP as myIsRing;

ok fine but when it’s open I need to append the Startpoint to the end of the line string in order to close the polygon. Is there a way to append that “closure” point and create a closed polygon?

Might be worth noting that I tried (as per the man page)

SELECT UNION(@testshape,@SP) INTO @newshape;

And got the standard syntax error ERROR 1064 (42000) as though my version didnt accept the UNION function.

Answer 1

Sorry everyone, Threw a couple more hours at the problem and got the following

select polygon(geomfromtext(astext(concat(geomfromtext(astext(@testshape)),(geomfromtext(astext(@SP))))))) INTO @newpoly;

Not exactly clean but it worked and can be tested with:

SELECT (StartPoint(EXTERIORRING(@newpoly))) INTO @SP2;
SELECT (EndPoint(EXTERIORRING(@newpoly))) INTO @EP2;
SELECT @EP2=@SP2 as myIsRing;