JR29300: ST_DIFFERENCE APPEARS TO MISS REMOVING A VOID IN THE MIDDLE OF A POLYGON, WHEN COVERED BY THE SECOND POLYGON.

DB2 Version 9.1 Fix Pack 7  for Linux, UNIX and Windows
DB2 Version 9.1 Fix Pack 6   for Linux, UNIX and Windows
DB2 Version 9.1 Fix Pack 6a for Linux, UNIX and Windows
DB2 Version 9.1 Fix Pack 7a  for Linux, UNIX and Windows
DB2 Version 9.1 Fix Pack 8  for Linux, UNIX and Windows
DB2 Version 9.1 Fix Pack 9  for Linux, UNIX and Windows
DB2 Version 9.1 Fix Pack 10  for Linux, UNIX and Windows
DB2 Version 9.1 Fix Pack 11  for Linux, UNIX and Windows
DB2 Version 9.1 Fix Pack 12  for Linux, UNIX and Windows

APAR status

• Closed as program error.

Error description

• This is regards to DB2 spatial extender on LUW - version 8.2
  and/or 9.1.
  The use of ST_Difference with this data is basically a square
  donut and
  is giving the wrong result.  The first polygon is the donut
  itself and
  the 2nd polygon is the 'hole' of the donut.
  
  ST_Difference appears to miss removing a void in the middle of a
  polygon, when covered by the second polygon.
  
  'polygon ((1 1, 1 3, 3 3, 3 1, 1 1), (1.5 1.5, 1.5 2.5, 2.5 2.5,
  2.5
  1.5, 1.5 1.5))'
   'polygon ((1.5 1.5, 1.5 2.5, 2.5 2.5, 2.5 1.5, 1.5 1.5))'
  
  Should return first polygon again
  
  'polygon ((1 1, 1 3, 3 3, 3 1, 1 1), (1.5 1.5, 1.5 2.5, 2.5 2.5,
  2.5
  1.5, 1.5 1.5))'
  
  Returns only the outer polygon
  
  'polygon ((1 1, 1 3, 3 3, 3 1, 1 1))?
  
  ST_Difference takes two geometries of the same dimension as
  input and
  returns that portion of the first geometry that is not
  intersected by
  the second geometry.
  
  With the case above one should return the geometry with the hole
  in it.
  

Local fix

Problem summary

• Users affected: All Spatial Extender
  
  Problem description:
  The ST_Difference spatial function returns an incorrect geometry
  in some cases.
  
  ST_Difference takes two geometries of the same dimension as
  input and returns that portion of the first geometry that is not
  intersected by the second geometry.
  
  This is an example of the failing case with a "square" donut:
  The first polygon is the donut itself and
  the 2nd polygon is the 'hole' of the donut.
  
  ST_Difference misses removing a void in the middle of a
  polygon, when covered by the second polygon.
  
  'polygon ((1 1, 1 3, 3 3, 3 1, 1 1), (1.5 1.5, 1.5 2.5, 2.5 2.5,
  2.5 1.5, 1.5 1.5))'
  'polygon ((1.5 1.5, 1.5 2.5, 2.5 2.5, 2.5 1.5, 1.5 1.5))'
  
  Should return first polygon again
  
  'polygon ((1 1, 1 3, 3 3, 3 1, 1 1), (1.5 1.5, 1.5 2.5, 2.5 2.5,
  2.5 1.5, 1.5 1.5))'
  
  Returns only the outer polygon
  'polygon ((1 1, 1 3, 3 3, 3 1, 1 1))
  

Problem conclusion

• Recommendation: upgrade to DB2 V9.1 FP6 or V9.5 FP2.
  

Temporary fix

Comments

APAR Information

• APAR is sysrouted FROM one or more of the following:

  JR29299

• APAR is sysrouted TO one or more of the following:

Fix information

• Fixed component name

  SPATIAL EXT LIN

• Fixed component ID

  5648D6103

Applicable component levels

• R910 PSY

     UP

• R950 PSY

     UP

• R970 PSY

     UP