[postgis-tickets] [PostGIS] #3742: mvt regress failure on debbie and winnie

[PostGIS]

#3742: mvt regress failure on debbie and winnie
----------------------+----------------------------
  Reporter:  robe     |      Owner:  Björn Harrtell
      Type:  defect   |     Status:  assigned
  Priority:  blocker  |  Milestone:  PostGIS 2.4.0
 Component:  postgis  |    Version:  trunk
Resolution:           |   Keywords:
----------------------+----------------------------

Comment (by Björn Harrtell):

 Thanks for investigating, very valuable as I still haven't mustered up the
 guts to make a move on Debbie (or Winnie, I'm not that picky).

 Decoding the output vector tile and compare the expected to the failing in
 detail will perhaps give some more info. As of yet I've only done naive
 inspection of decoded vector tiles using vector-tile-js but I've just
 found a more detailed way to inspect using protoc-c --decode.

 The failing test case is:
 {{{
 SELECT 'TA8', encode(ST_AsMVT('test', 4096, 'geom', q), 'base64') FROM (
     SELECT 1 AS c1, ST_AsMVTGeom(ST_GeomFromText('POINT(25 17)'),
     ST_MakeBox2D(ST_Point(0, 0), ST_Point(4096, 4096)), 4096, 0, false) AS
 geom
     UNION
     SELECT 1 AS c1, ST_AsMVTGeom(ST_GeomFromText('POINT(26 18)'),
     ST_MakeBox2D(ST_Point(0, 0), ST_Point(4096, 4096)), 4096, 0, false) AS
 geom
     UNION
     SELECT 2 AS c1, ST_AsMVTGeom(ST_GeomFromText('POINT(26 18)'),
     ST_MakeBox2D(ST_Point(0, 0), ST_Point(4096, 4096)), 4096, 0, false) AS
 geom) AS q;
 }}}

 It creates a tile with three point features. Duplicate values for c1
 should only be encoded once and reused.

 Decode of the expected binary:
 {{{
 layers {
   name: "test"
   features {
     tags: 0
     tags: 0
     type: POINT
     geometry: 9
     geometry: 50
     geometry: 8158
   }
   features {
     tags: 0
     tags: 1
     type: POINT
     geometry: 9
     geometry: 52
     geometry: 8156
   }
   features {
     tags: 0
     tags: 2
     type: POINT
     geometry: 9
     geometry: 52
     geometry: 8156
   }
   keys: "c1"
   values {
     uint_value: 1
   }
   values {
     uint_value: 1
   }
   values {
     uint_value: 2
   }
   extent: 4096
   version: 2
 }
 }}}

 Decode of the unexpected binary:
 {{{
 layers {
   name: "test"
   features {
     tags: 0
     tags: 0
     type: POINT
     geometry: 9
     geometry: 50
     geometry: 8158
   }
   features {
     tags: 0
     tags: 0
     type: POINT
     geometry: 9
     geometry: 52
     geometry: 8156
   }
   features {
     tags: 0
     tags: 1
     type: POINT
     geometry: 9
     geometry: 52
     geometry: 8156
   }
   keys: "c1"
   values {
     uint_value: 1
   }
   values {
     uint_value: 2
   }
   extent: 4096
   version: 2
 }
 }}}

 On first glance it seems that the expected output is incorrectly
 containing redundant encoding of the c1 value. Both are valid tiles but
 the unexpected encode is more correct. I think I might have a lead on the
 problem here. I fixed it for string values recently but it appears I have
 similar issues with numeric values. Will look for a solution when time
 permits.

--
Ticket URL: <https://trac.osgeo.org/postgis/ticket/3742#comment:9>
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