[PostGIS] #5735: ST_TRANSFORM uses Helmert transformation instead of NTV2 grid (SRID's : 3812 <->31370)

[PostGIS]

#5735: ST_TRANSFORM uses Helmert transformation instead of NTV2 grid (SRID's :
3812 <->31370)
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  Reporter:  martinvdb  |      Owner:  rouault
      Type:  defect     |     Status:  new
  Priority:  medium     |  Milestone:  PostGIS 3.4.3
 Component:  postgis    |    Version:  3.4.x
Resolution:             |   Keywords:  ST_TRANSFORM Belgium NTV2
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Comment (by martinvdb):

 @rouault

 Sorry it took me so long to reply.
 Yes of course, here is an example of the problem :
 We have our reference dataset which is :
 Coordinates in EPSG 31370 : X = 156681.404 ; Y = 238403.825
 Coordinates IS EPSG 3812  : X = 656673.068 ; Y = 738404.595

 When I use
 "ST_AsText(ST_Transform(ST_SetSRID(ST_MakePoint(156681.404,238403.825),
 31370), 3812));" I get, on postgreSQL/postGIS : POINT(656672.8903371155
 738404.4813479027)

 When I use "echo 156681.404 238403.825 | cs2cs epsg:31370 +to  epsg:3812
 -d 3 --only-best=yes"
 I get on PROJ : 656673.067      738404.595
 Proj_info returns that the best transformation is the one using the NTV2
 grid
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Ticket URL: <https://trac.osgeo.org/postgis/ticket/5735#comment:3>
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