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createOperations(): prefer simpler pipelines / affects WGS 84 to GDA94/GDA2020 #3248

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merged 1 commit into from
Jul 13, 2022

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@rouault rouault commented Jul 3, 2022

Prior to this change, transforming to WGS 84 to GDA2020 used in priority
transformation EPSG:9690 ("WGS 84 to GDA2020 (3)"), which is a Helmert
transformation assuming WGS 84 ~= GDA94.
But transforming from GDA2020 to WGS 84 used EPSG:8450 "GDA2020 to WGS
84 (2)" which is a no-op.
Both have the same advertized accuracy 3m
Similar case for WGS 84 <--> GDA94.

This non symetric behaviour is clearly non-desirable in scenarios where
data is transformed back and forth. I believe it is preferable to use in
that situation of transformations with the same accuracy to use the one
that involves the less transformation steps, ie the no-op one.

Seen when checking #2348 again
(whose bulk issues happens to have been fixed by other previous commits)

CC @nyalldawson

…4/GDA2020

Prior to this change, transforming to WGS 84 to GDA2020 used in priority
transformation EPSG:9690 ("WGS 84 to GDA2020 (3)"), which is a Helmert
transformation assuming WGS 84 ~= GDA94.
But transforming from GDA2020 to WGS 84 used EPSG:8450 "GDA2020 to WGS
84 (2)" which is a no-op.
Both have the same advertized accuracy 3m
Similar case for WGS 84 <--> GDA94.

This non symetric behaviour is clearly non-desirable in scenarios where
data is transformed back and forth. I believe it is preferable to use in
that situation of transformations with the same accuracy to use the one
that involves the less transformation steps, ie the no-op one.

Seen when checking OSGeo#2348 again
(whose bulk issues happens to have been fixed by other previous commits)
@rouault
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rouault commented Jul 12, 2022

@nyalldawson Does this change look appropriate to you ?

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@rouault

This looks safe to me. +1 to merge!

@rouault rouault merged commit 1bae784 into OSGeo:master Jul 13, 2022
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2 participants