odc compare to support a tolerance threshold?

[matthewrmshin]

Is your feature request related to a problem? Please describe.

In a recent usage of odc compare to compare a reference file to a test output, I got file differ exception when two files differs by a tiny value in a column. While the exception is correct, the difference between the values is so small that the error message does not actually tell what it is:

000 2024-08-28 11:55:03 (I) Comparator::compare: (1) ref.odb to (2) out.odb
000 2024-08-28 11:55:08 (E) Exception: Values different in column obsbias: 0.00219108 is not equal 0.00219108
000 2024-08-28 11:55:08 (E)  
000 2024-08-28 11:55:08 (I) While comparing rows number 3953389, columns 36 found different.
000 2024-08-28 11:55:08 (I)  Values different in column obsbias: 0.00219108 is not equal 0.00219108

000 2024-08-28 11:55:08 (I)  data1[36] = 2.191084e-03
000 2024-08-28 11:55:08 (I)  data2[36] = 2.191084e-03
000 2024-08-28 11:55:08 (I)  md1[36] = name: obsbias, type: REAL, codec: short_real2, range=<-1003.738464,5.535852>, hasMissing=false
000 2024-08-28 11:55:08 (I)  md2[36] = name: obsbias, type: REAL, codec: short_real2, range=<-1003.738464,5.535852>, hasMissing=false
000 2024-08-28 11:55:08 (E) Exception: Files differ.  
000 2024-08-28 11:55:08 (I) Comparing files ref.odb and out.odb: 4 seconds elapsed, 4 seconds cpu
000 2024-08-28 11:55:08 (E) ** Files differ.  Caught in  (/home/matt/opt/eckit/src/eckit/runtime/Tool.cc +32 start)
000 2024-08-28 11:55:08 (E) ** Exception terminates odc

Using odc sql to print out the columns in the files, I got this diff:

--- ref.odb.sql	2024-08-28 13:43:19.000000000 +0000
+++ out.odb.sql	2024-08-28 13:47:35.000000000 +0000
@@ -3953387,7 +3953387,7 @@
 -0.21317523717880249
 -0.44805592298507690
 0.08006642758846283
-0.00219108420424163
+0.00219108397141099
 0.04074956104159355
 0.09717535227537155
 0.29601469635963440

Describe the solution you'd like

It would be desirable for odc compare to support a tolerance threshold that can be specified by the user, so negligible differences can be ignored and for odc compare to return a success (0). For example, this will be useful for comparing reference outputs and test outputs in CI tests on alternate platforms.

Describe alternatives you've considered

Otherwise, odc compare should print a better error message that prints the full significant figures.

Additional context

No response

Organisation

Met Office