Difference in lonlat to utm with current master

[snowman2]

cs2cs
Rel. 6.2.1, November 1st, 2019
usage: cs2cs [-dDeEfIlrstvwW [args]] [+opt[=arg] ...]
                   [+to +opt[=arg] ...] [file ...]
echo '-111.5 45.25919444444' | cs2cs '+proj=longlat +datum=WGS84' '+proj=utm +zone=10 +datum=NAD27'
1402291.08	5076289.59 0.00

Current master:

./cs2cs
Rel. 6.3.0, January 1st, 2020
usage: cs2cs [-dDeEfIlrstvwW [args]] [+opt[=arg] ...]
                   [+to +opt[=arg] ...] [file ...]
echo '-111.5 45.25919444444' | ./cs2cs '+proj=longlat +datum=WGS84' '+proj=utm +zone=10 +datum=NAD27'
1402285.98	5076292.42 0.00

Just noticed the difference and wanted to make sure it was expected. Feel free to close this issue if everything is okay.

[rouault]

If there's only the US 'conus' grid available, the master result is appropriate as it uses it. PROJ 6.2.1 used the NAD27 to WGS 84 (3) operation using a rough Helmert transformation, valid for Canada, which wasn't the best choice.
That said, with this test point, and both the US 'conus' and Canadian 'ntv2_0.gsb' grids were available, the later was tried, and as the point didn't find in any of its subgrid it resulted in an error. So #1809 adds a logic to fallback to the next best choice, so here 'conus'

[snowman2]

Thanks!

[snowman2]

Just relaying tests results with 6.3.0RC1:

$ ls ../share/proj/
alaska        GL27      nad27         nzgd2kgrid0005.gsb    stlrnc
BETA2007.gsb  hawaii    nad83         other.extra           stpaul
CH            ITRF2000  nad.lst       proj.db               TN
conus         ITRF2008  ntf_r93.gsb   projjson.schema.json  WI
egm96_15.gtx  ITRF2014  ntv1_can.dat  prvi                  WO
FL            MD        null          stgeorge              world

echo '-111.5 45.25919444444' | ./cs2cs '+proj=longlat +datum=WGS84' '+proj=utm +zone=10 +datum=NAD27'
1402285.98	5076292.42 0.00

./projinfo -s '+proj=longlat +datum=WGS84 +type=crs' -t '+proj=utm +zone=10 +datum=NAD27 +type=crs'

Operation n°1:

unknown id, axis order change (2D) + Inverse of NAD27 to WGS 84 (3) + axis order change (2D) + UTM zone 10N, 20 m, Canada - NAD27

PROJ string:
+proj=pipeline +step +proj=unitconvert +xy_in=deg +xy_out=rad +step +proj=push +v_3 +step +proj=cart +ellps=WGS84 +step +proj=helmert +x=10 +y=-158 +z=-187 +step +inv +proj=cart +ellps=clrk66 +step +proj=pop +v_3 +step +proj=utm +zone=10 +ellps=clrk66
--
Operation n°2:

unknown id, axis order change (2D) + Inverse of NAD27 to WGS 84 (79) + axis order change (2D) + UTM zone 10N, 5 m, USA - CONUS including EEZ

PROJ string:
+proj=pipeline +step +proj=unitconvert +xy_in=deg +xy_out=rad +step +inv +proj=hgridshift +grids=conus +step +proj=utm +zone=10 +ellps=clrk66
--

Then, downloading proj-datumgrid-north-america-1.3RC1.tar.gz:

echo '-111.5 45.25919444444' | ./cs2cs '+proj=longlat +datum=WGS84' '+proj=utm +zone=10 +datum=NAD27'
1402286.33	5076292.30 0.00

./projinfo -s '+proj=longlat +datum=WGS84 +type=crs' -t '+proj=utm +zone=10 +datum=NAD27 +type=crs'

Operation n°1:

unknown id, axis order change (2D) + Inverse of NAD27 to WGS 84 (33) + axis order change (2D) + UTM zone 10N, 1 m, Canada - NAD27

PROJ string:
+proj=pipeline +step +proj=unitconvert +xy_in=deg +xy_out=rad +step +inv +proj=hgridshift +grids=ntv2_0.gsb +step +proj=utm +zone=10 +ellps=clrk66
--
Operation n°2:

unknown id, axis order change (2D) + Inverse of NAD27 to WGS 84 (3) + axis order change (2D) + UTM zone 10N, 20 m, Canada - NAD27

PROJ string:
+proj=pipeline +step +proj=unitconvert +xy_in=deg +xy_out=rad +step +proj=push +v_3 +step +proj=cart +ellps=WGS84 +step +proj=helmert +x=10 +y=-158 +z=-187 +step +inv +proj=cart +ellps=clrk66 +step +proj=pop +v_3 +step +proj=utm +zone=10 +ellps=clrk66
--
Operation n°3:

unknown id, axis order change (2D) + Inverse of NAD27 to WGS 84 (79) + axis order change (2D) + UTM zone 10N, 5 m, USA - CONUS including EEZ

PROJ string:
+proj=pipeline +step +proj=unitconvert +xy_in=deg +xy_out=rad +step +inv +proj=hgridshift +grids=conus +step +proj=utm +zone=10 +ellps=clrk66