Re: GMT 5 default format

Dear Lester,

One option is to use
gmt set IO_NC4_CHUNK_SIZE classic

But I also want to urge you to either update the tools you use, or if no update is available to urge the makers of those tools to finally update to link against the netCDF 4 library.

NetCDF 4 was introduced already some FIVE years ago and is now at version 4.3.1.1. To hold off on the very useful functionalities of the netCDF 4 library (particularly internal compression) would be like trying to move the clock many years back.

Remko

On 6 Feb 2014, at 08:04, Lester Anderson <[email protected]> wrote:

> Hello,
> 
> I have spotted a slight difference in the default grid formats from v4 to v5 and this appears to give some issues loading into other applications:
> 
> VERSION 5
> black1_emag2b_RTP.grd: Title: Anomaly reducted to the pole
> black1_emag2b_RTP.grd: Command: grdredpol black1_emag2a.grd -Gblack1_emag2b.grd -T2013 -W1 -F45/45 -V
> black1_emag2b_RTP.grd: Remark:
> black1_emag2b_RTP.grd: Gridline node registration used [Geographic grid]
> black1_emag2b_RTP.grd: Grid file format: nf = GMT netCDF format (32-bit float),COARDS, CF-1.5
> black1_emag2b_RTP.grd: x_min: 20 x_max: 50 x_inc: 0.0333333333333 name: longitude [degrees_east] nx: 901
> black1_emag2b_RTP.grd: y_min: 35 y_max: 50 y_inc: 0.0333333333333 name: latitude [degrees_north] ny: 451
> black1_emag2b_RTP.grd: z_min: -1385.10412598 z_max: 3309.81860352 name: nT
> black1_emag2b_RTP.grd: scale_factor: 1 add_offset: 0
> black1_emag2b_RTP.grd: format: netCDF-4 chunk_size: 129,151 shuffle: on deflation_level: 3 <------
> 
> VERSION 4
> black1_emag2b_RTP_v2.grd: Title: Grid computed inside Mirone
> black1_emag2b_RTP_v2.grd: Command:
> black1_emag2b_RTP_v2.grd: Remark: File written from Matlab
> black1_emag2b_RTP_v2.grd: Gridline node registration used [Geographic grid]
> black1_emag2b_RTP_v2.grd: Grid file format: nf = GMT netCDF format (32-bit float), COARDS, CF-1.5
> black1_emag2b_RTP_v2.grd: x_min: 20 x_max: 50 x_inc: 0.0333333333333 name: longitude [degrees_east] nx: 901
> black1_emag2b_RTP_v2.grd: y_min: 35 y_max: 50 y_inc: 0.0333333333333 name: latitude [degrees_north] ny: 451
> black1_emag2b_RTP_v2.grd: z_min: -1385.10412598 z_max: 3309.81860352 name: z [unknown]
> black1_emag2b_RTP_v2.grd: scale_factor: 1 add_offset: 0
> black1_emag2b_RTP_v2.grd: format: classic <------
> 
> The format reference from the headers are different. With version 4 there are no issues loading GMT (netCDF) grids into other applications like MagPick or QGIS (1.8 to 2.1), but with version 5 they are considered an unknown format, yet still the default format (=nf). 
> 
> From gmtdefaults:
> 
> # I/O Parameters
> #
> IO_COL_SEPARATOR                = tab
> IO_GRIDFILE_FORMAT              = nf
> IO_GRIDFILE_SHORTHAND           = false
> IO_HEADER                       = false
> IO_N_HEADER_RECS                = 0
> IO_NAN_RECORDS                  = pass
> IO_NC4_CHUNK_SIZE               = auto
> IO_NC4_DEFLATION_LEVEL          = 3
> IO_LONLAT_TOGGLE                = false
> IO_SEGMENT_MARKER               = >
> #
> 
> Should any parameters above be tweaked?
> 
> It is not a big issue as it is easy to change to a format that works in other applications, but it is worth noting that the subtle change in the format seems to have a big impact, given that everything else is identical. In terms of formats, what constitutes the "classic" format in the list under grdreformat?
> 
> Cheers
> Lester
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