gdalinfo on Surfer Grids is off by half grid cell

[jluis]

The info on grid size provided by gdalinfo on Surfer grids is wrong by half a grid cell. Example, generate one of such grids with GMT

grdmath -R0/10/1/14 -I1 = lixo.grd=sf

Run grdinfo 
grdinfo lixo.grd
lixo.grd: Title: Grid originally in Surfer 6 format
lixo.grd: Command:
lixo.grd: Remark:
lixo.grd: Gridline node registration used
lixo.grd: Grid file format: sf (# 6) Golden Software Surfer format 6 (float)

lixo.grd: x_min: 0 x_max: 10 x_inc: 1 name: x nx: 11
lixo.grd: y_min: 1 y_max: 14 y_inc: 1 name: y ny: 14
lixo.grd: z_min: 0 z_max: 0 name: z
lixo.grd: scale_factor: 1 add_offset: 0

Now run gdalinfo

C:\>gdalinfo lixo.grd
Driver: GSBG/Golden Software Binary Grid (.grd)
Files: lixo.grd
Size is 11, 14
Coordinate System is `'
Origin = (-0.500000000000000,14.500000000000000)
Pixel Size = (1.000000000000000,-1.000000000000000)
Corner Coordinates:
Upper Left  (  -0.5000000,  14.5000000)
Lower Left  (  -0.5000000,   0.5000000)
Upper Right (  10.5000000,  14.5000000)
Lower Right (  10.5000000,   0.5000000)
Center      (   5.0000000,   7.5000000)
Band 1 Block=11x1 Type=Float32, ColorInterp=Undefined
  Min=0.000 Max=0.000
  NoData Value=1.701410009187828e+038

The problem is that SURFER grids do not even have the concept of Pixel-is-area or pixel-registration, so the grid limits must always be given using the Pixel-is-point or grid node registration model.

Joaquim Luis

[warmerdam]

Joaquim,

GDAL always reports bounds in terms of a pixel-as-area model. It seems to me that GDAL is properly adjusting the origin by half a pixel as is required to convert from the pixel-as-point model of the grid to the model in GDAL.

So far I don't see any problem.

[jluis]

Replying to warmerdam:

Joaquim,

GDAL always reports bounds in terms of a pixel-as-area model. It seems to me that GDAL is properly adjusting the origin by half a pixel as is required to convert from the pixel-as-point model of the grid to the model in GDAL.

So far I don't see any problem.

Frank,

I guess the disagreement is exactly that. In my view the information should be faithful to what's in the file. And what is in there is x_min = 0, x_max = 10, ... For example, this thing started when I asked in Mirone the grid limits, and the info that came back to me was sinmply not correct. Since I'm interfacing with other code I thought the error was in my code. It turned out that it wasn't.

Joaquim

[warmerdam]

I'm afraid GDAL has to be true to it's own data model or else chaos would ensue.

I'm closing this on the assumption there is no problem with the driver. If you find it is wrong please reopen and further substantiate.