Opened 19 years ago
Last modified 11 years ago
#796 closed defect
gdalinfo reports wrong values on GMT grid regisred grids — at Initial Version
Reported by: | Owned by: | warmerdam | |
---|---|---|---|
Priority: | normal | Milestone: | |
Component: | default | Version: | unspecified |
Severity: | normal | Keywords: | |
Cc: | Markus Neteler, Kyle Shannon |
Description
Regarding GMT grids, gdalinfo gives uncorrect results. This creates a grid with a grid step of 1 grdmath -R-15/15/-15/15 -I1 = lixo.grd Runing grdinfo tells us lixo.grd: Title: lixo.grd: Command: grdmath -R-15/15/-15/15 -I1 = lixo.grd lixo.grd: Remark: lixo.grd: Normal node registration used lixo.grd: grdfile format # 0 lixo.grd: x_min: -15 x_max: 15 x_inc: 1 units: user_x_unit nx: 31 lixo.grd: y_min: -15 y_max: 15 y_inc: 1 units: user_y_unit ny: 31 lixo.grd: z_min: 0 z_max: 0 units: user_z_unit lixo.grd: scale_factor: 1 add_offset: 0 However gdalinfo says: Driver: GMT/GMT NetCDF Grid Format Size is 31, 31 Coordinate System is `' Origin = (-15.000000,15.000000) Pixel Size = (0.96774194,-0.96774194) Corner Coordinates: Upper Left ( -15.0000000, 15.0000000) Lower Left ( -15.0000000, -15.0000000) Upper Right ( 15.0000000, 15.0000000) Lower Right ( 15.0000000, -15.0000000) Center ( 0.0000000, 0.0000000) Note how the "Pixel Size" differs from 1 But, if we generate the GMT grid this way (a "pixel registerd" grid) grdmath -R-15/15/-15/15 -I1 -F = lixo.grd than grdinfo reports lixo.grd: Title: lixo.grd: Command: grdmath -R-15/15/-15/15 -I1 -F = lixo.grd lixo.grd: Remark: lixo.grd: Pixel node registration used lixo.grd: grdfile format # 0 lixo.grd: x_min: -15 x_max: 15 x_inc: 1 units: user_x_unit nx: 30 lixo.grd: y_min: -15 y_max: 15 y_inc: 1 units: user_y_unit ny: 30 lixo.grd: z_min: 0 z_max: 0 units: user_z_unit lixo.grd: scale_factor: 1 add_offset: 0 and gdalinfo now gives the correct pixel size. Driver: GMT/GMT NetCDF Grid Format Size is 30, 30 Coordinate System is `' Origin = (-15.000000,15.000000) Pixel Size = (1.00000000,-1.00000000) Corner Coordinates: Upper Left ( -15.0000000, 15.0000000) Lower Left ( -15.0000000, -15.0000000) Upper Right ( 15.0000000, 15.0000000) Lower Right ( 15.0000000, -15.0000000) Center ( 0.0000000, 0.0000000) What seams to be happening is that gdal assumes all grids have a "pixel registration". And that is not allways true, in what ragards GMT grids, but it is also not true for example with GTOPO30 (or SRTM30) and SRTM 1-arc-sec or SRTM 3-arc-sec. The first are pixel registerd, but the seconds are grid registerd. See http://gmt.soest.hawaii.edu/gmt/doc/html/GMT_Docs/node145.html for a explanation on the difference between "grid" and "pixel" registrations.
Note:
See TracTickets
for help on using tickets.
Sample Grid with grid registered convention.