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grid data generation

blockmedian xyz.prn -R975/1035/985/1045 -I0.5  > xyzm.prn
surface xyzm.prn -Gbudo.grd -R -I0.5 -T0
grdinfo budo.grd

kojiok% grdinfo budo.grd
budo.grd: Title: surface
budo.grd: Command: surface xyzm.prn -Gbudo.grd -R975/1035/985/1045 -I0.5 -T0
budo.grd: Remark:
budo.grd: Normal node registration used
budo.grd: grdfile format # 0
budo.grd: x_min: 975 x_max: 1035 x_inc: 0.5 units: user_x_unit nx: 121
budo.grd: y_min: 985 y_max: 1045 y_inc: 0.5 units: user_y_unit ny: 121
budo.grd: z_min: 993.287 z_max: 1001.54 units: user_z_unit
budo.grd: scale_factor: 1 add_offset: 0

surface command creates regularly spaced binary grid data from irregulary distributed
ASCII-xyz survey data.  To prevent aliasing, the xyz data are treated with bolckmedian.
-I0.5 is grid spacing by 0.5 m.  surface creates -Ggridfile.  -T0 is a tension value to adjust
 interpolation.  -Gfilename defines output grid filename.

grdinfo shows parameters of the grid file.  
Normal node registration: Z-values on intersections of grid lines. n={(xmax-xmin)/increm}+1
Pixel node registration: Z-values in the center of each grid. n={(xmax-xmin)/increm}

Z-values are correct.

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