ArcInfo ASCII Grid File Format

ArcInfo ASCII Grid refers to a specifc interchange format developed for ARC/INFO rasters in ASCII format. The format consists of a header that specifies the geographic domain and resolution, followed by the actual grid cell values.

ncols 157
nrows 171
xllcorner -156.08749650000
yllcorner 18.870890200000
cellsize 0.00833300
0 0 1 1 1 2 3 3 5 6 8 9 12 14 18 21 25 30 35 41 47 53
59 66 73 79 86 92 97 102 106 109 112 113 113 113 111 109 106
103 98 94 89 83 78 72 67 61 56 51 46 41 37 32 29 25 22 19
etc...

ncols
ncols refers to the number of columns in the grid and xxxxx is the numerical value

nrows
nrows refers to the number of rows in the grid and xxxxx is the numerical value

xllcorner
xllcorner refers to the western edge of the grid and xxxxx is the numerical value

yllcorner
yllcorner refers to the southern edge of the grid and xxxxx is the numerical value

cellsize
cellsize refers to the resolution of the grid and xxxxx is the numerical value

nodata_value
nodata_value refers to the value that represents missing data and xxxxx is the numerical value. This is optional and your parser should not assume it will be present. Note: that if you need a good value, the ESRI default is -9999.

Data values
These are the value of individual cell typically representing elevation of a particular area.

NOTES:
Although ESRI applications may accept other file extensions the file extension must be “asc” when used in GeoScene3D.

When used in GeoScene3D the decimal separator in floating point values may be either “.” or “,”. However, the file loads a lot faster when dot (“.”) separated.

xllcorner and yllcorner are given as the EDGES of the grid, NOT the centers of the edge cells.