[gdal-dev] Change of DECIMAL_PRECISION in AAIGrid

[peifer]

Casper Børgesen wrote
> This is my syntax:
> 
> gdal_translate -of AAIGrid -ot Float32 -co DECIMAL_PRECISION=2
> my_source.vrt my_target.asc
> 
> I have tried the above syntax using gdal 1.9.2 and 1.10 and these are
> examples from my results:
> 
> 1.9.2:
> ...
> 3.77 3.83 3.89 3.87 3.79 3.49 3.03 2.50 1.96 1.56 1.29 0.95 0.77 0.54 0.53
> 0.41
> ...
> 
> 1.10:
> ...
> 3.8 3.8 3.9 3.9 3.8 3.5 3 2.5 2 1.6 1.3 0.95 0.77 0.54 0.53 0.41
> ...
> 
> Has the meaning of DECIMAL_PRECISION changed from 1.9.2 to 1.10?
> 
> It seems like in 1.9.2 the meaning is X characters to the right of the
> comma and in 1.10 it means X describing characters?
> 
> I haven't tried the 1.10.1 release because I can't find the binaries on
> Tamas gisinternals.

Hmm. After a look into the source code [0] and some testing [1], it looks to
me that DECIMAL_PRECISION is used as precision of a "%.<precision>g" format. 

Format letter g means: "Print a number in either scientific notation or in
floating-point notation, whichever uses fewer characters."

For format letter g, the precision value defines: "Maximum number of
*significant* digits."

I see there has been this change recently:
http://trac.osgeo.org/gdal/changeset/25032/trunk/gdal/frmts/aaigrid/aaigriddataset.cpp 

Hermann

[0]
http://trac.osgeo.org/gdal/browser/trunk/gdal/frmts/aaigrid/aaigriddataset.cpp#L1051

[1]

# Input file

$ cat in.asc
ncols 1
nrows 4
xllcorner 1
yllcorner 1
cellsize  1
0.00012345
1.12345678
22.1234567
333.123456

# Test run

$ for i in 1 2 3 4 5 ; do 
  echo DECIMAL_PRECISION=$i &&
  gdal_translate -of AAIGrid -ot Float32 -co DECIMAL_PRECISION=$i in.asc
out.asc &&
  cat out.asc
done

# Output

DECIMAL_PRECISION=1

ncols        1
nrows        4
xllcorner    1.000000000000
yllcorner    1.000000000000
cellsize     1.000000000000
 0.0001
 1
 2e+01
 3e+02

DECIMAL_PRECISION=2

ncols        1
nrows        4
xllcorner    1.000000000000
yllcorner    1.000000000000
cellsize     1.000000000000
 0.00012
 1.1
 22
 3.3e+02

DECIMAL_PRECISION=3

ncols        1
nrows        4
xllcorner    1.000000000000
yllcorner    1.000000000000
cellsize     1.000000000000
 0.000123
 1.12
 22.1
 333

DECIMAL_PRECISION=4

ncols        1
nrows        4
xllcorner    1.000000000000
yllcorner    1.000000000000
cellsize     1.000000000000
 0.0001234
 1.123
 22.12
 333.1

DECIMAL_PRECISION=5

ncols        1
nrows        4
xllcorner    1.000000000000
yllcorner    1.000000000000
cellsize     1.000000000000
 0.00012345
 1.1235
 22.123
 333.12




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