[gdal-dev] Extra Decimal places added to ASCII gdal_translate mosaic

[Norman Vine]

hmm 

this seems to be related to this fairly recent change
http://trac.osgeo.org/gdal/ticket/3732
http://osgeo-org.1560.x6.nabble.com/gdal-dev-Change-of-DECIMAL-PRECISION-in-AAIGrid-td5075524.html

don't know much more

Norman

On Jan 24, 2014, at 11:12 AM, Jonathan Moules <jonathanmoules at warwickshire.gov.uk> wrote:

> Thanks Norman. I'd already seen that page but failed to read it!
> However, having tested it, it's not functioning as the manual says.
> 
> As best I can tell, DECIMAL_PRECISION=3 should give me 3 decimal places. But what it instead does it give me 3 significant figures. So 98.354 has become 98.3.
> This becomes a problem because many of my heights are hovering around 100. So some will either have to be 1 character too long to ensure no data loss for the rest.
> 
> Is this a bug? The documentation on the page linked to is quite clear it should be decimal places.
> 
> Less of an issue, but it also didn't make any difference to:
> xllcorner    432000.000000000000
> yllcorner    242000.000000000000
> cellsize     2.000000000000
> 
> GDAL 1.10.1, released 2013/08/26
> 
> 
> Cheers,
> Jonathan
> 
> 
> 
> On 24 January 2014 15:11, Norman Vine <nhv at cape.com> wrote:
> try
>> gdal_translate -of AAIGrid -co DECIMAL_PRECISION=3  abc.vrt abc.asc
> see http://www.gdal.org/frmt_various.html
> HTH
> Norman
> 
> On Jan 24, 2014, at 10:01 AM, Jonathan Moules <jonathanmoules at warwickshire.gov.uk> wrote:
> 
>> Hi List,
>> I'm trying to mosaic some ASCII grid tiles into a single large ASCII file (which can then easily be handled).
>> 
>> I'm using this process:
>> REM Create list of files
>> dir /b /s *.asc > asc_list.txt
>>  
>> REM Turn into VRT
>> gdalbuildvrt -srcnodata "-9999" -vrtnodata "0" -a_srs "EPSG:27700" -input_file_list "asc_list.txt" abc.vrt
>>  
>> REM actual mosaicing
>> gdal_translate -of AAIGrid abc.vrt abc.asc
>> 
>> The input files are like:
>> ncols         500
>> nrows         500
>> xllcorner     432000.000
>> yllcorner     243000.000
>> cellsize      2
>> nodata_value  -9999.0
>> 98.354 98.449 98.658 98.874 99.038 99.096
>> 
>> But the outputs are like:
>> 
>> fncols        500
>> nrows        1000
>> xllcorner    432000.000000000000
>> yllcorner    242000.000000000000
>> cellsize     2.000000000000
>> NODATA_value  0
>>  98.353996276855469 98.448997497558594 98.657997131347656 98.874000549316406 
>> 
>> Suddenly everything has a dozen extra decimal places. Not only does this induce the False Precision problem (we don't have heights to the femtometer!), it also massively increases the filesize.
>> 
>> How can I get this to not happen?
>> 
>> Thanks,
>> Jonathan
>> 
>> 
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