[R-sig-Geo] Writing an ASCII grid with nodata values

[Ned Horning]

Roger,

Thanks for the note. Using:

options="DECIMAL_PRECISION=3", mvFlag=-9999

did the trick.

All the best,

Ned

Roger Bivand wrote:
> On Sat, 21 Nov 2009, Paul Hiemstra wrote:
>
>> Hi Ned,
>>
>> Is it an option to switch to another GDAL format, GTiff for example? 
>> Check if this exports the NA values correctly. Not really an answer 
>> to your question, but maybe a helpful suggestion.
>>
>> cheers and good luck,
>> Paul
>>
>> Ned Horning wrote:
>>> I am trying to export a SpatialPixelsDataFrame object with floating 
>>> point values to an ASCII grid file and want to specify a nodata 
>>> value. I tried write.asciigrid from the sp package and I couldn't 
>>> figure out how to output float values. The pixel values exported as 
>>> integers.
>>>
>>> For now I am using the following writeGDAL statement:
>>> -- 
>>> writeGDAL(sp_hsm_pard, out_pard, drivername="AAIGrid", 
>>> type="Float32", options="DECIMAL_PRECISION=3", "NODATA=-9999")
>
> Maybe reading:
>
>> args(writeGDAL)
> function (dataset, fname, drivername = "GTiff", type = "Float32",
>     mvFlag = NA, options = NULL, copy_drivername = "GTiff")
>
> would help?
>
> You are getting:
>
> dataset=sp_hsm_pard, fname=out_pard, drivername="AAIGrid", 
> type="Float32", options="DECIMAL_PRECISION=3", mvFlag="NODATA=-9999"
>
> by argument names and positions, I think, where internally 
> as.double("NODATA=-9999") is being coerced to an NA (a warning may 
> have been shown.
>
> Perhaps try setting mvFlag=-9999? If you wanted to put it in the 
> options, that may work, but as.double(mvFlag) is explicitly set as the 
> no-data value on the band(s) being written in create2GDAL() inside 
> writeGDAL().
>
> Hope this helps,
>
> Roger
>
>
>>>
>>> -- 
>>> This appears to output the image okay but it is not assigning the 
>>> proper values to NODATA_value. The NODATA_value in the exported file 
>>> is "1" instead of "-9999".
>>>
>>> Can someone let me know how to output floating point data to an ESRI 
>>> ASCII grid file and specify a nodata value.
>>>
>>> Thanks,
>>>
>>> Ned
>>>
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>>
>>
>>
>