[ncl-talk] help reading ascii

[john koudelka]

Rick,

Thank you, that makes total sense now. I had tried flipping both lat
and lon, which was why things were still goofy. It makes perfect sense
now that I just needed to flip lat. I am getting the expected value
now.


john



On Wed, Aug 13, 2014 at 9:26 AM, Rick Brownrigg <brownrig at ucar.edu> wrote:
> Hi John,
>
> I think your latitude dimension might indeed be flipped.  The header gives
> the lon/lat for the lower-left corner, but the first row in the file --
> which will be the zero-ith row in NCL -- is the northern-most row of the
> raster:
>
> http://webhelp.esri.com/arcgisdesktop/9.3/index.cfm?TopicName=ESRI%20ASCII%20Raster%20format
>
> Hope that helps...
> Rick
>
>
> On Tue, Aug 12, 2014 at 5:31 PM, john koudelka <john.koudelka at gmail.com>
> wrote:
>>
>> I need help sorting out reading in an ArcGIS ascii raster file. The
>> values I pull for lat/lon locations don't match up with the values I
>> am showing in ArcGIS.
>>
>> The result of line 8 below should be 22.47, which is the value I get
>> in ArcGIS for this Lat/Lon. It's not a matter of a slight shift due to
>> the center of the pixel, since the values surrounding 22.47 range from
>> 21-23. I'm thinking that something's flipped in the way the ascii file
>> is read. Can someone shed some light on this for me? Hopefully this is
>> an easy answer that I'm missing. I wasn't able to figure this out
>> searching the ncl-talk archives or reading the reference manual.
>> Apologies if I did miss something glaring there.
>>
>>
>> Here is the header of the ascii file:
>> ncols 481
>> nrows 481
>> xllcorner -114.004167
>> yllcorner 38.995833
>> cellsize 0.008333
>>
>> Here is my code:
>>
>> ncl 0> load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/contributed.ncl"
>> ncl 1> tempgrid=readAsciiTable("otgrid_20091001120000.asc",481,"float",5)
>> ncl 2> tempgrid!0="lat"
>> ncl 3> tempgrid!1="lon"
>> ncl 4> endLat=38.995833+(0.008333*481)
>> ncl 5> endLon=-114.004167+(0.008333*481)
>> ncl 6> lat=fspan(38.995833,endLat,481)
>> ncl 7> lon=fspan(-114.004167,endLon,481)
>> ncl 8> tempgrid&lat=lat
>> ncl 9> tempgrid&lon=lon
>> ncl 10> print(tempgrid({41.713438},{-111.71767}))
>>
>> Variable: tempgrid (subsection)
>> Type: float
>> Total Size: 4 bytes
>>             1 values
>> Number of Dimensions: 1
>> Dimensions and sizes:   [1]
>> Coordinates:
>> Number Of Attributes: 3
>>   lon : -111.7162
>>   lat : 41.7097
>>   _FillValue :  9.96921e+36
>> (0)     25.88
>> ncl 11> print(lat(1)-lat(0))
>> (0)     0.008350372
>> ncl 12> print(lon(1)-lon(0))
>> (0)     0.008346558
>> ncl 13> print(41.713438-41.7097)
>> (0)     0.003734589
>> ncl 14> print(-111.7167-(-111.7162))
>> (0)     -0.0004959106
>> ncl 15> print(tempgrid({41.704:41.722},{-111.726:-111.708}))
>>
>> Variable: tempgrid (subsection)
>> Type: float
>> Total Size: 16 bytes
>>             4 values
>> Number of Dimensions: 2
>> Dimensions and sizes:   [lat | 2] x [lon | 2]
>> Coordinates:
>>             lat: [41.7097..41.71805]
>>             lon: [-111.7245..-111.7162]
>> Number Of Attributes: 1
>>   _FillValue :  9.96921e+36
>> (0,0)   26.64
>> (0,1)   25.88
>> (1,0)   26.28
>> (1,1)   25.98
>> ncl 16>
>>
>>
>> Thanks,
>> john
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>