[ncl-talk] help reading ascii

[john koudelka]

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