I should perhaps of explained my code (included in top post) a little better,
the values in my attached file aren't on a regular grid to start with, I do
a little bit of juggling as follows to get them into a regular grid:
I'm firstly setting up my 2D grid of 0.5 degree lat lons, followed by
identically sized grids of zeros for the data bin, and mean divisors:
x = np.arange(-180, 180, 0.5); y = np.arange(-90, 90, 0.5)
grid_lon, grid_lat = np.meshgrid(x,y) #regularly spaced 2D grid
n_vals = np.zeros((360,720)) #mean divisor
dat = np.zeros((360,720)) #2D grid of zeros
I'm then taking my input data (e.g. the .plt file attached), and rounding
the lat lons to the nearest 0 or 0.5:
lon = (np.around(lon*2))/2 #round to nearest .0 or 0.5
lat = (np.around(lat*2))/2 #round to nearest .0 or 0.5
Then for each row in my input file where Z is greater than 0, I'm adding the
n'th Z value to its corresponding position in the dat zeros array, and
keeping a count of how many values are going into each cell in the mean
divisor array:
j=0
for i in slcol:
if lon[j] < 0:
grid_lon_ind = 360+(lon[j]*2)
grid_lat_ind = 180+(lat[j]*2)
else:
grid_lon_ind = 360-(lon[j]*2)
grid_lat_ind = 180+(lat[j]*2)
if i > 0:
dat[grid_lat_ind, grid_lon_ind] += i #add i'th value
n_vals[grid_lat_ind, grid_lon_ind] += 1 #increase cell counter by 1 for
each extra value
j+=1
Finally the new dat array is divided by the mean divisor array to give me my
mean Z values:
dat = np.nan_to_num(dat/n_vals)
I've done it this way as opposed to interpolating *properly* in order to
(for instance) stop the values bleeding away from the edges of the satellite
swath.
Cheers,
Will.
Jeff Whitaker wrote:
>
> On 4/5/10 4:16 AM, Will Hewson wrote:
>> Hey Jeff,
>>
>> It's somewhere between the two - the original satellite swath is
>> converted
>> to a regular 0.5 degree grid by truncating, binning, and averaging each
>> point's lons and lats over the top of a 720 x 360 np.zeros array. the
>> plotting still works fine for non ortho/ hemispherical projections, and
>> I've
>> no big problem with using global projections for the time being. Thanks
>> for
>> your help in the meantime anyway.
>>
>> Cheers,
>>
>>
>> Will.
>>
>
> Will: If it's a regular 0.5 degree lat/lon grid, it should work in
> transform_scalar. However, I don't see how to read the data in your
> test.plt file into a regular 360x720 grid. It seems to only contain the
> points in the swath with nonzero values.
>
> -Jeff
>>
>>
>> Jeff Whitaker wrote:
>>
>>> On 4/4/10 11:06 AM, Will Hewson wrote:
>>>
>>>> Hi again Jeff et al...
>>>>
>>>> I've had a play around with the extra few lines of code - on paper this
>>>> seems like it should solve the problems I'm experiencing. However, an
>>>> error's being thrown up by the transform scalar function, as my lons
>>>> and
>>>> lats won't necessarily be increasing. The data I'm plotting is
>>>> satellite
>>>> data and so at the beginning and end of the orbit file lats go over the
>>>> pole
>>>> from 90 to -90, with a similar problem for the lons - whereby the data
>>>> is
>>>> taken across the satellite track. I've thought about sorting the data
>>>> before
>>>> passing it to transform_scalar but I'm always going to be left with the
>>>> problem in either lats or lons.
>>>>
>>>> I've uploaded the file I'm currently working with this time. It's three
>>>> columns of lons, lats and z values.
>>>>
>>>> Once again, many thanks for your help.
>>>>
>>>> Will.
>>>>
>>>> http://old.nabble.com/file/p28133659/test.plt test.plt
>>>>
>>>>
>>> Will: Is it a regular lat/lon grid or a satellite swath? If it's the
>>> latter, you can't use my solution.
>>>
>>> -Jeff
>>>
>>>
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