extract value from a multidimentional array for exact value for two dimensions

Hi everyone,

I'm a beginner in matlab and I'm facing a probably simple problem that I'm not able to solve.

I have a set of netcdf files with climate data and I need to extract values of variables for specific lon lat location.

Each files has the following information:

ncdisp(filename)

Format:

classic

Global Attributes:

Conventions = 'CF-1.6'

production = 'CNRM-RCSM4 coupled model'

nco_openmp_thread_number = 1

NCO = '"4.5.5"'

institution = 'CNRM(Centre National de Recherches Meteorologiques),Meteo-France,Toulouse'

contact = '[e-mail]'

experiment_id = 'RCSM4-3.03'

frequency = 'mon'

creation_date = '2018-11-05 11:00:27'

Dimensions:

time = 120 (UNLIMITED)

y = 160

x = 394

Variables:

time

Size: 120x1

Dimensions: time

Datatype: double

Attributes:

units = 'months since 2006-01-01 00:00:00'

calendar = 'standard'

longitude

Size: 394x160

Dimensions: x,y

Datatype: single

Attributes:

standard_name = 'longitude'

units = 'degrees_east'

latitude

Size: 394x160

Dimensions: x,y

Datatype: single

Attributes:

standard_name = 'latitude'

units = 'degrees_north'

zos

Size: 394x160x120

Dimensions: x,y,time

Datatype: single

Attributes:

units = 'm'

_FillValue = 1.000000020040877e+20

cell_methods = 'time_counter: mean'

coordinates = 'longitude latitude'

standard_name = 'sea_surface_height_above_geoid'

valid_min = -1.000000020040877e+20

valid_max = 1.000000020040877e+20

missing_value = 1.000000020040877e+20

cell_method = 'time:mean'

offline_operation = 'zos=zos+0.11'

For the "zos" variable (394x160x120) I need to extract all 120 time value for given location (i.e. lon=12.48 lat= 44.64). I've tried different approaches, based on solved problems, but none of them work.

For example, with getvalue:

lat=ncread(filename,'latitude');

lon=ncread(filename,'longitude');

zos=ncread(filename,'zos');

data=getValue(12.48, 44.64, lon, lat, zos);

I have the following error:

Check for missing argument or incorrect argument data type in call to function 'getValue'.

Any suggestion?

Thanks in advance!

Answer 1

[Galga]

Solved as follow:

latq=xxxx; %my lat
lonq=xxxx; %my lon

%finding the index for my latq and lonq
ilon = round( (lonq-lonmin)/delta_lon )+1; 
ilat = round( (latq-latmin)/delta_lat)+1; 
for i=1:120 
z (:,i)= zos(ilon,ilat,i);
end

In case someone else has my same problem!

Answer 2

[Anmol Dhiman]

Hi Galga,

I understand that you want to extract all 120 time value for given location (lattitude , longitude) from zos where zos is a 3D variable having size 394x160x120.

You can use the following code

lat = ; % the latittude value
lon = ; % the longitude value

values = zos(lat,lon,:); % the values is of dimentsion [1x1x120] and we need to reshape it.

newValue = reshape(values,[1,120]); % new values contain all the time value for a given location.

If you want to use it many times consider creating a function.

Regards,

Anmol Dhiman

[Galga]

Hi Anmol,

thanks for your answer!

Unfortunately, it doesn't work, with the following error:

Index in position 1 is invalid. Array indices must be positive integers or logical values.

Error in extract_value (line 29)

values =zos(lons, lats,:);

Error in run (line 91)

evalin('caller', strcat(script, ';'));

I suppose because in lons lats it wants the index and not the value of lon lat;

I'm able to find the index of lat (or lon) corresponding to my value but I don't know how to find the index for the lon/lat position (where both lon and lat meet my condition).

For example with

latindex = find(lat = 44.64)

I find the indexes in which my lat is what I'm searching for, but I don't know which one corresponds to "my" lon.

...

[Anmol Dhiman]

Hi Gaia,

Can you share a the input file so as to solve the issue.

Anmol Dhiman

[Galga]

here it is:

https://drive.google.com/file/d/12lMHXbNlz19Int5cE1S7k2DiPCXvCdVI/view?usp=sharing

thanks

gaia

[Anmol Dhiman]

Hi Gaia,

I have checked the dataset given, The above error is coming as zos contains NaN values. Can you verify from your end.

Regards,

Anmol Dhiman

[Galga]

Thanks again for spending time on my issues...

Unfortunately, are not the NaNs the problem. Even with a "clean" variable zos (obtained simpliy substituting the NaN with 0), I obtain the same error, "Index in position 1 is invalid. Array indices must be positive integers or logical values".

So seems I need to identify the indexes corresponding to my lon lat... Any suggestion on this?

Gaia