Is there a limit to the size of an array accessed via OPeNDAP with ncread?

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James Potemra 2019-8-14

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https://ww2.mathworks.cn/matlabcentral/answers/476171-is-there-a-limit-to-the-size-of-an-array-accessed-via-opendap-with-ncread

评论： James Potemra 2020-5-12

I've found when trying to access a large(ish) array via OPeNDAP using Matlab and ncread, the result returns all zeros at some array size limit.

I'm trying to figure out if this is a Matlab/ncread limit or OPeNDAP issue.

I'm accessing a data set served via OPeNDAP (GrADS-DODS to be exact) via Matlab's ncread function.

If I select the entire array, which is 192 by 94 by 58676 (lon, lat, time), ncread does not throw an error but the resulting array is all zeros.
If I subset to, for example, the first 25,000 times, it works fine. I suspect there is a 2GB limit but would like confirmation. It also seems odd that there is no error, but rather a return of zeros.

For example:

% matlab R2018b 64-bit (maci64)

URL = 'http://apdrc.soest.hawaii.edu:80/dods/public_data/Reanalysis_Data/NCEP/NCEP2/6_hourly/gaussian_grid/uwnd_10m';

lat = ncread(URL,'lat');

lon = ncread(URL,'lon');

% this returns valid data

uwind = ncread(URL,'uwnd_10m',[1 1 1],[Inf Inf 29746]);

% this returns all zeros

uwind = ncread(URL,'uwnd_10m',[1 1 1],[Inf Inf 29747]);

% as does this (note there are 192x94x58676 values)

uwind = ncread(URL,'uwnd_10m');

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G. M. Wolfe 2020-5-12

I am encountering the same problem with a different file, and the variable size is signficantly smaller (1800 * 3600, ~51 MB). I can read in the first half or second half by themselves, but it returns all 0s when I try to read the whole variable.

Please help, this is very frustrating.

James Potemra 2020-5-12

@GW, just an FYI I posted a similar question to stackoverflow (https://stackoverflow.com/questions/57487174/array-size-limit-for-matlab-ncread) with no responses.

Meanwhile, discovered that netcdf libs have a limit that can be set, but I'm not sure how/if this impacts matlab (libnetcdf has a time-out setting for http requests).

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