Question with interp3

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Trung Ngo
Trung Ngo el 31 de Mayo de 2019
Respondida: meghannmarie el 6 de Jun. de 2019
Hi all,
I got an error using interp3 as:
% Error using griddedInterpolant
% The grid vectors do not define a grid of points that match the given values.
My code is as:
addpath('nctoolbox-1.1.3');
load('matlab.mat')
setup_nctoolbox;
grib = ncgeodataset('2018_Jan.grib');
grib.variables;
grib.size('10_metre_U_wind_component_surface');
U_wind1 = grib.geovariable('10_metre_U_wind_component_surface');
grib.dimensions('10_metre_U_wind_component_surface');
size(U_wind1);
class(U_wind1);
U_wind = U_wind1.data(:, :, :);
U_wind = permute(U_wind,[2 3 1]);
U_wind = squeeze(double(U_wind));
U_wind = flipud(U_wind);
skip = length(U_wind)/2;
U_wind = circshift(U_wind,[0,skip]);
coords_latitude = -90:0.75:90;
coords_longitude = -180:0.75:179.25;
coords_lat = coords_latitude';
coords_lon = coords_longitude';
path_time_total_grib = path_time_total/6;
for i=1:size(path_lat_value,1)
for j=1:size(path_lat_value,2)
U_wind_route(i,j) = interp3(coords_lon,coords_lat,...
coords_time,U_wind,path_lon_value(i,j),path_lat_value(i,j),path_time_total_grib(i,j));
end
end
I also attach the path_lon_value, path_lat_value, path_time_total as matlab.mat and Grib file as this google drive link https://drive.google.com/open?id=1ifuEnEnSThdhsq6FHbUXDfy-DyhhB_Ba
Thank you for your help

Respuesta aceptada

meghannmarie
meghannmarie el 1 de Jun. de 2019
First error I saw was you were using lat/lon vectors that were 0.75 degree resolution where the wind data was 1 degree resolution. I instead read the lat/lon from the file to make sure the data matched the coordinates.
Next, the data's longitude range was 0:360 where the path longitude rage was -180:180. So I did the modulus of the longitude path data by 360 to fix that.
Lastly, you do not want to loop through data. Just do interp3 on complete dataset, much faster.
Try this:
addpath('nctoolbox-1.1.3');
load('matlab.mat')
setup_nctoolbox;
grib = ncgeodataset('2018_Jan.grib');
U_wind1 = grib.geovariable('10_metre_U_wind_component_surface');
U_wind = U_wind1.data(:, :, :);
U_wind = permute(U_wind,[2 3 1]);
time = grib.geovariable('time');
grib_time = double(time.data(:));
lat = grib.geovariable('lat');
grib_lat = double(lat.data(:));
lon = grib.geovariable('lon');
grib_lon = double(lon.data(:));
path_time_total_grib = path_time_total/6;
path_lon_value_grib = mod(path_lon_value,360);
U_wind_route = interp3( grib_lon,grib_lat,grib_time, U_wind,...
path_lon_value_grib,path_lat_value,path_time_total_grib);
  10 comentarios
meghannmarie
meghannmarie el 6 de Jun. de 2019
That should be correct.
I didnt have the data to see that longitude is the second dimension. So use 2 as your first input into cat because you are concatonating along the second dimension, use U_wind as second because you are adding data to end of longitudes, and U_wind(:,1,:) as the third input because that is the 1st values for longitude (0°) which is same as 360°.
U_wind_0_360 = cat(2,U_wind,U_wind(:,1,:));
Trung Ngo
Trung Ngo el 6 de Jun. de 2019
Thank you so much for your help !!!

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meghannmarie
meghannmarie el 6 de Jun. de 2019
Your welcome!

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