Problem when wrapping longitude dataset

2015 5 13
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更新时间：2015 5 14
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Hello,
I have a global dataset that I would like to wrap. I want to change its longitude from [0 360] to [-180 180]. I can successfully wrapTo180 the longitude vector, but when I plot my data, there are lines sporadically across the map. There must be something wrong with the data that is making it do this.
Please help!!
I have attached my data so you can give it a whirl
Thanks,
Melissa

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Chad Greene
Chad Greene 2015-5-13

0 个投票

Does this work?
load lat
load lon
load data
[lon,lat] = meshgrid(wrapTo180(lon_model),lat_model);
worldmap('world')
pcolorm(lat,lon,double(first_model'))
And formatting with the help of rgb, borders, and brewermap,
setm(gca,'ffacecolor',rgb('ocean blue'))
borders('countries','k')
colormap(brewermap(1024,'OrRd'))

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Melissa
Melissa 2015-5-13
编辑：Melissa 2015-5-13
This looks good! Except I would like to plot it using pcolor instead of worldmap, so it stays consistent with my other datasets. Is there a way to get this kind of output using that?
Thanks
Chad Greene
Chad Greene 2015-5-13
编辑：Chad Greene 2015-5-13
Strange! I see the striping you are referring to. Here's a manual workaround that also takes care of the vertical stripe of missing data at the prime meridian:
load lat
load lon
load data
lon = wrapTo180(lon_model);
[lon,lat] = meshgrid(linspace(min(lon),max(lon),length(lon)),...
linspace(-90,90,192));
fm = double(first_model');
fm = fm(:,[145:end 1:144]);
% Not sure if you want to do this masking:
greenland = landmask(lat,lon,'greenland');
antarctica = landmask(lat,lon,'antarctica');
fm(greenland) = 0;
fm(antarctica) = 0;
figure
pcolor(lon,lat,fm)
shading interp
set(gca,'color',rgb('ocean blue'))
borders('countries','k','nomap')
colormap(brewermap(1024,'OrRd'))
axis([-180 180 -82 86])
Chad Greene
Chad Greene 2015-5-13
...and in case you're wondering I used landmask for to turn data for Greenland and Antarctica into zeros.
Melissa
Melissa 2015-5-14
This works perfectly! Thank you so much.
However, if I wanted to keep the white vertical line there, how would I do that while keeping the rest of the blue lines out?
Chad Greene
Chad Greene 2015-5-14
I'm not sure why you want to keep that vertical line--it's an artifact of pcolor, which deletes a row and column of data. Before shifting fm with fm = fm(:,[145:end 1:144]);, pcolor would ignore the right-hand column of data, which was the column of data corresponding to the prime meridian. After the shift, pcolor discards the right-hand column of data east of New Zealand. If you want to arbitrarily discard a vertical line of data at the prime meridian, you can do so by
fm(:,144)=NaN;
which gives
Chad Greene
Chad Greene 2015-5-14
Or if you don't want to get rid of any data, you can use imagesc instead of pcolor:
load lat
load lon
load data
fm = double(first_model');
fm = fm(:,[145:end 1:144]);
% Linear arrays of lat and lon:
lon = wrapTo180(lon_model);
lon = linspace(min(lon),max(lon),length(lon));
lat = linspace(-90,90,192);
% gridded lat/lon:
[long,latg] = meshgrid(lon,lat);
% landmask takes ~30 seconds:
land = landmask(latg,long);
% Set land NaNs to zero:
fm(land & isnan(fm)) = 0;
% Set ocean to -1:
fm(isnan(fm))=-1;
imagesc(lon,lat,fm);
axis xy
set(gca,'color',rgb('ocean blue'))
borders('countries','k','nomap')
bm = brewermap(1024,'OrRd');
colormap([rgb('ocean blue');bm])
axis([-180 180 -60 86])

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