Any idea how to recreate this plot?

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Ajmal Rasheeda Satheesh 2023-3-26

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https://ww2.mathworks.cn/matlabcentral/answers/1935509-any-idea-how-to-recreate-this-plot

评论： Adam Danz 2023-4-9

I have all the necessary data, windspeed as a function of height and time, wind direction in degrees also a function of height and time. I just cannot figure out how to plot a quiver plot on top of a pcolor plot

Any help would be great

Thanks

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Answer 1

Adam Danz 2023-3-26

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https://ww2.mathworks.cn/matlabcentral/answers/1935509-any-idea-how-to-recreate-this-plot#answer_1201299

编辑：Adam Danz 2023-4-9

在 MATLAB Online 中打开

test_var.mat

> I just cannot figure out how to plot a quiver plot on top of a pcolor plot

Plot the pcolor data and then the quiver data.

I noticed that in your image, all of the quiver arrows look like they have the same magnitude. I assume this is part of your data, otherwise you'll need to adjust the u and v values. The arrows in this demo do not have the same magnitude.

load wind

x = x(:,:,3);

y = y(:,:,3);

u = u(:,:,3);

v = v(:,:,3);

pcolor(x,y,u);

hold on

quiver(x,y,u,v, 'k-','LineWidth',1.5)

Update: rescaling with datetime

Currently quiver does not accept datetime which is why the datetime values are converted to numeric. But the numeric values are very large which causes issues with scaling quiver arrows. I noticed your timestamps only span the course of a day so there's no need to use gigantic x values.

This solution converts your datetime values to minute from midnight. You've got about 1425 minutes and your y values ranges about 2000 so the plot aspect ratio will be more reasonable.

See in-line comments for details.

% Load data

load('test_var.mat');

% Convert numeric timestamps to datetime

timestamps = datetime(T_wind_30min,'ConvertFrom','datenum');

% Shift all timestamps by the stating date

baseDate = dateshift(min(timestamps(:)),'start','day');

timestampsShift = timestamps - baseDate;

% Convert timestamps to minutes from the start of the first day in the data

timeMinutes = minutes(timestampsShift);

% Plot pcolor

f1=figure();

Y=pcolor(timeMinutes,H_wind_30min,dl_wind_out_day.dl_w_30min);

set(Y,'EdgeColor', 'none');

colormap(jet);

ylim([0 2000]);

cl=colorbar;cl=colorbar;

clim([-2,2])

% Add quiver

hold on

Q=quiver(timeMinutes, H_wind_30min, xWind_unit_30min, yWind_unit_30min, 'k-');

% Set xaxis datetime tick labels

baseDate.Format = 'HH:mm';

xt = 0 : 180 : 1400;

xtlab = string(baseDate + minutes(xt));

set(gca, 'XTick', xt, 'XTickLabel', xtlab)

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Adam Danz 2023-4-7

在 MATLAB Online 中打开

test_var.mat

I ran your code in R2022a and was able to reproduce the horizontal lines when I didn't use quiver scaling and the small arrows you described when using your quiver scaling values.

To understand why we're seeing mostly horizontal lines let's look closer at your data.

The horizontal vector components are relatively larger in magnitude than the vertical components so we can expect some amount of horizontal dominance. The plot below shows the distributions of your horizontal (top) and vertical (bottom) vector components (u,v).

More importantly, look at the aspect ratio of your data and plot. The range of x values is about 0.98 (range(xlim)) while the range of y values is 2000 (range(ylim)). That means vertical components of the vector need to be much larger than horizontal components to avoid horizontal quiver lines.

As you discovered, you need to scale down the vectors since their magnitudes are much larger than the x-axis range but they are also much smaller than the y-axis range. Since the size of the arrow head depends on the magnitude of the quiver arrow, there's not much you can do to show the arrow heads with these data. Note, there is a MaxHeadSize property but increasing that value didn't help in this case.

If that still isn't clear, let' look at just your quiver data.

load('test_var.mat');
scale = .001;
Q=quiver(T_wind_30min, H_wind_30min, xWind_unit_30min, yWind_unit_30min, scale,'k-',LineWidth=0.2);
Q.MaxHeadSize = 1;
xlabel('Small x range, large horizontal components')
ylabel('Large y range, small horizontal components')

Now let's zoom into the area circled in red.

It looks like a single flat line but if we set the axes' aspect ratio to 1:1 we can see the quiver arrows.

axis equal

Ajmal Rasheeda Satheesh 2023-4-8

I guessed the range between x and y axis was the issue too, but the thing is my axis is datetime in datenum. Is there any way to get the arrows to show up?, some kind of normalization of the horizontal wind values?