The dimension of the input vector in the imagesc function

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sun 2020-5-1

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评论： Bjorn Gustavsson 2020-5-3

Sample data.csv

I used the sample data in the attachment and got the result of Figure 1 when using the imagesc function, but I expected the result to be Figure 2.

(Note: XData, YData, and C in the imagesc () function correspond to the first, second, and third columns in the sample data, respectively.)

I want to ask how the dimensions of the matrix should be adjusted to be similar to the result in Figure 2. Thank you.

figure1

figure 2

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Geoff Hayes 2020-5-1

So the colours we see in the second image represent the speed at that coordinate?

sun 2020-5-2

编辑：sun 2020-5-2

We can call it a similar name like velocity field.

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Answer 1

Bjorn Gustavsson 2020-5-2

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For this type of scattered data you can use scatter, something like this:

scatter(data(:,1),data(:,2),23,data(:,3),'filled')

or if you want to reinterpolate to a regular grid you can use any of griddata, TriScatteredInterp, or scatteredInterpolant.

HTH

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sun 2020-5-2

@Bjorn Gustavsson

The figure below is the result based on the code you said. I have a question whether I can adjust the color, because it seems to have only one color.

Bjorn Gustavsson 2020-5-3

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You can adjust the intensity-levels for scatterplots with

caxis([min_level max_level])

where you chose your intensity-range to display.

Sometimes it is also preferable to plot the data in log-scale, you can do that with scatter too - provided your data is positive, just change

scatter(data(:,1),data(:,2),23,data(:,3),'filled')

to

scatter(data(:,1),data(:,2),23,log10(data(:,3)),'filled')

further you might want to dots with smaller (or larger) radius, just change 23 to whatever gives the best display. Sometimes it is worthwhile to sort the points in increasing order. This makes the dots with largest value of data(:,3) to be plotted last which reduces how much they are shaded by other points. To do that use the second out-argument from sort to generate index-vectors.

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