Create a legend according to the colors of a scatter plot

Hi, I have the gps coordinates (xCG and yCG) of the trajectories in a circuit of different drivers, what I would like to do is represent these colored trajectories based on the gear engaged which is saved in an NGear vector. This I did with a scatter plot like below:

scatter(xCG,yCG,10,NGear,'filled');

Now I want to create a legend like this:

legend('Gear 1','Gear 2','Gear 3','Gear 4','Gear 5','Neutral');

But clearly I would like the color in the legend to match the color in the plot. The problem is that NGear does not always contain all five gears, because for example the 5th gear is not put in one lap, this then changes from driver to driver.

So, my question is, there is a way to fix 6 colors accorting to that labels in the legend and than reproduce the same colors in the plot according to the gear engaged?

Thanks.

[dpb]

You can't do that like this -- a scatter plot is only a single plot object so there can only be one legend entry.

I think to do so you'll need to draw each scatter plot by grouping variable where the grouping variable is the gear vector.

Alternatively, you'll have to create an additional handle for each of the six gears possible and map those to the same color map range. Plotting NaN values to create invisibile handles is a common trick to be able to do such enhancements that aren't directly available.

It would help and somebody might try to solve it if you'd attach a .mat file with the data;;;otherwise folks have to try to create something and we can't really see what you actually have.

[Walter Roberson]

scatter(nan, nan) is the usual way to generate a handle for legend purposes.

[RAFFAELE MAGLIONE]

How do I plot the NaN points with the same colors of the points in the scatter plot?

[Walter Roberson]

Do you have an array that contains the "master" color for the 6 different gears? And are you ensuring that NGear is either color information appropriate for the gear actually used, or else is gear index 1 to 6, with missing gears just not present ?

[RAFFAELE MAGLIONE]

I solved it by creating a 'Color' vector which for each row contains a triple RGB based on the gear engaged, and then plots 6 NaN, one for each gear, with the color chosen for that gear, to make the legend.

Answer 1

[the cyclist]

Unless I have misunderstood your question, you should be able to do this using the gscatter command. The legend will be tied to the group (i.e. the gear), which also drives the color.

[Walter Roberson]

This sounds like a good approach for the case where the user NGear variable is a gear index, rather than being a color array directly.