Author Topic: Different scaling groups on one diagram  (Read 52 times)

Offline ltjudd

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Different scaling groups on one diagram
« on: May 17, 2020, 02:10 PM »
At present, when I move the scaling slider, it changes the scale of every flow process in the same proportion.
I would like to know if it is possible to have different scaling groups. Looking at  one of your example Sankey diagrams  on the front page of your site, The "EV energy cycle" - you have two loops that come together at the bottom. They look about the same size but one says 49 % and the other side says 82 %, so I am assuming it is possible to scale different parts individually.

Offline pbeilschmidt

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Re: Different scaling groups on one diagram
« Reply #1 on: May 18, 2020, 01:18 PM »
Hello ltjudd,

thanks for your post. I am posting the sample Sankey diagram you are referring to in the attach, so that the other visitors in this forum get an idea what you are talking about. For those users who have a full version at hand, or a trial version e!Sankey 5 on their computer, this sample can be found as "EV energy cycle" on the start page (you might have to click on "More Sankey diagrams" to choose it).

In this image I highlighted the two percentage values you are referencing and I also set the balance label for the node 'Kinetic Energy' at the bottom.

Your assumption that "it is possible to scale different parts individually" is correct, but not in this example.

Generally speaking, scaling different parts (i.e. flows of a Sankey diagram) individually is only possible for different unit types. If you are using flows with different unit types in one diagram (e.g. "Mass" and "Energy") then you will see two scaling sliders at the right side. Using these two sliders you can scale separately for "Mass" (e.g. 100 tons = 25 px) and "Energy" (3 kWh = 10 px).

Now, in the above-mentioned "EV energy cycle" Sankey diagram there is only one unit type and one unit (kW).

The flow arriving on the left side (input side) at the "Kinetic Energy" node has a flow quantity of 36.5235 kW, and the three flows leaving the node (output side) sum up to 36.5235 kW too. Have a look at the balance label I added for the node: input and output are balanced.

As you may have noted the whole diagram doesn't show any absolute numbers for flow values in kW. Instead it only shows percentage values. The percentage values should be interpreted as X % of the output of the previous node. So 49% of the power at the wheel is as kinetic energy (51% is lost as air drag and rolling friction). That is the label marked on the left side. Of the kinetic energy 82% is the flow going to the next node, while 18% are losses again. That is the label marked on the right side.
[Please don't ask me about the naming of the nodes, and why this next node is "Wheel" again. My guess is that the left of the "cycle" is to be interpreted as the acceleration part, while the right part is deceleration/braking and energy recovery from braking action. The Diagram should be read counter-clickwise only in my eyes.]

So the flows in the diagram are all on the same scale (power, kW) and only the percentage labels differ. The percentage labels show the fraction of the sum of outputs of the preceding node.

Hope that explanation helped.


Peter Müller-Beilschmidt
e!Sankey Forum Moderator
ifu Hamburg GmbH