Author Topic: very short process arrows  (Read 1208 times)

Offline ltjudd

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very short process arrows
« on: October 25, 2020, 09:30 AM »
Hi,

When I try and make a very short process arrow , e-sankey always seems to get confused and tries to double the arrow back- see attached file, what am I doing wrong?

regards

Lloyd

Offline pbeilschmidt

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Re: very short process arrows
« Reply #1 on: October 27, 2020, 03:49 PM »
Hello Lloyd,

great question, and I am sure it is of interest to many users. That's why I am answering in some more detail.
I also redid your little example to show 3 or 4 steps, what the issue is and how to get it fixed.

Nothing *you* are doing wrong here... just a general issue when drawing a Sankey arrow between two nodes that are located close to each other and have little spacing. In my example I left the grid on, so you can see the spacing is just one grid step (48 px).

In the first image the arrow from node "waste heat boiler" to "stack losses". I guess this arrow is later supposed to carry the difference of the waste heat input (dark red arrow from the bottom) minus the energy recovered (light red arrow to the right), so basically the losses.

The screengrab 2a shows what happens, when the arrow is drawn. A graphical artifact is produced, with "wings" protruding to the bottom and the top over the nodes. To understand why this happens, I have moved the "stack losses" node a little bit to the right, just temporarily (see 2b).

Explanation: Each Sankey arrow has two yellow waypoints. They mark the first segment of an arrow from the edge of the node where the arrow still runs vertically before it "allowed to" bend. The same is true at the destination (target node): the yellow waypoint is where the arrow comes in and then runs to the node vertically [the same principle applies for horizontal arrow connections at the node].

As you can see the yellow arrows are too far away from the nodes. The yellow arrow delimiting the first arrow segment has been moved away too far up from the node "waste heat boiler", the yellow point that marks the last vertical segment of the arrow before it connects to the node "stack losses" is too far down.
Actually they are so far away from their nodes, that they have intersected (crossed each other on the arrow line and switched sides). And this is just impossible to draw correctly.... hence the "wing artifacts".

So, how to solve this? What I did is to pull the yellow arrows closer to their respective neighboring node. In the last image (No 3) they are just a few pixels away from the node. The arrow can now run straight from start node over first and second yellow waypoint to destination node.
An alternative option would be to space the nodes a little more and move "stack losses" further away from the other node. However, leaving more space between the nodes is not always possible.

The default segment length can be set in the Options dialog on the "Diagram" page in the "Arrow" panel. You can try and set "Default Segment Length" from 40 px to - let's say - 10 px and see if that works better for you. Note that a change of the value in the options does not apply retrospectively for existing arrows, but only for the arrows being newly drawn.

This graphical issue of "very short arrows" is even worse, if you have arrow tails and arrow heads in combination with "fat" arrows. I hope this lengthy explainer can help you better manage the "very short arrows".

Peter
« Last Edit: October 27, 2020, 04:12 PM by pbeilschmidt »
Peter
e!Sankey Forum Moderator
ifu Hamburg GmbH

Offline ltjudd

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Re: very short process arrows
« Reply #2 on: December 13, 2020, 02:46 AM »
Thanks- how to get to "options dialog in arrow panel" ?
I don't have the default segment length option.

Offline pbeilschmidt

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Re: very short process arrows
« Reply #3 on: December 14, 2020, 04:21 PM »
it can be found in the Options dialog (via Menu Edit > Options) on the second page "Diagram"
Peter
e!Sankey Forum Moderator
ifu Hamburg GmbH