[Solved] How to create a Venn Diagram in OOo

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[Solved] How to create a Venn Diagram in OOo

Postby MrOffice » Tue Feb 11, 2020 3:44 pm

I want to create a coloured venn diagram. When I intersect two circular shapes the colour is not correct.

I created a red circular shape and a green one with 50 % transparency each. The intersected area has a brown colour.

How can I make the intersected area a yellow colour? Or alternatively green colour when mixing red and yellow.

Thank you.
Last edited by robleyd on Wed Feb 12, 2020 1:26 am, edited 2 times in total.
Reason: Add green tick
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Re: How to create a Venn Diagram in OOo

Postby John_Ha » Tue Feb 11, 2020 5:43 pm

It doesn't work like that.

 Edit: I used blue not green in my example 

See Merging, subtracting, or intersecting shapes in the Draw Guide where you create a blue shape, create a red shape and create an "intersection of both" shape which you colour yellow.

Clipboard03.png
Three shapes: blue, red and yellow.
Note the yellow shape has been selected.
Clipboard03.png (10.47 KiB) Viewed 225 times

1 Create both shapes
2 Create intersection shape
3 Set intersection shape to yellow
4 Copy intersection shape
5 Undo till you get the two original shapes
6 Paste the yellow intersection shape. It appears in front in exactly the correct position.

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Last edited by John_Ha on Tue Feb 11, 2020 6:01 pm, edited 2 times in total.
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Re: How to create a Venn Diagram in OOo

Postby Lupp » Tue Feb 11, 2020 5:52 pm

(Both circles assumed as "transparent 50%".)

You surely noticed that the colour shown in the area of intersection depends on the Z-order you set. Having brought to front the green circle ("green" with (R,G,B)=(0,255,0)) you don't get a lighter green or whatever colour, but something darker but still in the green range. The red circle brought to front you get a rather dark colour again, but somehow red.

Why darker? Any partial transparency leaves a partial intransparency, too. Intransparent colour will filter the colour of the background treated like "shining sun" (255,255,255) by suppressing parts of it. That's the subtractive way of combining colours.

With different words: Your expectation you would get an additive composition without any influence of te background was wrong.
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Re: How to create a Venn Diagram in OOo

Postby MrOffice » Wed Feb 12, 2020 1:07 am

you are right, haha. I thought there might be a setting to automatically set the colour space. I set it up correctly now. The solution is a combination of @John_Ha and @Lupp.

1 Create both shapes, 0 % transparency
2 Create intersection shape
3 Place intersection on top of shape
4 Set intersection area to background colour of the other shape
5 Set intersection area to 50 % transparency

this gives me a nice mixture in a subtractive colour space! For intersection with 3 areas you would use 33% transparency, of course.

thank you
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