GH and area calculation = weird

Hello,

please look at the image.

As you can see i set up a simple "label displayer", showing the area of certain polylines.

what is really puzzling me is the behaviour described in the image:

you can see a comparison between "area" command from rhino and the area calculation from grasshopper.

What is astonishing is that...sometimes GH is wrong. REALLY REALLY wrong, not just a few decimal digits.

See the first half: Rhino says: 717,5 square meters, and GH says...717 (rounded) OK.

See the second half (same file, same everything): Rhino says: 113.9, and GH says... 11.9!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

how is that possible??? this makes this method totally unreliable, because sometimes is correct and sometimes not. what is the reason of this? how can i fix it?

thanx

Replies to This Discussion

Permalink Reply by nikos tzar on July 12, 2016 at 6:21am

Hello Jay,

Can you internalize the curve that gives an error and post the gh file?

Permalink Reply by David Rutten on July 12, 2016 at 7:31am

Without the files I couldn't possibly comment. I do know your formatting mask is not correct. I'm surprised it works at all. Can you test whether the number that is actually inside the [A] output of the area component is correct?

Permalink Reply by Jay Ramos on July 12, 2016 at 7:50am

umh, i think the issue is in the formatting mask, now that you point it out. (issue which is......??)

What is really weird is that usually when something is wrong, is wrong.
In this case, SOMETIMES is wrong, sometimes is right.
Look at the picture below: i didn't change anything nor in the file, nor in the GH definition. AND...it gives the right area this time!
I just played around with the curves to select: sometimes selecting 1, or 2, or first one then the other...and it came out correct this time.
Actually from now on, it always comes out correct, without having changed anything from when it was giving a false result.
Why? How? mystery.

Here you also find attached an excerpt of the whole thing. 'Of course' now it works good.

thanks

Attachments:

gh test.rar, 27 KB

Permalink Reply by Joseph Oster on July 12, 2016 at 8:25am

Where's there's mystery, there's no mastery. Where's there's mastery, there's no mystery.
-- Yogi Bhajan

Permalink Reply by David Rutten on July 12, 2016 at 9:26am

Welp, I can't even open that 3dm file without crashing Rhino. No idea why.

I can open the gh file but it doesn't have the curves internalised so I can't actually test it.

By the by your formatting mask should looks like this:

Format("A={0:0.0}m²", x)

You want to insert the value inside x at the position marked by {0}, with the optional formatting pattern '0.0'. Nothing else should appear inside the curly brackets because the 'A=' and the 'm²' are not part of the formatting process, they are merely bits of text in the vicinity of the values being formatted.

Permalink Reply by Jay Ramos on July 13, 2016 at 3:17am

thanks for the answer!

regarding the rhino file...i have no explanation, since it's a file with only 3 polylines in it! i wonder what can cause the crash.

i try to upload again the file itself....

So yesterday i said it was outputting the correct result.

Today not, even correcting the formatting mask...

:( sigh

Attachments:

GH test.3dm, 149 KB

Permalink Reply by David Rutten on July 13, 2016 at 3:46am

I just updated to the latest Rhino6 source and it still crashes (I was actually running a developer build that was over a month old yesterday). I'll create a YouTrack bug report, we'll see where it goes.

Permalink Reply by David Rutten on July 13, 2016 at 3:56am

Yeah, that file opened, and the numbers I'm getting are the same in both Rhino and Grasshopper. I can't see any problem with the geometry that might explain why the area calculator might get confused, I'm stumped.

It's not like GH re-implements the area algorithm, ultimately there is only one such piece of code and both Grasshopper and Rhino use it, so my first instinct would be to focus on the surrounding components, as those constitute the major differences, but seeing as I cannot get GH and Rhino to behave differently, I have no leads left to investigate.

Permalink Reply by Barry Mair on July 13, 2016 at 7:12am

Could it be the 'Corporate' version of Rhino that we tend to see on occasions?

Permalink Reply by David Rutten on July 14, 2016 at 3:58am

There is no corporate version, when you see that it means it's a cracked version. Rhino only comes in one version, but there are several different licenses (educational, lab, commercial, not-for-release developer builds, maybe more I can't remember).

Permalink Reply by Barry Mair on July 14, 2016 at 7:38am

I was referring to the images above!

Permalink Reply by David Rutten on July 14, 2016 at 7:58am

Well, cracked or not, still seems like a bug worth fixing if only we could track it down.