| closed contour paths: clockwise or anticlockwise - or actually a mixture? [message #87069] |
Fri, 03 January 2014 12:53  |
George.millward
Messages: 26
Registered: October 2012
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Junior Member |
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Hi there,
I'm doing some very straightforward contour plotting - but instead of actually plotting the contours - I'm writing out the path data of closed contours by using the path_info and path_xy keywords.
This is all working fine, but I have a problem: Some of the contour paths (written out as x,y arrays) close in a clockwise order, some close in an anticlockwise order. This is causing trouble when I export the paths to other mapping software because the latter is strictly wanting the paths to always be clockwise.....
Does anyone have any insight into this? Is there some keyword I am missing?
alternatively is there a simple way to establish whether a path is clockwise or anticlockwise so the arrays can be reversed if necessary?
Cheers
George.
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| Re: closed contour paths: clockwise or anticlockwise - or actually a mixture? [message #87070 is a reply to message #87069] |
Fri, 03 January 2014 13:01  |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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George.millward@yahoo.com writes:
>
> Hi there,
>
> I'm doing some very straightforward contour plotting - but instead of actually plotting the contours - I'm writing out the path data of closed contours by using the path_info and path_xy keywords.
>
> This is all working fine, but I have a problem: Some of the contour paths (written out as x,y arrays) close in a clockwise order, some close in an anticlockwise order. This is causing trouble when I export the paths to other mapping software because the latter is strictly wanting the paths to always be clockwise.....
This seems unlikely. Are you sure you are not confusing the high and low
contours? In other words, one path describes a mound, the other path
describes a hole. The normal should be pointing toward you in the
counterclockwise (mound) contour, and away from you in the clockwise
(hole) contour.
Cheers,
David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.idlcoyote.com/
Sepore ma de ni thue. ("Perhaps thou speakest truth.")
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| Re: closed contour paths: clockwise or anticlockwise - or actually a mixture? [message #87071 is a reply to message #87070] |
Fri, 03 January 2014 13:13 |
George.millward
Messages: 26
Registered: October 2012
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Junior Member |
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On Friday, January 3, 2014 2:01:23 PM UTC-7, David Fanning wrote:
> George.millward@yahoo.com writes:
>
>
>
>>
>
>> Hi there,
>
>>
>
>> I'm doing some very straightforward contour plotting - but instead of actually plotting the contours - I'm writing out the path data of closed contours by using the path_info and path_xy keywords.
>
>>
>
>> This is all working fine, but I have a problem: Some of the contour paths (written out as x,y arrays) close in a clockwise order, some close in an anticlockwise order. This is causing trouble when I export the paths to other mapping software because the latter is strictly wanting the paths to always be clockwise.....
>
>
>
> This seems unlikely. Are you sure you are not confusing the high and low
>
> contours? In other words, one path describes a mound, the other path
>
> describes a hole. The normal should be pointing toward you in the
>
> counterclockwise (mound) contour, and away from you in the clockwise
>
> (hole) contour.
>
>
>
> Cheers,
>
>
>
> David
>
> --
>
> David Fanning, Ph.D.
>
> Fanning Software Consulting, Inc.
>
> Coyote's Guide to IDL Programming: http://www.idlcoyote.com/
>
> Sepore ma de ni thue. ("Perhaps thou speakest truth.")
David,
Aha - I think that's it. Thanks. I think a contour that is 'high' (above it's surroundings) is written in clockwise order - but if it is a 'hole' it is written is anti-clockwise order. Is that your understanding?
[For anyone trying to follow this thread the relevant parameter here is path_info.high_low]
Cheers
George.
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