From: Hans Hagen via ntg-context <ntg-context@ntg.nl>
To: ntg-context@ntg.nl
Cc: Hans Hagen <j.hagen@xs4all.nl>
Subject: Re: atan2 function
Date: Fri, 14 Oct 2022 10:07:19 +0200 [thread overview]
Message-ID: <bd569b68-b996-caee-40ac-1e0ca0330d10@xs4all.nl> (raw)
In-Reply-To: <b36283d0b4e89cf0cb2b41687eb684fb2d323dfd.camel@telus.net>
On 10/14/2022 2:35 AM, Max Chernoff via ntg-context wrote:
>
> Hi,
>
>> The angle function doesn't appear to provide the same calculation as
>> my atantwo in all cases.
>
> They both give the same results, but "angle" gives a result in degrees
> while "atantwo" gives a result in radians. This demo:
>
> \startMPpage
> vardef atantwo( expr dy, dx ) =
> save theta;
>
> numeric theta;
>
> theta := 0;
>
> if (dx > 0):
> theta := atan( dy / dx );
> elseif (dx < 0) and (dy >= 0):
> theta := atan( dy / dx ) + pi;
> elseif (dx < 0) and (dy < 0):
> theta := atan( dy / dx ) - pi;
> elseif (dx == 0) and (dy > 0):
> theta := pi / 2;
> elseif (dx == 0) and (dy < 0):
> theta := -pi / 2;
> fi;
>
> theta
> enddef;
>
> def showangles(expr dx, dy) =
> message "---------------"
> message "atantwo " & decimal atantwo(dy, dx)
> message "angle " & decimal (angle(dx, dy) * pi / 180)
> message "angle " & decimal angle(dx, dy)
> message "(" & decimal dx & ", " & decimal dy & ")"
> enddef;
>
> showangles(1, 0);
> showangles(1, 1);
> showangles(0, 1);
> showangles(-1, 1);
> showangles(-1, 0);
> showangles(-1, -1);
> showangles(0, -1);
> showangles(1, -1);
> \stopMPpage
So you suggest to add atantwo? As side note, you can redure your
definition to:
vardef atantwo( expr dy, dx ) =
if (dx > 0):
atan( dy / dx )
elseif (dx < 0) and (dy >= 0):
atan( dy / dx ) + pi
elseif (dx < 0) and (dy < 0):
atan( dy / dx ) - pi
elseif (dx == 0) and (dy > 0):
pi / 2
elseif (dx == 0) and (dy < 0):
-pi / 2
else :
0
fi
enddef ;
and then
vardef atantwo(expr dy, dx) =
if dx == 0 :
if dy < 0 : - fi pi / 2
else :
atan(dy/dx) if dx > 0 : if dy < 0 : - else : + fi pi fi
fi
enddef ;
going further makes us end up in an one-line obscurity
Hans
-----------------------------------------------------------------
Hans Hagen | PRAGMA ADE
Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
tel: 038 477 53 69 | www.pragma-ade.nl | www.pragma-pod.nl
-----------------------------------------------------------------
___________________________________________________________________________________
If your question is of interest to others as well, please add an entry to the Wiki!
maillist : ntg-context@ntg.nl / https://www.ntg.nl/mailman/listinfo/ntg-context
webpage : https://www.pragma-ade.nl / http://context.aanhet.net
archive : https://bitbucket.org/phg/context-mirror/commits/
wiki : https://contextgarden.net
___________________________________________________________________________________
next prev parent reply other threads:[~2022-10-14 8:07 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-13 5:40 Thangalin via ntg-context
2022-10-13 6:42 ` Max Chernoff via ntg-context
2022-10-13 19:51 ` Thangalin via ntg-context
2022-10-14 0:35 ` Max Chernoff via ntg-context
2022-10-14 8:07 ` Hans Hagen via ntg-context [this message]
2022-10-14 14:40 ` Alan Braslau via ntg-context
2022-10-14 18:59 ` Thangalin via ntg-context
2022-10-14 22:42 ` Alan Braslau via ntg-context
2022-10-14 23:09 ` Thangalin via ntg-context
2022-10-15 1:22 ` Alan Braslau via ntg-context
2022-10-14 12:26 ` Alan Braslau via ntg-context
2022-10-14 12:58 ` Taco Hoekwater via ntg-context
2022-10-14 13:05 ` luigi scarso via ntg-context
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=bd569b68-b996-caee-40ac-1e0ca0330d10@xs4all.nl \
--to=ntg-context@ntg.nl \
--cc=j.hagen@xs4all.nl \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).