Improve company productivity with a Business Account.Sign Up

x
?
Solved

rotating problem

Posted on 1998-10-07
3
Medium Priority
?
253 Views
Last Modified: 2010-04-16
I want to rotate an object.
I have found a way to do that but I need a
formula that gets an angle out of the sin() or cos()
of it.
( I have the angle (a) and I want to find the X ->  
  sin(X) = a )
0
Comment
Question by:yyyannag
  • 2
3 Comments
 
LVL 5

Accepted Solution

by:
scrapdog earned 400 total points
ID: 1215759
For each coordinate of the old image, the new coordinate can be found by using this formula:

OldImageX = NewImageX * cos(theta) - NewImageY * sin(theta)
OldImageY = NewImageX * sin(theta) + NewImageY * cos(theta)

(theta is angle in radians)


NewImageX and Y is the new, rotated image coordinates.  OldImage is the coordinates to extract the pixel from the old image.

Example:


  for i := 0 to NewSprite.Width - 1 do
    for j := 0 to NewSprite.Height - 1 do begin
      nx := (round(x*Cos(A)-y*Sin(A)));
      ny := (round(x*Sin(A)+y*Cos(A)));
      Sprite[i,j] := OldSprite[nx,ny];
    end;


Note that A must be in radians.  To convert from degrees to radians, you multiply by (pi/180).

Example:  the sin of 45 degrees would be

sin(45*pi/180);

In your question, you said you wanted to find X if sin(x) = a.  This would entail finding the inverse sin of a.  I don't know why you would want to find this.  But if you really need to know how to calculate an inverse sin in pascal:

function arcsin(x:real):real;
begin
  arcsin := arctan(x/sqrt(1-sqr(x)));
end;


If you send the function a real value (from -1 to 1 inclusive, the range of the sin function), it will return an angle in radians.

This function will have no practical purpose in rotating something, so consider looking over calculations again.

But your question also says you have the angle.  If you want to find the sin of the angle (which is probably what you want to do) you simply use the sin function:

X := sin(a);  {a is in radians; see note above}


Your formula, sin(x) = angle, would NEVER be used in any practical calculation anywhere.

Try using the formulas I gave you above (OldImageX..etc.) and if that is not what you want let me know.
0
 
LVL 5

Expert Comment

by:scrapdog
ID: 1215760
I made I typo in my answer!! Change this line:


      Sprite[i,j] := OldSprite[nx,ny];

to this:


      NewSprite[i,j] := OldSprite[nx,ny];
0
 
LVL 2

Author Comment

by:yyyannag
ID: 1215761
Thanks for the formula, it was very helpful
0

Featured Post

Upgrade your Question Security!

Your question, your audience. Choose who sees your identity—and your question—with question security.

Question has a verified solution.

Are you are experiencing a similar issue? Get a personalized answer when you ask a related question.

Have a better answer? Share it in a comment.

Join & Write a Comment

What is Archiving? Archiving in Exchange Online (called In-Place Archiving) provides users with additional mailbox storage space.
Read this article to learn how to migrate data from SharePoint to SharePoint Online account. The entire process of SharePoint migration is described in detail.
When you have multiple client accounts to manage, it often feels like there aren’t enough hours in the day. With too many applications to juggle, you can’t focus on your clients, much less your growing to-do list. But that doesn’t have to be the cas…
Through the video, you can check the migration process of Outlook PST file to PDF. Kernel for Outlook to PDF tool can convert Outlook emails with all attributes like Subject, To, From, Cc, Bcc and other folders such as Inbox, Outbox, Sent Items, Jun…

584 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question