comp.lang.idl-pvwave archive: archive » Re: pixel coordinates of a line

Home » Public Forums » archive » Re: pixel coordinates of a line

Show: Today's Messages :: Show Polls :: Message Navigator
E-mail to friend

Re: pixel coordinates of a line [message #25543 is a reply to message #25539]

Thu, 28 June 2001 06:33

tam
Messages: 48
Registered: February 2000

Member

Marc Schellens wrote:
>
> Oh, I forgot:
> I have the start and endpoint, but they might need to be clipped
> to the images boders...
>
>> I want to extract pixels along a line.
>> I know start and endpoint (ie. I draw the line in top of the
>> image).
>> How to get the pixel values? Do I have to do it 'by hand'?
>>
>> thanks,
>> marc

Working in pixel coordinates you have the endpoints (sx,sy,ex,ey) and the clipping
rectangle (x0,y0, x1, y1), so you should trivially be able to get the equation
of the line

y = m x + b [ m= (ey-sy)/(ex-sx), b = sy - m sx ]

Turn this into IDL...

x = lindgen(x1-x0) + x0
y = floor (m * x + b + 0.5) [add 0.5 to get appropriate rounding]
w = where (y ge y0 and y le y1)
if (w[0] ne -1) then begin
x = x(w)
y = y(w)
endif else begin
.... line is outside clipping rectangle
endelse

Here I'm assuming integral values for x0,x1, y0,y1 but not necessarily the
end points.

There are probably subtleties I've missed but this seems like a reasonable
start. Whether it will exactly match the pixels that IDL will draw on
is hard to say... Guess we'd need to know exactly how IDL draws a line.

Tom McGlynn
NASA/GSFC
tam@lheapop.gsfc.nasa.gov
[Mailed and posted]

Report message to a moderator

[Message index]

		Re: pixel coordinates of a line By: marc schellens[1] on Fri, 29 June 2001 01:45
		Re: pixel coordinates of a line By: Craig Markwardt on Thu, 28 June 2001 08:10
		Re: pixel coordinates of a line By: david[2] on Thu, 28 June 2001 07:42
		Re: pixel coordinates of a line By: tam on Thu, 28 June 2001 06:33
		Re: pixel coordinates of a line By: Alex Schuster on Thu, 28 June 2001 05:43
		Re: pixel coordinates of a line By: marc schellens[1] on Wed, 27 June 2001 23:35
		Re: pixel coordinates of a line By: david[2] on Fri, 29 June 2001 06:53
		Re: pixel coordinates of a line By: Craig Markwardt on Fri, 29 June 2001 06:22

Previous Topic:	volume slicing
Next Topic:	Re: Intersecting geometric shapes

-=] Back to Top [=-

[ Syndicate this forum (XML) ] [

] [

]

Current Time: Sat Oct 11 01:54:13 PDT 2025

Total time taken to generate the page: 0.00188 seconds