Message: 2 Date: Thu, 29 Jan 2004 15:26:38 -0800 (PST) From: Alejandro Tejada <[EMAIL PROTECTED]> Subject: Re: Points in a circular area To: [EMAIL PROTECTED] Message-ID: <[EMAIL PROTECTED]> Content-Type: text/plain; charset=us-ascii
on Thu, 29 Jan 2004 Dar Scott wrote:
Some years ago I designed a model and library for working with abstractions of drawings and paintings in a functional (that is f() manner) way.
In that model the plane could be partitioned by a
line or by a circle and other shapes. A pie shape is the union (ANDing) of two line
partitions and a circle partition.
For this particular case, it might be easier for you to arctan2 points relative to the center to see if they are in the right angle range and then check the distance to see if that is small enough.
If i interpret right your recommendations, it's similar to the procedure that Jim Hurley is suggesting to use. Now, i'll code a solution and post the script for speed enhancements. ;-)
In rendering (or creating point lists) I am trying
to use interval arithmetic and am putting that off
until some performance changes in Revolution. This method allows tests to work on
whole zones of pixels in one calculation.
This sounds useful. Could externals helps for these tasks?
The line tests will be faster than the arctan2
tests for this method, because of the ignorance
involved in interval arithmetic.
I've read that assembler code is faster than c code.
In the mean time you might try testing each pixel (I assume you mean pixels) in the bounding rect of the circle of which the arc is part.
Let's see how much time does this calculation takes.
Al,
Just for an estimate of the time needed for the trial and error method, I ran the following handler:
on mouseUp
put 30 into tAngle
put 100 into R
put "" into results
put the sec into startTime
startTurtle
repeat with x = 0 to R
repeat with y = 0 to R
put raCor(x,y) into ra
--Test to see if the point x,y is in the wedge.
if item 1 of ra < R and item 2 of ra < tAngle then put x,y & return after results
end repeat
end repeat
put results into field 1
put the sec - starttime
beep
end mouseUp
It determines all integer coordinates inside a circular wedge of radius R (100) and arc tAngle (30 degrees). There are 2,666 points and it takes a little over a second to compute.
(The function raCor(x,y) returns the radial coordinates (radius and angle) corresponding to the rectangular coordinates x,y.)
Hope this gives you some idea on times.
Jim
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