Rise Posted September 29, 2008 Share Posted September 29, 2008 Hi, I'm trying to find the area of a segment of a circle with a hole in the center of it (think pizza slice with a hole in the center of the pie). My drawing is composed of a couple of arcs (trimmed circles) and 2 lines to form the borders. I couldn't figure out how to find the area using AutoCAD so I have been trying to figure out the area using basic math but I'm unsure of my methods enough to worry about if its correct or not I know, I know, I'm an idiot 1st - is there a way to find this out in autocad so I don't have to use my brain?? 2nd - since I did use my brain, this is what I did: pi*r^2(outer radius)-pi*r^2(inner radius) * (1 - (border angle*2)/360) = area The way the segment was drawn, the angle to the first border is 157.5 degrees and it's a symmetrical segment. So that is why I multiplied it by 2 to get 315 degrees and then ratio'd it to 360 degrees which gave me .875... 1-.875 = .125 and so my segment is 1/8 of a circle. so 1/8th times the circle area formula should give me the area of the segment... right? Quote Link to comment Share on other sites More sharing options...
Secretagdan Posted September 29, 2008 Share Posted September 29, 2008 Pedit --> Join & Close.. then List your single polyline. This will give you your area. You can use this to double-check your math. Quote Link to comment Share on other sites More sharing options...
GhostRider Posted September 29, 2008 Share Posted September 29, 2008 one way is to use the BPOLY command and get the area from the properties of the poly line it creates. there are others I'm sure but this is one simple way Quote Link to comment Share on other sites More sharing options...
Rise Posted September 29, 2008 Author Share Posted September 29, 2008 Thanks guys, that helped a lot. Turns out I'm not a complete idiot Quote Link to comment Share on other sites More sharing options...
Tiger Posted September 29, 2008 Share Posted September 29, 2008 Hi, I'm trying to find the area of a segment of a circle with a hole in the center of it (think pizza slice with a hole in the center of the pie). My drawing is composed of a couple of arcs (trimmed circles) and 2 lines to form the borders. I couldn't figure out how to find the area using AutoCAD so I have been trying to figure out the area using basic math but I'm unsure of my methods enough to worry about if its correct or not I know, I know, I'm an idiot 1st - is there a way to find this out in autocad so I don't have to use my brain?? 2nd - since I did use my brain, this is what I did: pi*r^2(outer radius)-pi*r^2(inner radius) * (1 - (border angle*2)/360) = area The way the segment was drawn, the angle to the first border is 157.5 degrees and it's a symmetrical segment. So that is why I multiplied it by 2 to get 315 degrees and then ratio'd it to 360 degrees which gave me .875... 1-.875 = .125 and so my segment is 1/8 of a circle. so 1/8th times the circle area formula should give me the area of the segment... right? Just because I'm bored I looked through your mathematical solution. What I found in my old formula book is that the Area should be ((pi*r(outer)^2)-(pi*r(inner)^2)) * (segmentangle/360) If I read your description, your segment goes from 157.5 degrees to 315degrees - i.e. the segment is 45degrees. And 45/360 is also 1/8, just as (1-((157.5*2)/360)) is 1/8. so your math was right too Quote Link to comment Share on other sites More sharing options...
Rise Posted September 29, 2008 Author Share Posted September 29, 2008 thanks for confirming, Tiger! Quote Link to comment Share on other sites More sharing options...
SuperCAD Posted September 29, 2008 Share Posted September 29, 2008 You can also hatch the area you want to calc and then select the hatch and look at the Area value in properties. Quote Link to comment Share on other sites More sharing options...
Lihualee Posted September 29, 2008 Share Posted September 29, 2008 bump and lurk Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.