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ํŠน์ง•์ด๋ž€ ๊ฐ ํฌ์ธํŠธ๋“ค์ด ๊ฐ€์ง„ ๊ณ ์œ  ์„ฑ์งˆ๋กœ ๊ฐ ํฌ์ธํŠธ๋“ค์„ ๊ตฌ๋ถ„ ํ• ๋•Œ ์‚ฌ์šฉ ๋ฉ๋‹ˆ๋‹ค.

2D ์ด๋ฏธ์ง€ ๋ถ„์„์„ ๋‹ค๋ฃจ์–ด ๋ณด์‹  ๋ถ„์ด๋ผ๋ฉด ํŠน์ง•์ (Keypoint/Feature)์™€ ํŠน์ง• ๊ธฐ์ˆ ์ž(Feature descriptor)๋ผ๋Š” ์šฉ์–ด์— ๋Œ€ํ•˜์—ฌ ์•„์‹ค๊ฒƒ์ž…๋‹ˆ๋‹ค.

ํŠน์ง•์ ์ด๋ž€ ๊ทธ๋ฆผ์˜ ํŠน์ง•์„ ์ž˜ ๋‚˜ํƒ€๋‚ด์ค„ ์ˆ˜ ์žˆ๋Š” ๋ถ€๋ถ„์„ ์˜๋ฏธ ํ•ฉ๋‹ˆ๋‹ค. ๋Œ€ํ‘œ์ ์œผ๋กœ ๋‹ค๊ฐํ˜•์˜ ๊ผญ์ง€์ (corner)'์ด๋‚˜ '์„ ๋ถ„์˜ ๋์ ๊ฐ€ ์žˆ์Šต๋‹ˆ๋‹ค. ํŠน์ง•์ ์€ ๋ฌผ์ฒด ํƒ์ง€, ๋ฌผ์ฒด ์ถ”์ , ๋ฌผ์ฒด ๋งค์นญ๋“ฑ์— ์‚ฌ์šฉ๋ฉ๋‹ˆ๋‹ค. ํŠน์ง•์  ์ถ”์ถœ์„ ์œ„ํ•ด์„œ Harris, SIFT, FAST ์•Œ๊ณ ๋ฆฌ์ฆ˜๋“ค ์žˆ์Šต๋‹ˆ๋‹ค.

ํŠน์ง• ๊ธฐ์ˆ ์ž๋Š” ํŠน์ง•์ ์˜ ์ง€์—ญ์  ํŠน์„ฑ์„ ์„ค๋ช…ํ•ฉ๋‹ˆ๋‹ค. ๋”ฐ๋ผ์„œ ํŠน์ง•์ ๊ฐ„ ๋น„๊ต๊ฐ€ ๊ฐ€๋Šฅํ•ด ์ง‘๋‹ˆ๋‹ค. ๋Œ€ํ‘œ์ ์ธ ํŠน์ง• ๊ธฐ์ˆ ์ž๋Š” SIFT, HOG ๋“ฑ์ด ์žˆ์Šต๋‹ˆ๋‹ค.

3D ํฌ์ธํŠธ ํด๋ผ์šฐ๋“œ ๋ถ„์„์‹œ์—๋„ ์ด๋Ÿฌํ•œ ํŠน์ง•(Feature)์ •๋ณด๋“ค์„ ํ™œ์šฉ ํ•ฉ๋‹ˆ๋‹ค. ๋‹ค์Œ ์ฑ•ํ„ฐ์—์„œ ๋‹ค๋ฃฐ ๋ถ„๋ฅ˜๋ฌธ์ œ ํ•ด๊ฒฐ์„ ์œ„ํ•ด์„œ๋Š” ํ•„์ˆ˜์ ์ž…๋‹ˆ๋‹ค.

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์ž์„ธํ•œ ๋‚ด์šฉ์€ [์ด๊ณณ]์— ์ž˜ ๊ธฐ์ˆ  ๋˜์–ด ์žˆ์Šต๋‹ˆ๋‹ค.

1. Normal Estimation

์ ๊ตฐ์—์„œ ๊ตฌํ• ์ˆ˜ ์žˆ๋Š” Feature์ค‘์— ๊ฐ€์žฅ ๊ฐ„๋‹จํ•œ Surface Normal์— ๋Œ€ํ•˜์—ฌ ์‚ดํŽด ๋ณด๋„๋ก ํ•˜๊ฒ ์Šต๋‹ˆ๋‹ค. ๋จผ์ € Normal์€ ์‚ผ์ฐจ์› ๊ณต๊ฐ„์—์„œ๋Š” ๊ณต๊ฐ„์— ์žˆ๋Š” ํ‰๋ฉด ์œ„์˜ ํ•œ ์ ์„ ์ง€๋‚˜๋ฉด์„œ ๊ทธ ํ‰๋ฉด์— ์ˆ˜์ง์ธ ์ง์„ ์„ ์˜๋ฏธํ•ฉ๋‹ˆ๋‹ค. Normal์€ ํฌ๊ฒŒ ๊ผญ์ง€์  ๋ฒ•(Vertex Normals)๊ณผ ํ‰๋ฉด ๋ฒ•์„ (Face/surface Normals)๋กœ ๋‚˜๋ˆ„์–ด ์ง‘๋‹ˆ๋‹ค. ์—ฌ๊ธฐ์„œ๋Š” ํ‰๋ฉด ๋ฒ•์„ ๋งŒ์„ ๋‹ค๋ฃจ๊ณ  ์žˆ์œผ๋ฉฐ, ์ค„์—ฌ์„œ Normal์ด๋ผ๊ณ  ํ‘œ๊ธฐ ํ•˜์˜€์Šต๋‹ˆ๋‹ค.

Normal ์ข…๋ฅ˜

3D Surface Normal

์ •์˜ : The normal of a plane is an unit vector that is perpendicular to it

Normal Estimation์€ ์ƒ˜ํ”Œ๋ง ๋œ ๊ฐ’๋“ค๋กœ๋ถ€ํ„ฐ ๋ฐฉํ–ฅ ์ •๋ณด๋ฅผ ๋ณต์›ํ•ด ๋‚ด๋Š” ์ž‘์—…์„ ์˜๋ฏธ ํ•ฉ๋‹ˆ๋‹ค. ์—ฌ๊ธฐ์„œ ์ค‘์š”ํ•œ ๊ฒƒ์€ ์ƒ˜ํ”Œ๋ง๋œ ๊ฐ’๋“ค์ž…๋‹ˆ๋‹ค. ํ•œ์ ์˜ ๋ณด๋งŒ์œผ๋กœ๋Š” ๋ฒ•์„  ๋ฒกํ„ฐ๋ฅผ ๊ตฌํ• ์ˆ˜ ์—†์Šต๋‹ˆ๋‹ค. ๊ทธ๋ž˜์„œ ๊ตฌํ•˜๋ ค๊ณ  ํ•˜๋Š” ๋Œ€์ƒ ์ ์˜ ์ด์›ƒํ•œ ์ ๋“ค์ด ๊ฐ€์ง€๊ณ  ์žˆ๋Š” ๊ฐ’๋“ค์„ ์ด์šฉํ•˜๋ฉด ์ƒ˜ํ”Œ๋งํ•˜๊ธฐ ์ „์— ๊ทธ ์ ์„ ํฌํ•จํ•˜๊ณ  ์žˆ๋˜ ๋ฉด์˜ ๋ฒ•์„  ๋ฒกํ„ฐ๋ฅผ ๊ทผ์‚ฌ์ ์œผ๋กœ ์ถ”์ • ํ• ์ˆ˜ ์žˆ๋‹ค. ์ด๋ ‡๊ฒŒ ๋Œ€์ƒ์ ์„ ์ค‘์‹ฌ์œผ๋กœ ํ•œ ๊ตญ์†Œ์ ์ธ ์ •๋ณด๋กœ ๋ถ€ํ„ฐ ๊ตฌํ•ด ๋‚ธ ๋ฒ•์„  ๋ฒกํ„ฐ๋ฅผ ์ถ”์ • ๋ฒ•์„  ๋ฒกํ„ฐ(estimated normal)๋ผ ํ•ฉ๋‹ˆ๋‹ค. PCL์—์„œ๋Š” ์ƒ˜ํ”Œ๋ง ๋ฐฉ๋ฒ•์œผ๋กœ ์ด์ „์žฅ์—์„œ ์‚ดํŽด๋ณธ Octree Search๋ฅผ ์‚ฌ์šฉํ•ฉ๋‹ˆ๋‹ค.

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Integral images๋„ normal estimation๋ฐฉ๋ฒ• ์ค‘ ํ•˜๋‚˜์ž…๋‹ˆ๋‹ค. ํ•˜์ง€๋งŒ RGB-D์„ผ์„œ๋“ฑ์—์„œ ์–ป์€ organized clouds๋ฅผ ๋Œ€์ƒ์œผ๋กœ ํ•˜๊ณ  ์žˆ์–ด ์—ฌ๊ธฐ์„œ๋Š” ๋‹ค๋ฃจ์ง€ ์•Š์Šต๋‹ˆ๋‹ค.

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https://laonple.blog.me/221195959435

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