ba­sics: utilise the Knife

In our con­tin­u­ing se­ries of CGI ba­sics we look at us­ing the knife tool

3D World - - CONTENTS - Mike Griggs Mike Griggs is a 3D and vis­ual ef­fects artist with vast ex­pe­ri­ence across the in­dus­try, as both a cre­ator and a tech­ni­cal writer. www.cre­ative­bloke.com

Tips for us­ing the knife tool

I ex­ist­ing ge­om­e­try or has the abil­ity to slice through ev­ery­thing due to a creative de­ci­sion.

Alas not all im­ple­men­ta­tions of a cut­ting tool are the same. Some ap­pli­ca­tions give more op­tions than others, most will en­able free-form cut­ting along the face of a model, but only a few of­fer view­port-based cut­ting.

Some cut­ting tools of­fer the abil­ity to cre­ate gaps when slic­ing; this can be re­ally use­ful for all kinds of mod­el­ling tasks, es­pe­cially when the soft­ware can cap the open cuts. This is be­cause in most 3D ap­pli­ca­tions meshes are seen as shells rather than be­ing solid; there are some ap­pli­ca­tions that can see meshes as solid, but you’ll find that they f you’re new to CGI you may feel that there are far too many tools to choose from in a dizzy­ing ar­ray of soft­ware. This se­ries aims to break ev­ery­thing in CGI down to the very ba­sics, so that ev­ery artist can be armed with the knowl­edge of which tool is best. This time we are look­ing at the knife func­tion.

It goes by many names: knife, slice or cut to name but a few, but ef­fec­tively the im­ple­men­ta­tion is the same – it cuts through poly­gons and edges to ei­ther split ob­jects up or to cre­ate new bound­aries within a mesh from which to cre­ate new ge­om­e­try.

A good slic­ing tool should en­able an artist to cut ei­ther in a way that is sym­pa­thetic to the are usu­ally lim­ited to CAD and sculpt­ing ap­pli­ca­tions.

Some ap­pli­ca­tions of­fer the abil­ity to cre­ate curved slices, which is use­ful for cre­at­ing or­ganic shapes, and if the ap­pli­ca­tion has the abil­ity to place im­ages in the view­port as a guide, us­ing a curved knife tool is a great way to match ref­er­ence.

Even if the slice tool does not of­fer a curved tool, us­ing a slice or knife tool on a sin­gle poly­gon can be great way to start a model.

The other area where a cut­ting tool can be use­ful is in defin­ing poly­gon flow on meshes that are go­ing to be an­i­mated, as well as for mak­ing sure that n-gons are di­vided into quads or tri­an­gles for model ex­port.

Au­thor

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