Three js recognizing shapes

Questions
1

Recognize the uploaded obj is cylinder or Not how to do that

2

Quite literally your only option, unless you set up specific boundaries of what defines a cylinder (shape / level of detail / lids / dents / aspect ratio, there’s quite a lot of properties - and modifying any even slightly can technically turn a cylinder into a sphere / cube)

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3

The objs are literally created from blender does that help in anyway

4

Nope, geometry is geometry - what you’re looking for is a way to define what is a cylinder in a mathematical way - what separates the shape you’re looking for from all the other shapes.

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5

Before the AI ​​Era, OpenCV was an incredible image analysis tool, made in c++
I know that it is capable of doing this, and I know that there is also a javascript version of it.

and
https://docs.opencv.org/4.x/d5/d10/tutorial_js_root.html

6

Open the OBJ file and see if there is any metadata that blender may have stored on the objects…

Like maybe its named “cylinder” or has a comment indicating what generated it.

Otherwise, this is basically a doomed concept.

If you could explain why you need to identify cylinders, we might be able to offer some more practical approaches.

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7

I need to scale an OBJ file. If the object is a cylinder type, when its length is increased, the breadth should also increase proportionally, and vice versa. For other shapes, the object should scale based on its length, breadth, and height."

8

https://didisoftwares.ddns.net/6/index.html
I needed to add this to scale models based on height by importing a model of whatever height into tpose, needed because skinedmesh its hard to get correct box when skelleton changed pose,
Maybe you can give some idea of ​​something easier if you don’t have a skeleton

this.options.modelsize its a constant height defines model size
used fixModelScale(model)

_expandAABB(skinnedMesh, aabb) {
        var vertex = new THREE.Vector3();
        var temp = new THREE.Vector3();
        var skinned = new THREE.Vector3();
        var skinIndices = new THREE.Vector4();
        var skinWeights = new THREE.Vector4();
        var boneMatrix = new THREE.Matrix4();
        var skeleton = skinnedMesh.skeleton;
        var boneMatrices = skeleton.boneMatrices;
        var geometry = skinnedMesh.geometry;
        var index = geometry.index;
        var position = geometry.attributes.position;
        var skinIndex = geometry.attributes.skinIndex;
        var skinWeight = geometry.attributes.skinWeight;
        var bindMatrix = skinnedMesh.bindMatrix;
        var bindMatrixInverse = skinnedMesh.bindMatrixInverse;
        skeleton.update();
        function expand() {
            vertex.applyMatrix4(bindMatrix);
            skinned.set(0, 0, 0);
            for (var j = 0; j < 4; j++) {
                var si = skinIndices.getComponent(j);
                var sw = skinWeights.getComponent(j);
                boneMatrix.fromArray(boneMatrices, si * 16);
                temp.copy(vertex).applyMatrix4(boneMatrix).multiplyScalar(sw);
                skinned.add(temp);
            }
            skinned.applyMatrix4(bindMatrixInverse);
            aabb.expandByPoint(skinned);
        }
        if (index !== null) {
            for (var i = 0; i < index.count; i++) {
                vertex.fromBufferAttribute(position, index.getX(i));
                skinIndices.fromBufferAttribute(skinIndex, index.getX(i));
                skinWeights.fromBufferAttribute(skinWeight, index.getX(i));
                expand();
            }
        } else {
            for (var i = 0; i < position.count; i++) {
                vertex.fromBufferAttribute(position, i);
                skinIndices.fromBufferAttribute(skinIndex, i);
                skinWeights.fromBufferAttribute(skinWeight, i);
                expand();
            }
        }
    }
getModelBox3D(object3D) {
        var aabb = new THREE.Box3();
        var matrixWorld = new THREE.Matrix4();
        var skinnedMeshes = [];
        // Traverse the object3D to find all SkinnedMeshes
        object3D.traverse(function(child) {
            if (child.isSkinnedMesh && child.skeleton) {
                skinnedMeshes.push(child);
            }
        });
        if (skinnedMeshes.length === 0)
            return;
        // Expand the AABB to include all SkinnedMeshes
        skinnedMeshes.forEach(skinnedMesh => {
            var tempAABB = new THREE.Box3();
            this._expandAABB(skinnedMesh, tempAABB);
            tempAABB.applyMatrix4(skinnedMesh.matrixWorld);
            aabb.union(tempAABB);
        }
        );        
        return aabb;
    }

 fixModelScale(object3D) {
        //put model on TPOSE       
        // Calculate the bounding box of the newModel        
        let modelSize = new THREE.Vector3();
        this.getModelBox3D(object3D).getSize(modelSize);
        let biggervalue = Math.max(modelSize.x, modelSize.y, modelSize.z);
        //reescale to maintain aspect ratio
        let newscale = this.options.modelsize / biggervalue;
        object3D.scale.multiplyScalar(newscale);
        if (object3D.userData.mixamo == undefined)
            object3D.userData.mixamo = {};
        object3D.userData.mixamo.scale = newscale;
        //put hips on same position
        return object3D;
    }
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