Bullet: btCollisionWorld::contactTest doesn't work

Question

I added some boxes in a collision world, then use btCollisionWorld::contactTest to test if any box contact with a given sphere. Below is the code:

    int SpacePhysics::SphereContactTest(const btVector3 &center, btScalar radius) {
        btSphereShape *sphere_shape = new btSphereShape(radius);
        btCollisionObject *sphere = new btCollisionObject();
        sphere->setCollisionShape(sphere_shape);
        sphere->setWorldTransform(btTransform(btQuaternion(), center));
        collision_world_->contactTest(sphere, result_callback);
        delete sphere;
        delete sphere_shape;
        return result_callback.hit_count;
    }

However no contact can be detected(when it should), if I use btCollisionWorld::contactPairTest to test the sphere with all the collision objects in the world, the contacts can be detected. But using btCollisionWorld::contactTest nothing can be detected. What's the proper way to use btCollisionWorld::contactTest?

Answer 1

Found the reason:

sphere->setWorldTransform(btTransform(btQuaternion(), center));

set the sphere with a invalid transform, therefore no collision can be detect. Although I don't understand why contactPairTest can still detect collision.