Many Kammaṭṭhāna (working places, or themes of meditation/reflection/visualisation), which are taught by the Buddha, are actually visualisations in regard of signs.
- the 10 kasinas (certain colors, elements
(as less distructing for the mind)
- tenkind of corpse
- (parts of) the body (kāya)
(as to gain disenchantment in regard of form)
Especially objects in signs have the purpose to concentrate the mind. In regard of the objects of repulsion, they also give ground for transcendent form by focusing on it.
The other objects are visualisations of virtues (of the Buddha, Dhamma, Sangha) or reflections on own virtues (generosity, conduct, virtues like Devas) and then there are certain other visualisations of thoughts to more directly "change" ones level of awarness.
All, how ever, are used to gain certain concentrations used on one hand as proper dwellings, livelihood for the mind on one hand and as object of investigation for insight.
Since the prerequisite to gain absorbed concentration is the (a good amount) abounding from sensuality, such as visualization of grave stimulating objects of form, beautifullness in form, form to identify one self with it or even such as "bodily sequences" are not found in the advices of the Buddha, with is also clear when remembering that to transcendent form is the very first step.
Where ever such kinds of meditations are found,they can be content regarded as "this is not the teaching of the Buddha".
It's pupose might be what ever kind of "illusion" one might objecting with it or what ever identification one tries to pursue with such, but certainly not for release, undinging, Nibbana. It might be also of use for wordily special powers.
Again, if reflecting on Deities and Devas, one is encouraged to remember virtues one has (means there must be experians to be able to visualise) equal them.
Form and material qualities are not regarded as graspworthy at all but obstacles for any useful one-pointness or for inside, aside of those giving disgust to it.
A person, having grasped after seeing the Buddha in Form, when finally met him was taught clearly that seeking after form makes no sense, not lasting as it is: "Who ever sees the Dhamma, sees the Tathagata, who ever sees the Tathagata, sees the Dhamma." It should be clear, that this does not put into hope that lasting, real Form can be found or worthy to seek after.
[Note: This is a gift of Dhamma and not meant for commercial purpose or other low wordily gains by means of trade and exchange.]