Court experts are special class of expert witnesses that are appointed / summoned / subpoenaed by the court — as opposed to being called by the parties. In New Zealand the procedure is set out in r 9.36 and the following rules. Court experts can be appointed both on an application by a party and on the court's own volition.
As explained in McGechan on Procedure:
The procedure has not been widely used, probably because it goes against the traditionally adversarial way in which litigation has been conducted: each party would rather bring along its own expert, hoping to discredit the other's expert in cross-examination, but ultimately leaving it to the Court to choose between them. Appointment of a single expert by the Court has the advantage of possibly resolving a significant issue without the need for any evidence at all.
(Interestingly, what a court expert tells is not considered evidence — unlike if it was a regular expert witness).
In nut shell, if a party wants the court to appoint a court expert, the party first needs to try to reach an agreement with the other parties on whom to appoint. Ultimately the court will decide who it will be (if anyone) from the list of candidates proposed by the parties.
What is vague to me is whether the expert has to agree to be appointed. In case of regular expert witnesses they obviously are free to appear or not. But is it he same with court experts? Can a party simply nominate experts they wish to hear and apply to the court for their appointment, without even contacting them beforehand? Or does the party need to obtain the proposed experts' consent first?
(Any jurisdiction with adversarial system.)