The ideas suggested here for America are probably good ones, but the controversy was begun by Police being concerned about security around the Royal Wedding next year in Windsor UK.
It would be a bit difficult to provide large areas of open-air or trailer-type accommodation for rough sleepers in UK cities, due to lack of space, cost of facilities etc. But triage for them might be a possibility, to sort through their many problems and difficulties and address each individual's needs. Addictions and mental/physical ill-health could be treated. But no-one could physically force them to attend or participate, unless rather overbearing legislation was brought into force.
I agree wholeheartedly with Joe regarding respecting their personal dignity.
It wrings my heart when we go into Norwich and pass quite a few of these poor souls, especially in the freezing weather. We often buy a coffee and a pack of sandwiches for one or two. But it isn't the answer I know.