Unconstitutional to ban homeless sleeping outside: http://www.washingtonpost.com/news/wonkblog/wp/2015/08/13/its-unconstitutional-to-ban-the-homeless-from-sleeping-outside-the-federal-government-says/ (“Such laws, the DOJ argues, violate the Eighth Amendment protections against cruel and unusual punishment, making them unconstitutional.”)
The McKinney–Vento Homeless Assistance Act of 1987 (Pub. L. 100-77, July 22, 1987, 101 Stat. 482, 42 U.S.C. § 11301 et seq.) is a United States federal law that provides federal money for homeless shelter programs. It was the first significant federal legislative response to homelessness, and was passed and signed into law by President Ronald Reagan on July 22, 1987. The act has been reauthorized several times over the years.
The McKinney Act originally had fifteen programs providing a spectrum of services to homeless people, including the Continuum of Care Programs: the Supportive Housing Program, the Shelter Plus Care Program, and the Single Room Occupancy Program, as well as the Emergency Shelter Grant Program.