SYDNEY, Jan 16 (Reuters) – Copper prices edged up in London and Shanghai markets on Tuesday, helped by a weaker U.S. dollar. The dollar index against a basket of six major currencies was hovering just above its weakest level since January, 2015. A weaker greenback makes dollar-denominated commodities cheaper for holders of other currencies. A decision on Monday by the People’s Bank of China (PBOC) to lift the yuan’s official midpoint to the greenback to a 1-1/2 year high was also supporting copper prices. “The moves by the PBOC to raise the fixing of the yuan against the U.S. dollar helped improve the already positive sentiment in the market,” ANZ Bank said. FUNDAMENTALS: * LONDON COPPER: Three-month copper on the London Metal Exchange had edged up 0.15 percent to $7,221 a tonne by 0250 GMT. * SHANGHAI COPPPER: The most-traded copper contract on the Shanghai Futures Exchange was up 0.16 percent at 54,750 yuan ($8,514.77) a tonne. * RIO TINTO: Rio Tinto stuck to a 2018 production target of 510,000-610,000 tonnes of mined copper and 225,000-265,000 tonnes of refined copper. Aluminium production is targeted at 3.5-3.7 million tonnes. For 2017, aluminium production eased 1 percent and mined copper output fell 9 percent. * CHINA GDP: China’s economic growth is expected to have slowed slightly in the fourth quarter from the previous quarter, a Reuters poll showed, as the government extended a crackdown on debt risks and factory pollution. * YUAN: China’s central bank on Monday lifted its official yuan midpoint to the highest level in more than over 1-1/2 years, to 6.4574 per dollar, reflecting solid spot yuan performance on Friday and broad dollar weakness in overseas markets. * CME COPPER: CME Group won a bigger slice of the copper market in 2017 from its rivals in London and Shanghai, a Reuters analysis of exchange data showed, a trend that is expected to continue though this year. * OTHER METALS: ShFE aluminium, zinc and lead were modestly lower, while nickel and tin inched up.