  We have observed three near-Earth objects(NEOs), 2017VR12, Camillo, and Midas
during the year 2018. The observations were made by the 1-m telescope of Yunnan
Observatory over 2 nights. Their precise astrometric positions are derived from
989 CCD observations. The theoretical positions of asteroids are retrieved from
the Jet Propulsion Laboratory (JPL) Horizons System and Institut de
M\'{e}canique C\'{e}leste et de Calcul des \'{E}ph\'{e}m\'{e}rides (IMCCE). The
positions of three asteroids are measured with respect to the stars in Gaia DR2
star catalogue. For 2017 VR12, the mean (O-C) of right ascension and
declination are -0.090$^{''}$ and -0.623$^{''}$ based on the ephemeris of
published JPL, but the mean (O-C) are 3.122$^{''}$ and -0.636$^{''}$ based on
the ephemeris of published IMCCE. The great difference in declination could be
explained by several factors. (1)The degenerated CCD images caused by the high
apparent motion speed of the object leads to the reduction of positioning
accuracy. (2)The poor timing system may bring the system error, especially in
the high speed direction. (3)The asteroid may be perturbed by the earth when it
approaches the earth too closely. The astrometric results show that the
centroid centring method can reduce the dispersion of the non-Gaussian images
compared with the PSF model method. For Camillo and Midas, the astrometric
results are consistent based on two ephemerides. High-precision timing system,
some astronomical effects and geometric distortion of CCD images should be
carefully considered in the future works.
