By far, many stereo-matching techniques have been successfully proposed and applied in digital aerial photogrammetry. However, due to some problems such as large parallaxes, occlusions, geometric deformations, and repetitive patterns in convergent close range images, these methods may not be applicable to the same level of success as that of aerial imagery. In order to overcome these shortcomin...

High precision trigonometric parallaxes from the HIPPARCOS satellite and accurate metal abundances ([Fe/H], [O/Fe], and [α/Fe]) from high resolution spectroscopy for about 30 local subdwarfs have been used to derive distances and ages for a carefully selected sample of nine globular clusters. We find that HIPPARCOS parallaxes are smaller than the corresponding ground-based measurements leading,...

We are conducting a large program with the NRAO Very Long Baseline Array (VLBA) to measure trigonometric parallaxes of massive star-forming regions across the Milky Way. Here we report measurement of the parallax and proper motion of methanol masers in S 252 and G232.6+1.0. The parallax of S 252 is 0.476 ± 0.006 mas (2.10 −0.026 kpc), placing it in the Perseus spiral arm. The parallax of G232.6...

Trigonometric parallax observations made with the Hubble Space Telescope’s Fine Guidance Sensor #3 (HST FGS) of seven Hyades Cluster members in six fields of view have been analyzed along with their proper motions to determine the distance to the cluster. Knowledge of the Cluster’s convergent point and mean proper motion are critical to the derivation of the distance to the center of the cluste...

Three binary systems in the Hyades open cluster (51 Tau, V818 Tau, and θ2 Tau), with known metallicity and good Johnson photometric data are used to test the validity of three independent sets of stellar evolutionary tracks. A statistical method is described and applied to the colour-magnitude diagram of the six selected components, giving rise to χ2-contours in the metallicity–age plane. The e...

A good knowledge of both accuracy and precision of the Hipparcos parallaxes is one of the keys for their future scientific use. For this purpose, the Hipparcos preliminary parallaxes, as obtained after the processing of the first 30 months of Hipparcos data, are compared to various ground-based parallax estimates, using astrometric, photometric and spectroscopic data. In order to find unbiased ...

Hipparcos observations of open clusters provide mean cluster parallax determinations with an unprecedented accuracy. Possible biases in the Hipparcos parallaxes exhibited by other authors has been analysed and proven not to exist. A comparison of observed (V; B ? V) diagrams of the Pleiades and Praesepe with theoretical isochrones has been performed. It does not exhibit disagreement with Hippar...

Hipparcos parallaxes give new tests of the nature of δ Sct variables. For many individual stars accurate distances are now available, i.e. directly determined luminosities and radii can be used to test theoretical models. Of particular interest are the at present very unclear relations between high–amplitude δ Sct stars and the much more abundant low–amplitude δ Sct variables, and the relations...

We report astrometric parallaxes for three well-known dwarf novae obtained using the Fine Guidance Sensors on the Hubble Space Telescope (HST). We found a parallax for SS Aurigae of mas, for p 5 5.00 5 0.64 SS Cygni we found mas, and for U Geminorum we obtained mas. These p 5 6.02 5 0.46 p 5 10.37 5 0.50 represent the first true trigonometric parallaxes of any dwarf novae. We briefly compare th...