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We present the results of PSR$\pi$, a large astrometric project targetingradio pulsars using the Very Long Baseline Array (VLBA). From our astrometricdatabase of 60 pulsars, we have obtained parallax-based distance measurementsfor all but 3, with a parallax precision of typically 40 $\mu$as andapproaching 10 $\mu$as in the best cases. Our full sample doubles the number ofradio pulsars with a reliable ($\gtrsim$5$\sigma$) model-independent distanceconstraint. Importantly, many of the newly measured pulsars are well outsidethe solar neighbourhood, and so PSR$\pi$ brings a near-tenfold increase in thenumber of pulsars with a reliable model-independent distance at $d>2$ kpc.Using our sample along with previously published results, we show that even themost recent models of the Galactic electron density distribution model containsignificant shortcomings, particularly at high Galactic latitudes. Whencomparing our results to pulsar timing, two of the four millisecond pulsars inour sample exhibit significant discrepancies in the estimates of proper motionobtained by at least one pulsar timing array. With additional VLBI observationsto improve the absolute positional accuracy of our reference sources and anexpansion of the number of millisecond pulsars, we will be able to extend thecomparison of proper motion discrepancies to a larger sample of pulsarreference positions, which will provide a much more sensitive test of theapplicability of the solar system ephemerides used for pulsar timing. Finally,we use our large sample to estimate the typical accuracy attainable fordifferential astrometry with the VLBA when observing pulsars, showing that forsufficiently bright targets observed 8 times over 18 months, a parallaxuncertainty of 4 $\mu$as per arcminute of separation between the pulsar andcalibrator can be expected.

Microarcsecond VLBI pulsar astrometry with PSR$\pi$ II. parallax distances for 57 pulsars