Is there any ephemeris generator that gives you accurate distances between Earth and other bodies? I've tried JPL's HORIZONS ephemeris generator and while it gives accurate celestial coordinates for an object it doesn't give the geocentric distance.
JPL's Solar System Simulator gives the distance to an object at a certain time however only down to a few digits.
Is there an accurate tool that generates exact (meaning down to the meter) geocentric distances between Earth and another Solar System body over increments of time?
JPL HORIZONS gives the distance from the observer to the target as delta.
In Table Settings this option is 20. Observer range &amp; range-rate.
For asteroids and comets, it can also give distance uncertainty (39. Range &amp; range-rate 3-sigmas) as RNG_3sigma.
You can choose units of au or km.
For example, with Table Settings: QUANTITIES=1,20,39; range units=KM, the geocentric ephemeris for asteroid (153201) 2000 WO107 around its 2020-11-29 close approach to Earth looks like:
 Date__(UT)__HR:MN     R.A._____(ICRF)_____DEC            delta      deldot RNG_3sigma RNGRT_3sig

 2020-Nov-29 03:00     08 48 22.83 +14 26 33.8 4.3065970451E+06  -1.1137937   143.5915  0.0000166
 2020-Nov-29 04:00     08 43 44.11 +14 51 56.9 4.3035317776E+06  -0.5890828   144.6349  0.0000171
 2020-Nov-29 05:00     08 39 04.01 +15 17 00.3 4.3023570178E+06  -0.0635364   145.6159  0.0000175
 2020-Nov-29 06:00     08 34 22.78 +15 41 42.1 4.3030745286E+06   0.4621549   146.5331  0.0000180
 2020-Nov-29 07:00     08 29 40.62 +16 06 00.2 4.3056835832E+06   0.9872992   147.3852  0.0000185

In other words, at 05:00 UT, the asteroid is 4,302,357 ±49 km from the center of Earth.
Though its orbit is determined well enough for a permanent number designation, even 1 km precision would be unreliable.
Its perihelion distance q is only known to ±8.7 km and perihelion time tp to ±1.7 s.
New observations may improve this.
Update: new observations of (153201) 2000 WO107 improve its q to ±6.9 km, tp to ±0.3 s, and distance at 2020-11-29 05:00 UT to 4,302,522.2 ±1.1 km.
That precision is largely due to radar data, which are not always available.