Before heading to the field, check how many satellites will be visible at your site, the PDOP throughout the day and the best time windows to observe. GPS, GLONASS, Galileo and BeiDou, with the elevation mask you use.
1 Where will you observe?
You can also click right on the map. Your location stays on your device only: nothing is sent to us (addresses are looked up on OpenStreetMap directly from your browser).
2 When and how
Tick only the constellations your receiver tracks. Mask = minimum satellite elevation (15° is the usual; raise it near trees and buildings).
Plan
Visible satellites
DOP (lower is better)
Sky plot
Drag to see the sky at another time (or click the charts). Centre = zenith; edge = horizon; the dashed circle is the mask.
Orbits from CelesTrak (GP/TLE elements), refreshed every 12 h: 2026-10-03 10:48 (UTC−3). Plenty accurate for planning (a few km of error at 20,000 km altitude); it does not replace the receiver’s ephemeris.
How to use the plan
PDOP measures how much the satellite geometry “spreads” the position error: satellites well distributed across the sky give a low PDOP. In practice, below 2 is excellent, up to 4 is acceptable and above 6 it is better to wait. HDOP applies to the horizontal position and VDOP to the height (usually the worst of the three, which is why GNSS heights are less precise than horizontal positions).
For static or RTK surveys, use the chart to schedule occupations in the green windows and avoid DOP peaks. Real obstructions (trees, buildings, slopes) are not modelled: at such sites raise the mask or pick times with many satellites.
FAQ
What PDOP is good for surveying?
Below 2 is excellent; 2 to 4 is acceptable for most work; above 6 it is better to wait for the geometry to improve. Many receivers let you set a PDOP limit: above it they warn you or stop logging.
Which elevation mask should I use?
15° is the most common default; 10° gives more satellites, but low ones travel through more atmosphere and suffer more multipath. In urban or forested areas, 20° to 25° is usually more realistic.
Why is VDOP always larger?
Because we only see satellites above the horizon: there are no satellites “below” to balance the vertical. That is why the GNSS vertical error is typically 1.5 to 2 times the horizontal error.
Is the data current?
It uses CelesTrak’s public orbital elements, refreshed here every 12 hours. That is more than enough for daily planning: each satellite position is off by only a few kilometres, which does not noticeably change the sky plot or the DOP.
My receiver only tracks GPS and GLONASS. What now?
Untick Galileo and BeiDou: the chart and the PDOP will show only what your equipment can see. With all four constellations, PDOP is almost always below 1.5.