02 / WHY IT WORKS

Around the circle: azimuth

Azimuth is measured clockwise from north: east is 90°, south 180°, west 270°. This site uses north up and east right. Other charts can use a different viewing convention, so always read the labels before comparing plots.

Toward the center: elevation

Elevation is the angle above the local horizon. The elevation mask is a planning filter: exclude directions lower than a chosen angle. It is not a measured skyline. A building to the east can block a high satellite while an unobstructed western horizon remains usable.

03 / UNDER THE SURFACE

From intuition to a model

Projecting direction into a disk

This equidistant angular projection maps zenith to zero radius and horizon to the outer radius. Screen y grows downward, which explains the minus sign. Points are directions; the hemispherical illustration and disk share the same azimuth and elevation.

r=R 90∘−e90∘r = R\,\frac{90^{\circ}-e}{90^{\circ}}x=cx+rsin⁡Ay=cy−rcos⁡A\begin{aligned}x &= c_x+r\sin A\\y &= c_y-r\cos A\end{aligned}

A: azimuth; e: elevation; R: plot radius; cx, cy: plot center. Use radians inside trigonometric functions.

04 / A WORKED EXAMPLE

An eastern satellite at 30° elevation

Set azimuth to 90° and elevation to 30°. With R = 180, the projected radius is 120, so the point sits two-thirds of the way from the center to the eastern rim. A 15° mask retains it; a 35° mask excludes it. Its real orbit has not moved when you change the mask—only your selection has.

Return to the experiment and try it ↑

05 / PUT IT TO WORK

Try it in GNSS View

  1. Open observation settings and choose your position explicitly.
  2. Set the elevation mask, apply, and select a time on the timeline.
  3. Select a satellite and compare its azimuth, elevation and predicted visibility.
Open the observatory ↗

06 / COMMON QUESTIONS

Does the center mean the nearest satellite?

No. It means elevation 90°, directly overhead. Physical range is a separate quantity.

Why are some satellites hidden?

Check the selected systems, epoch and elevation mask. A satellite may be below the horizon or excluded by your settings.

Should I always use a high mask?

A higher mask rejects low directions but also removes observations. Compare geometry and local obstructions instead of treating one angle as universally best.

07 / FURTHER READING

An original GNSS View explanation. These references document the models, terminology and system context.

ESA Navipedia · GNSS Basic Observables ↗ESA Navipedia · Positioning Error ↗