Understanding Azimuth, Altitude, Elevation, and Other TPE Terms

Many of the planning tools in The Photographer’s Ephemeris use terms related to direction, height, terrain, and visibility. While some of these may already be familiar, others have a more specific meaning in TPE.

This glossary explains how these terms are used throughout the TPE Help Center. Where appropriate, you’ll also find links to more detailed articles that explore each concept in greater depth.

Azimuth, Bearings, and Coordinates

These terms describe where something is relative to your chosen location. They’re used throughout TPE to calculate the position of the Sun, Moon, Milky Way, celestial targets, and other locations on the map.

Azimuth

Azimuth is a compass direction measured clockwise from true north. In TPE, azimuth tells you the direction of the Sun, Moon, Milky Way, another celestial target, or another location from your chosen viewpoint.

For example:

0° is due north
90° is due east
180° is due south
270° is due west

If the Sun has an azimuth of 250°, it appears west-southwest of your location. Likewise, if a mountain summit lies at an azimuth of 250°, the Sun and the summit will appear in approximately the same direction.

By default, TPE measures azimuth from true north. TPE Web can also display azimuths relative to magnetic north when working with an uncompensated magnetic compass.

Bearing

A bearing is the direction from one location to another.

In TPE, you’ll most often encounter bearings when using Geodetics. The bearing describes the direction from the primary pin to the secondary pin, helping you compare your camera position with a distant subject or another point on the map.

Bearings are measured in the same way as azimuths, but they describe something different. An azimuth usually describes the direction of a celestial body or another target from your location, while a bearing describes the direction between two locations.

Latitude

Latitude measures how far north or south a location is from the Equator. It’s expressed in degrees, ranging from 90° S at the South Pole to 90° N at the North Pole. In TPE, latitude is one half of a location’s coordinates. Together with longitude, it identifies a precise point on the Earth’s surface.

Longitude

Longitude measures how far east or west a location is from the Prime Meridian, which passes through Greenwich, England. It’s expressed in degrees, ranging from 180° W to 180° E. In TPE, longitude is the second half of a location’s coordinates. Together with latitude, it identifies a precise location on the map.

Coordinates

Coordinates are a pair of numbers consisting of latitude and longitude that identify a precise location on the Earth’s surface. TPE supports several common coordinate formats, allowing you to enter, copy, or share locations with a high degree of accuracy.

True north

True north is the direction toward the Earth’s geographic North Pole. By default, TPE measures azimuths and bearings relative to true north. Using a consistent reference ensures calculations remain accurate regardless of where you are in the world.

If you’re navigating with a traditional magnetic compass, you may prefer to display directions relative to magnetic north instead.

Magnetic north & magnetic declination

A magnetic compass points toward magnetic north, not true north. The angle between the two is called magnetic declination, and it varies depending on where you are.

By default, TPE displays azimuths and bearings relative to true north. TPE Web can instead display them relative to magnetic north, making it easier to compare TPE’s calculations with an uncompensated magnetic compass in the field.

Altitude, Elevation, and Terrain

When planning a photograph, it’s important to distinguish between the physical height of the landscape and how high something appears from your viewpoint. TPE uses several related terms to describe these different concepts.

Altitude

Altitude is the angle between the horizon and an object, measured in degrees.

In TPE, altitude describes how high the Sun, Moon, a celestial target, or even a distant mountain appears from your chosen location. An object on the horizon has an altitude of 0°. Objects above the horizon have a positive altitude, while objects below the horizon have a negative altitude.

Don’t confuse altitude with elevation. Elevation is a physical height above sea level, while altitude is an angle above or below the horizon.

Apparent altitude

Apparent altitude is the observed altitude of a distant object after accounting for the curvature of the Earth and atmospheric refraction.

This calculation becomes especially useful when planning alignments between the Sun or Moon and a distant landscape feature. Comparing the apparent altitude of a mountain with the altitude of the Moon, for example, helps determine whether the Moon will clear the summit or remain hidden behind it.

Elevation

Elevation is the physical height of a location above mean sea level, usually measured in feet or meters. TPE uses elevation data to calculate terrain profiles, sightlines, and the apparent height of distant landscape features.

Unlike altitude, which is an angle, elevation is a physical measurement of height.

Elevation offset

An elevation offset adds or subtracts height from the mapped ground elevation at the primary or secondary pin.

This can be useful when your camera is positioned above the ground, such as on a tripod, in a building, or on a drone. Likewise, you can use an elevation offset to represent the height of a building, tower, or other subject above the surrounding terrain.

Elevation offsets affect TPE’s calculations without changing the underlying terrain data.

Horizon

In astronomy, the horizon is the reference line where the Earth and sky appear to meet. TPE uses this theoretical horizon when calculating events such as sunrise, sunset, moonrise, and moonset.

In the real world, your visible horizon is often formed by hills, mountains, buildings, or other terrain. These features can delay sunrise, hasten sunset, or hide the Moon and other celestial targets, even though they have already risen above the theoretical horizon.

TPE includes several tools – including Geodetics, Sightline Analysis, and Horizon Profiles – to help you understand how the local landscape affects what you’ll actually see.

See also: Sunrise (etc.) is incorrect

Horizon Profile

A Horizon Profile shows the height of the surrounding terrain in every direction from the primary pin.

Unlike a single sightline, which analyzes the terrain between two locations, a Horizon Profile provides a 360° view of your local horizon. It helps you quickly identify where hills, mountains, or other terrain rise above the theoretical horizon and how they may affect the visibility of the Sun, Moon, Milky Way, and other celestial targets.

Horizon Profiles are calculated from terrain elevation data and do not account for trees, buildings, or other above-ground objects.

Geodetics, Sightlines, and Landscape Visibility

Many of TPE’s advanced planning tools compare two locations or analyze how terrain affects visibility. These concepts build on the position and height terms described above.

Geodetics

The term geodetics comes from the field of geodesy, the science of measuring and representing the Earth. In TPE, geodetic calculations take the Earth’s shape into account when measuring the relationship between two locations.

Using the primary pin and secondary pin, TPE can calculate information such as distance, bearing, elevation difference, and apparent altitude. These calculations help answer practical questions such as whether the Moon will clear a mountain ridge or whether terrain will obstruct your view.

Primary pin

The primary pin represents your main point of reference. Most calculations in TPE – including the positions of the Sun, Moon, celestial targets, and terrain analysis – are made relative to the primary pin. In many situations, it represents your planned camera location.

Secondary pin

The secondary pin marks a second location on the map. When used with Geodetics, it often represents a distant subject, landmark, or point of interest that you want to compare with the primary pin.

Sightline

A sightline is the direct line of sight between an observer and a subject.

In TPE, the sightline runs between the primary pin and the secondary pin. TPE analyzes the terrain along this line to help determine whether hills, ridges, or other landscape features obstruct the view between the two locations.

Viewshed

A viewshed is the area that can be seen from a particular observation point. Viewshed analysis is commonly used in mapping and geographic information systems to determine which parts of the surrounding terrain are visible and which are hidden.

In TPE, the Viewshed tool shows terrain visibility in every direction from the primary pin. This can help you identify possible viewpoints, understand where surrounding terrain obstructs the view, and explore where a terrestrial or celestial subject may be visible.

Because the calculation is based on terrain elevation data, it does not normally account for trees, buildings, or other above-ground objects.