Using the Shot Alignment Tool

A Note on Visibility vs. Shot Alignment

The Visibility and Shot Alignment tools are separate things for distinct purposes. Because they share many of the same inputs, they are grouped together on a single panel in the right-hand sidebar.

• Visibility: this tool shows where the selected body/target (e.g. the Moon) can be viewed above the local landscape at the selected time. The hatched shaded area shown in the color of the selected body indicates that there is no clear line of sight from that location
• Shot Alignment: this is a more complex tool intended to be used when you specifically wish to align a body/target (e.g. the eclipsed Sun or a nebula) relative to a specific landmark. The tool shows a heatmap that indicates where the camera could be positioned in a specified time window to achieve the required alignment

This article discusses the Shot Alignment tool.

Shot Alignment Use Cases

Here are some examples of when you might wish to use the Shot Alignment tool – click the links to view the scenario directly in TPE:

• Where can I stand to photograph Diamond Mt. Fuji at sunset in January? Scenario
• Where can I shoot September’s Full Moon rising behind the Mount Lick Observatory? Scenario
• Are there viable locations to make a deepscape of the Great Orion Nebula composed alongside Factory Butte, Utah? Scenario

When Should I Use Shot Alignment?

The Shot Alignment tool is intended to solve the reverse shot alignment problem.

The standard “ forward ” shot alignment problem is well supported in TPE and other planning tools. This is when you decide where you’ll stand, and what you’d like to compose in the shot, for example, the Moon and a landmark, and then try to identify times when the alignment occurs. Visual Search in TPE accomplishes this task, which is sometimes also known as “ position search ”.

But often, you care less about exactly where the camera is and much more about having your subject and in-frame celestial target composed correctly. If you have to move your shooting position to achieve that, fine.

The problem is that, without a tool such as Shot Alignment, you can end up “ pin hunting ”, i.e., moving the map pin around repeatedly to try to find potential shooting locations that still achieve the desired composition. Additionally, given that celestial targets move in both azimuth and altitude over time, there can be a lot of chasing back and forth.

That’s exactly when you should turn first to the Shot Alignment tool.

What Does Shot Alignment Do?

Given a date, time, and location plus a selected celestial target (Sun, Moon, Planet, Galactic Center, DSO, Star, etc.), Shot Alignment will show you directly on the map where you could in principle stand with a camera to achieve an alignment from the camera to the landmark (map pin location) and the target. The alignment is shown as a colored “ heatmap ” that shows where and when good alignments are possible. The heatmap is line-of-sight aware: if there’s no clear line of sight from a point to the landmark, the point is not shown in the heatmap.

Important: use the heatmap as a planning guide only. Indicated areas may not be safe, legal, or practical to access.

Be Sure to Experiment

One of the major advantages of this tool is that the visual output – the heatmap – updates in real time as you adjust parameters. That makes experimentation a breeze. By far the best way to understand the tool is to experiment with it and see how changing the inputs affects what you see on the map.

What User Input Is Required?

You must select a celestial target. Whichever Bodies/Targets you have selected are shown, with their corresponding map legend color. Here, we have the Sun, the Moon, and M42 (Great Orion Nebula) loaded on the map, and M42 is selected as the celestial target for use with the Shot Alignment tool:

You can optionally specify an azimuth and altitude offset, for example, to place the Moon above and to the left of the landmark – this is important when you have a specific composition in mind. Beyond that, there are several other settings that will fine-tune the tool results:

• Camera Height Above Ground Level: this is separate from the primary pin height above ground level, and defaults to ~5 feet
• Angular Tolerance: this determines how tolerant you are of misalignment between landmark and celestial target – adjust according to your photographic goals (e.g. tight, 0.25°, for the Moon directly atop a skyscraper, loose, 2°–3° for a large nebula near a prominent mountain summit)
• Time Window: this determines the duration of the time window in minutes, plus/minus, relative to the app’s selected date and time – more on this below
• Maximum Distance: this governs how far from the map pin the tool will show the alignment heatmap output. The greatest supported distance is a generous 184 miles, much longer than the vast majority of viable shots. You may enjoy better sightline resolution with a smaller distance selected
• Samples: this is the number of position samples supplied to the tool from celestial object calculations. Usually, the default is fine. If you observe any banding in the heatmap in circumstances where it covers a very large geographical area, consider increasing this. Higher values have a greater performance impact on your computer
• Opacity: the opacity of the heatmap as shown on the map

Understanding Angular Tolerance and Time Window

If you set Angular Tolerance to a very small value, say 0.1°, and the time window duration to ±1 minute, the Shot Alignment tool might show just a small colored dot on the map, see here near the top left of the image:

If you increase the Angular Tolerance to 1.0°, the alignment heatmap area increases markedly in size:

If you then increase the Window duration to ±20 minutes, the alignment zone is smeared across the map, reflecting the change in the target’s azimuth and altitude over that period:

By allowing some tolerance in these parameters, you gain the benefit of seeing how the locus of potential shooting locations evolves over time. That allows much more effective assessment by focusing your planning work on only viable locations.

Time Mode

All the discussion so far relates to the Align Mode, but another mode is available: Time Mode:

In Time Mode, the heatmap changes appearance to indicate when the alignment occurs within the given time window:

The central yellow band indicates the zone of “ good ” alignment (in tolerance). The blue area shows alignments that occur earlier in the time window. Red shows alignments that occur later in the time window. The white transition zone occurs near or at the selected time, at the middle of the window. Remember: this is all relative to whichever date/time you have selected – and you can adjust that on the fly to watch the heatmap respond in real time.

Time Mode is especially useful when shooting during twilight or golden hour when light conditions are changing quickly. For example, if you’re shooting a rising Moon near sunset, knowing which alignments are early versus those that are late helps guide your choice, as contrast may become more challenging later in the window as skies darken.

Choosing an Alignment

It’s usually easier to start using Shot Alignment with geodetics OFF. The alignment heatmap will be shown relative to the primary map pin (red), i.e. you should place the red map pin on the landmark that will be included in your shot.

You can inspect a potential shooting alignment by clicking on the map, for example:

Here, the camera would be positioned near a marked trail. The alignment occurs earlier in the selected window, as shown in the timeline bar in the inspector. The position tolerance is good – within our acceptable window. Click Select alignment to proceed.

Selecting an Alignment

First, note that you can change this easily after your first selection, so don’t worry about trying something out! When you select an alignment, the following things happen:

1. The primary pin moves to the selected alignment coordinates
2. Geodetics is enabled, and the secondary pin is placed on the landmark (the previous primary pin position if it was not enabled before)
3. The selected date/time is changed to the instant of the selected alignment
4. Note that the heatmap is drawn relative to the secondary map pin (geodetics pin, gray) when geodetics is enabled

You can then inspect the alignment using other tools, such as the geodetics sightline chart. We recommend checking the result carefully, particularly if your tolerances are tight.

Modifying the Alignment

After choosing an initial alignment, if it proves impossible (e.g. the location is not reachable by foot, or is unsafe or on private ground), you can keep clicking on the heatmap to inspect other potential alignments. Click Select alignment as often as needed – it will update the app state as needed to show you the moment and circumstances.