CamSextant app

for Android and iOS

version 2.3 release notes - set/2019

CamSextant turns your smartphone into a celestial navigation tool.
It allows using the phone camera and accelerometer sensor to
read the altitudes of celestial objects, to be used in celestial navigation calculations,
similar to a marine sextant.

It has a perpetual nautical almanac for Sun, Moon, stars and planets
( all the so called 'navigation stars' and some more ). The celestial objects
are projected over the camera image, with names. Great for star and planet identification.

This version implements the Astronomic Position calculation (AP).
The position is automatically calculated once you have
at least two intercepts. As you add more altitudes, the AP is updated.

 

Some warnings about this App:

1- The phone electronic gyroscope is *not* a marine sextant. The altitude reading oscillates wildly. Even worst on a rocking boat. Don't expect the precision of navigation with quality marine sextant.

2- This app requires the GPS position. In this sense, it is not a self contained, complete "celestial navigation solution". Instead, you can use it to check the quality of the phone sensor readings.

The GPS position is used to show on screen celestial objects and to calculate the magnetic declination.

Using CamSextant


CamSextant app screenshot

Steps to obtain the astro position with CamSextant:

Step 1 - *Calibrate the sextant horizon* Point the phone so that the sea horizon is level
with the camera image horizontal cross hair. Click [Calibrate] button to save the horizon altitude.
This is known as the Index Error, and is subtracted from gyroscope reading.

If you can't see the sea horizon from your position, set index error to zero ( button X )
A lake opposite shore can provide a good horizon reference, if the lake is large enough.

Step 2 - Read the altitudes of at least 2 celestial objects.

Point the camera to the object and gently tap the image to save the altitude observation.
It is recommended that you read at least altitudes, to improve results.

If you are on a fixed position, you can use two or more observations of the same object,
taken at different times, even different days. For instance, take a Sun sight at 10:00 and another at 16:00

Observation of stars is sometimes difficult, because the phone camera is not
so good for dark sky and faint stars. Planets and bright stars at twilight hours are the best.

Observation of the Sun is possible, but you need to cover the camera objective with a really dark filter.

Sun observation filter


Samsung S9 with two layers of welder mask glass shade #12, for Sun observation


I recommend welder mask glass shades. Either shade #14 or two layers of shade #12.
Welder mask filters can be found in construction shops ( about $3 USD )
To secure the filter to the phone case, I used 3M double face adhesive foam.


Once you have, say, 3 altitudes, click the [=] menu button

This will open the sextant altitudes list. With some 5 clicks the Astronomical Position is
already calculated ( bottom-left in the screenshot above) The GPS sensor position is
also shown, so you can evaluate the quality of the observations.

Each altitude reading has a couple fields in the list:

Using CamSextant with a marine sextant

CamSextant can help the celestial navigator workflow. If you have a marine sextant at hand, you can use CamSextant to record your celnav observations. First, using the Settings button, disable the GPS sensor and set the Assumed Position ( your DR position)

Point the phone to the celestial object and tap the camera image to save time and altitude.

Select the new observation and click button '...'. Edit the phone sensor Altitude, using the marine sextant reading. Click Save.

When you have 2 or more observations, the Astronomical Position is available.

Average readings. Use this if you take a series of observations of the
same object and want the arithmetic averages of times and altitudes.

Also in this version:
- improved sensor response.
- Fixed the Az instability near 45 degree altitudes.

* update for iOS is available on the App Store

* update for Android is available on Google Play Store

Free app with no ads

Final note: the phone magnetometer needs calibration when started
see below


 

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(c)copr ago/19 oMAR