Editing 2170: Coordinate Precision
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The sixth entry in the table, with seven digits of precision, includes the caveat that, while your coordinates map to areas small enough on the Earth's surface to indicate pointing to a specific person in a room, "since you didn't include datum information, we can't tell who". This is a reference to the ''{{w|geodetic datum}}'' or ''geodetic system'' — different ways of dealing with the fact that the Earth is neither perfectly spherical nor perfectly an oblate ellipsoid. The various datums do not make much difference at six digits of precision, but at seven, there is enough skew depending on which system is in use that the person in a room you are referring to with the coordinates is ambiguous. It is unstated, but the remaining lines in the table with ever-greater precision suffer from this same issue and are equally ambiguous without datum information. | The sixth entry in the table, with seven digits of precision, includes the caveat that, while your coordinates map to areas small enough on the Earth's surface to indicate pointing to a specific person in a room, "since you didn't include datum information, we can't tell who". This is a reference to the ''{{w|geodetic datum}}'' or ''geodetic system'' — different ways of dealing with the fact that the Earth is neither perfectly spherical nor perfectly an oblate ellipsoid. The various datums do not make much difference at six digits of precision, but at seven, there is enough skew depending on which system is in use that the person in a room you are referring to with the coordinates is ambiguous. It is unstated, but the remaining lines in the table with ever-greater precision suffer from this same issue and are equally ambiguous without datum information. | ||
| − | The final entry, with seventeen digits of precision, suggests that either the user is referring to individual atoms in the much-larger-scale whole-Earth coordinate system, or (perhaps more likely) has not bothered to format the values from the GPS module for viewing in the software UI in any way whatsoever, resulting in a value that is {{w|False precision|meaninglessly precise}} because the measurement wasn't that {{w|Accuracy and precision|accurate}} to begin with | + | The final entry, with seventeen digits of precision, suggests that either the user is referring to individual atoms in the much-larger-scale whole-Earth coordinate system, or (perhaps more likely) has not bothered to format the values from the GPS module for viewing in the software UI in any way whatsoever, resulting in a value that is {{w|False precision|meaninglessly precise}} because the measurement wasn't that {{w|Accuracy and precision|accurate}} to begin with. Even if the value is accurate, locating individual atoms by coordinates is not actually useful in most cases, and the motions of multiple systems within our physical world (continental drift, subtle vibrations, {{w|Brownian motion}}, etc.) would render the precise value obsolete rather quickly. |
For the decimal places past the 5th on the latitude, the digits given are actually the first part of the decimal expansion of the constant ''e'' (2.7182818284), while for the decimal places past the 5th on the longitude, the digits given are part of the decimal expansion of the constant ''π'' (3.14159265358) starting with the second digit (4). | For the decimal places past the 5th on the latitude, the digits given are actually the first part of the decimal expansion of the constant ''e'' (2.7182818284), while for the decimal places past the 5th on the longitude, the digits given are part of the decimal expansion of the constant ''π'' (3.14159265358) starting with the second digit (4). | ||
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| The [https://www.kennedyspacecenter.com/-/media/DNC/KSCVC/Blog-Images/Rocket-Garden/rocket-garden-with-labels.ashx?h=860&w=1173&la=en&hash=7B9ADC7AFF5370E462AC98D9651945B806B77B2C Thor-Delta] rocket in Rocket Garden | | The [https://www.kennedyspacecenter.com/-/media/DNC/KSCVC/Blog-Images/Rocket-Garden/rocket-garden-with-labels.ashx?h=860&w=1173&la=en&hash=7B9ADC7AFF5370E462AC98D9651945B806B77B2C Thor-Delta] rocket in Rocket Garden | ||
| As the comic notes, the differences between {{w|geodetic datum}}s – different ways to map geodetic coordinates to specific points on the Earth's surface – become large enough that one needs to specify the one in use when supplying coordinates to this degree of precision (or greater, of course). Since the Earth is not a perfect ellipsoid, different parts of the planet conform best to ellipsoids of slightly different proportions, resulting in different coordinates for a specific location; not to mention that locally used datums have local reference points, which means that the local and global standards are slowly drifting away from each other with the tectonical plates. | | As the comic notes, the differences between {{w|geodetic datum}}s – different ways to map geodetic coordinates to specific points on the Earth's surface – become large enough that one needs to specify the one in use when supplying coordinates to this degree of precision (or greater, of course). Since the Earth is not a perfect ellipsoid, different parts of the planet conform best to ellipsoids of slightly different proportions, resulting in different coordinates for a specific location; not to mention that locally used datums have local reference points, which means that the local and global standards are slowly drifting away from each other with the tectonical plates. | ||
| − | Note that the comment in the comic concerns only the {{w|North American Datum|NAD 1983}} datum which is fairly close to the international, “one size fits all” standard {{w|WGS-84}}. Other datums may be shifted by tens or even hundreds of meters (yards), making geodetic datum specification necessary for less precise coordinates as well. | + | Note that the comment in the comic concerns only the {{w|North American Datum|NAD 1983}} datum which is fairly close to the international, “one size fits all” standard {{w|WGS-84}}. Other datums may be shifted by tens or even hundreds of meters (1.09361 yards each), making geodetic datum specification necessary for less precise coordinates as well. |
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