5 ms·

> GPS coordinates *coordinates There are four GNSS constellations, of which GPS is only one...... a statement that negates the fact ones position on Earth may

by GJim 2y ago

> GPS coordinates *coordinates There are four GNSS constellations, of which GPS is only one...... a statement that negates the fact ones position on Earth may be calculated using a variety of other means. EDIT: In response to replies below; One isn't questioning the coordinate system (!), rather the assumption as to how they have been calculated.

arnsholt 2y ago
In this context, it's not terribly hard to divine that they probably mean EPSG:4326 coordinates. I was going to comment that one of the ETRS89 UTM zones might be easier to work with, but on second thought the data almost certainly includes the DOMs if not the TOMs, so a global coordinate system is probably best.
- deleted 2y ago
  [deleted]
- manarth 2y ago
  The BAN provide fields `long` and `lat` which are WGS84, and also `x` and `y` which are coordinates expressed in "the appropriate local CRS" (without much elaboration on what that would be).
  - ryandrake 2y ago
    Not to mention that “latitude” and “longitude” cannot uniquely describe an address, regardless of the datum or ellipsoid. Maybe that is not the intent of storing the coordinates. Lat/Lon says nothing about floor number in a multi-story apartment.
  - willyt 2y ago
    That would be the French national grid system, no? The UK has the ordnance survey grid which is based on the OSGB36 datum. I'm pretty sure France will have a similar national datum to create their own local grid coordinates as planning and building works needs to be done in a more accurately aligned local datum than WGS84.
    - wongarsu 2y ago
      For mainland France it's reasonable to assume the French national grid. But what about French Guiana in South America or Mayotte in Southern Africa (an island north of Madagascar)? France still spans the globe, with many places treated as equals to the French mainland.
defrost 2y ago
There are many ways to calculate an earth position, sure - to name a few; triangulation from stations, LORAN, or a combination of the two with a frequency change and some moving stations such as one of the five GNSS constellations. There are many coordinate systems; these days in 2024 it is almost universal to calculate from various stations to a WGS84 position, in that coordinate system and using that geodetic datum. Back in the day, there were many datums in common use, based on a plurity of reference ellipsoids, with a multitude of pojections in common use. https://en.wikipedia.org/wiki/Earth_ellipsoid#Historical_Earth_ellipsoids https://en.wikipedia.org/wiki/Earth_ellipsoid#Historical_Ear... To this day there are several thousand indexed earth coordinate systems: https://en.wikipedia.org/wiki/EPSG_Geodetic_Parameter_Dataset https://en.wikipedia.org/wiki/EPSG_Geodetic_Parameter_Datase... https://epsg.org/home.html https://epsg.org/home.html
pjc50 2y ago
Like "Hoover", "GPS" is now a generic term for positioning systems.
- extraduder_ire 2y ago
  For Positioning Systems that are Global, anyway.
yard2010 2y ago
Fun fact: the word Νερό (nero) means water in greek. The actual meaning is fresh (I think it's the source of the word "new" too). It turns out, that many years ago you meant something else than fresh water by saying just water, so you have to be specific when you're talking about fresh water. In ancient greek water is ὕδωρ (hudr, think hydro, water) and fresh water is νεαρὸν ὕδωρ (neron hudr). Sometime in the past, the ancient Greeks were sick of saying 2 words to say water. So they dropped the second one. Something similar happens with GPS coordinates. People are just saying GPS when they mean coordinates. even though the logical thing to do is drop the GPS (neron) and just say coordinates (hudr). Personally, I think that language is just a bunch of symbols that have no real meaning. Each symbol means something only in a context, no matter how broad or specific. I would argue that it doesn't matter which word is more logical to use because logic is just a part of the context. But you are right.

by GJim 2y ago

arnsholt 2y ago

In this context, it's not terribly hard to divine that they probably mean EPSG:4326 coordinates. I was going to comment that one of the ETRS89 UTM zones might be easier to work with, but on second thought the data almost certainly includes the DOMs if not the TOMs, so a global coordinate system is probably best.

deleted 2y ago
[deleted]
manarth 2y ago
The BAN provide fields `long` and `lat` which are WGS84, and also `x` and `y` which are coordinates expressed in "the appropriate local CRS" (without much elaboration on what that would be).
- ryandrake 2y ago
  Not to mention that “latitude” and “longitude” cannot uniquely describe an address, regardless of the datum or ellipsoid. Maybe that is not the intent of storing the coordinates. Lat/Lon says nothing about floor number in a multi-story apartment.
- willyt 2y ago
  That would be the French national grid system, no? The UK has the ordnance survey grid which is based on the OSGB36 datum. I'm pretty sure France will have a similar national datum to create their own local grid coordinates as planning and building works needs to be done in a more accurately aligned local datum than WGS84.
  - wongarsu 2y ago
    For mainland France it's reasonable to assume the French national grid. But what about French Guiana in South America or Mayotte in Southern Africa (an island north of Madagascar)? France still spans the globe, with many places treated as equals to the French mainland.

defrost 2y ago

There are many ways to calculate an earth position, sure - to name a few; triangulation from stations, LORAN, or a combination of the two with a frequency change and some moving stations such as one of the five GNSS constellations. There are many coordinate systems; these days in 2024 it is almost universal to calculate from various stations to a WGS84 position, in that coordinate system and using that geodetic datum. Back in the day, there were many datums in common use, based on a plurity of reference ellipsoids, with a multitude of pojections in common use. https://en.wikipedia.org/wiki/Earth_ellipsoid#Historical_Earth_ellipsoids https://en.wikipedia.org/wiki/Earth_ellipsoid#Historical_Ear... To this day there are several thousand indexed earth coordinate systems: https://en.wikipedia.org/wiki/EPSG_Geodetic_Parameter_Dataset https://en.wikipedia.org/wiki/EPSG_Geodetic_Parameter_Datase... https://epsg.org/home.html https://epsg.org/home.html

pjc50 2y ago

Like "Hoover", "GPS" is now a generic term for positioning systems.

extraduder_ire 2y ago
For Positioning Systems that are Global, anyway.

yard2010 2y ago

Fun fact: the word Νερό (nero) means water in greek. The actual meaning is fresh (I think it's the source of the word "new" too). It turns out, that many years ago you meant something else than fresh water by saying just water, so you have to be specific when you're talking about fresh water. In ancient greek water is ὕδωρ (hudr, think hydro, water) and fresh water is νεαρὸν ὕδωρ (neron hudr). Sometime in the past, the ancient Greeks were sick of saying 2 words to say water. So they dropped the second one. Something similar happens with GPS coordinates. People are just saying GPS when they mean coordinates. even though the logical thing to do is drop the GPS (neron) and just say coordinates (hudr). Personally, I think that language is just a bunch of symbols that have no real meaning. Each symbol means something only in a context, no matter how broad or specific. I would argue that it doesn't matter which word is more logical to use because logic is just a part of the context. But you are right.