The verbiage seems excessive to me. People discussing meridians, lat/long, etc. are putting too much thought into it.
Simply put, a coordinate is not a line, it's a position on a grid calculated from a set point on the grid having a determined or assumed value on a reference plane. All coordinates from that point are calculated by latitude and departure from the known or assumed values of a fixed position.
Instances you mentioned where you've seen negative coordinates being used.
Here are a selection of entries, updated thanks to your meticulousness:
northing coordinate (expressed as a distance) that defines the position of a point northwards of a reference axis in a plane coordinate system; east-west gridlines have the same northing
latitude coordinate (expressed as an angle) that defines the position of a point northwards or southwards in a geographic coordinate system
coordinate one of the values in a set of coordinates referring to one dimension of a coordinate system; it may be expressed as an angle or distance depending on the coordinate system
set of coordinates two or three coordinates that together express the position of a point; their number, order and measurement unit are specified by the coordinate system
@terminologist Thanks fot that. I finally had my BP close to normal...lol
Two comments:
Geographic coordinates. Using geographic as the adjective is very informal and not precise. A better adjective is geodetic. This term conveys the characteristic that the coordinates are rigorously determined relative to a mathematically determined spheroidal model of the earth.
Set of coordinates. This is an ambguous term. You want it to mean the numbers within the parentheses, but it usually means a group points rather than the grouping within the representation of a single point.
Perhaps "Coordinates of a Point" is what should be defined. Then it's an ordered pair or triple of numbers, each number representing the distance from a particular axis defined by the number's position in the representation.
That's a first draft, but you get the ideas that should be expressed.
@mathteacher I had been wondering about whether I should use 'geodetic' or 'geographic' when referring to a coordinate system, and I understand your point.
I guess I should therefore specify a latitude or longitude as a 'geodetic latitude' or 'geodetic longitude' too?
Following that logic, would 'ellipsoid coordinate system' be a valid term if representing the Earth's shape using only a basic ellipsoid?
I guess I should therefore specify a latitude or longitude as a 'geodetic latitude' or 'geodetic longitude' too?
Yes. It is important to specify "geodetic" when referring to latitude in particular, because that is the one that is most often used, and differs from geocentric latitude:
Following that logic, would 'ellipsoid coordinate system' be a valid term if representing the Earth's shape using only a basic ellipsoid?
I would simply call it a geodetic coordinate system or geodetic reference system - that's how they are usually referred to. Whether they use an ellipsoid or a sphere (or none at all in the case of ITRF), and what definition of either they use, are found in the details/definition of a particular system. No need to muddy the waters by adding another term.
I'm going to think out loud here, so this may get a bit wordy.
The latitude and longitude of a point can be found without reference to an ellipsoid. In the Northern Hemisphere, the altitude of Polaris is the latitude and the difference between the local time and that at Greenwich is the longitude. The determination is rigorous, but these coordinates cannot be used with other similarly determined positions for consistent surface calculations.
An ellipsoid, or even a sphere, provides a mathematically-defined surface for calculating distances and azimuths and that's the advantage it provides.
Perhaps one solution is to keep the terms latitude and longitude and incorporate the geodetic concept in the definition. Something like "...the angular measure from Greenwich to the observed point on the prescribed datum ." (have to define this, but it should be part of your work).
Now there's a bit of an understanding problem here. With a sphere, the longitude is an angle whose vertex is at the sphere's center. With an ellipsoid, the vertex of the angle is not at the center. The reason is that sides of the angle have to be perpendicular to the surface of the figure.
Using "angular measure" sidesteps this issue but doesn't account for it at all. Thus, it depends on your audience and how precise you want to be.
Since your work is coordinate oriented, I think that the ellipsoid approach is best for latitudes and longitudes.
You've taken on a tough task: good luck!
Instances you mentioned where you've seen negative coordinates being used.
Negative coordinates used to be quite common. The older guys that surveyed used them to calculate their way around. I've always assumed most of those calculation sheets I've seen were from GLO surveyors transplanted into the private world. Basically, the coordinates were Northings and Westings.
The idea was that the westing coordinates were a translation of longitudes into feet values so as you move west the coordinate gets larger as a negative number. We are quite arrogant today, those surveyors were easily surveying with Lat., Long numbers in the 1920's and 30's with no computer help. Let that sink in.
Still, anyone setting up a coordinate system can slide into negative numbers as the system expands. That's why most are careful to plan ahead and make the coordinate for the origin point large so no matter how far you go it's still positive.
You do a Lot, Block and set it up with 10,000, 10,000. You have to start finding far flung block corners so you get quite a data base. A request for a survey in the Subdivision to the south is taken up, then to the next subdivision, doesn't take long and you're into negative northings. Or you have a patchwork of different 10,000, 10,000 coordinate systems; not ideal.
Yes, or any large area coordinate system.
I haven't done a 10,000, 10,000 job in a very long time. Even during the TS days we had extensive coordinate control run most areas we worked.
