Like described in the header, In short I'm wondering what the default (X,Y) coordinate order conventions are in FME (particularly in relation to the 'Lat/Long vs Long/Lat discussion')?
Reason/motivation of the question
The reason I'm asking is that in quite some workspaces I prompt users to enter an extent for a particular area (mainly to filter out data for the user defined area). Recently a user asked me if it was possible to incorporate an option to also allow the input extent to be entered by means of explicit Bounding Box (BBOX) coordinates in the form of a specific envelope, i.e. to enter both the (Xmin, Ymin) AND the (Xmax, Ymax) coordinates.
Of course these explicit coordinates are meaningless without knowing how to interpret them (i.e. without knowing the underlying coordinate system). In the Netherlands it turns out that the vast majority of spatial files make use of the 'RDNew coordinate system' (EPSG:28992). However, I also wanted to give users the option to enter coordinates that they find in google maps, which makes use of the 'LL-WGS84 coordinate system' (EPSG:4326).
Lat/Long vs Long/Lat discussion
It is at this point in time that I stumbled upon the 'Lat/Long vs Long/Lat discussion'. For more info on this I found a suggested link in the Documentation of CoordinateSwapper transformer. Unfortunately, this underlying page was no longer online, but using the Internet Archive: Wayback Machine, I managed to open a http://gisconsultancy.com/blog/microsoft/what%E2%80%99s-your-lat-long" target="_blank">stored version of this particular link. Some particular information here I found that:
"The problem seems to stem from the widely held assumption that ‘What is your Lat Long?’ is the same question as ‘What is your XY?’
However, Latitude is a measure of distance from the equator, so it’s really more analogous to the distance Y in a planar model; likewise, Longitude is a measure of distance from the Prime Meridian and is therefore analogous to the distance X in a planar model. So ‘What is your XY?’ in a flat earth model, is really more comparable to the question ‘What is your Long Lat?’ in a round earth model. "
Lastly, while I was dealing with this issue/discrepancy I also read the following page of gisgeography that seems te explain that this is the 'most natural coordinate order':
"lines of longitude have X-coordinates between -180 and +180 degrees" and "lines of latitudes have Y-values that are between -90 and +90 degrees"
So in short, it seems that the most natural coordinate order convention would be (X,Y):= (Longitude, Latitude). Fortunately this is also the order that seems to be used by FME. Unfortunately it seems that different applications make use of different coordinate order conventions, and e.g. google (at least in google maps) seems to make use of the unnatural coordinate order convention (X,Y):= (Latitude, Longitude) (see also example in comments to this item to the reply of redgeographics).
'Discrepancy' in the definitions of the coordinate order between different applications; (X,Y):= (Longitude, Latitude) (in the above claimed as the 'natural definition') OR (Y,X):= (Latitude, Longitude)
When I was working on my particular workspace I seemed to have found that there is a discrepancy in the coordinate order definition of FME and Google Maps. In short FME seems to use the 'natural coordinate order definition' (X,Y):= (Longitude, Latitude), whereas Google Maps uses the 'unnatural coordinate order definition' (X,Y):= (Latitude, Longitude). See also the example I specified at one of the comments below this item (from redgeographics).
Main question and subquestion
This all led me to the main question; What is/are the default (X,Y) coordinate order conventions in FME?
One particular subquestion I'm having is whether all of the predefined coordinate systems in FME that make use of the 'LL projection' are making use of the 'natural coordinate order definition' of (X,Y):= (Longitude, Latitude).
More confusion; my own search for an answer to the subquestion
On a first try to answer the above subquestion myself, I found the 'coordsys.db' file in the FME installation folder (as described in the FME Coordinate Systems documentation, n.b. the file actually turns out to be a CSV file that makes use of '|' as its delimiter (and without a header). What I found is that quite many of the coordinate systems that make use of the LL Projection, have some tag of 'Latitude/Longitude' in its description. See also below;
However, to add to the confusion, as described above (and below in a comment to redgeographics), it seems that mentioning 'Latitude/Longitude' is just common practice in how to speak about LL coordinates, whereas FME actually handles the first (i.e. X) coordinate as the Longtitude, and the second (i.e. Y) coordinate as the Latitude.
What I don't know however is whether this is true for all of the predefined coordinate systems in FME that make use of the LL projection, or just for my testcase where I made use of the 'LL-WGS84 coordinate system' (EPSG:4326). It would be nice if this can be verified/confirmed.
My current idea for a workaround
If it is true that the FME engine has a fixed build in structure for the coordinate order convention (as I strongly expect), it will be easier for me to know for which of the specified coordinate systems it is neccessary to apply the CoordinateSwapper transformer before using the 2DBoxReplacer transformer, and for which of the transformers this isn't neccessary.
Right now I request users to enter the BBOX coordinate envelope in the coordinate order convention (X,Y):= (Longitude, Latitude) (in case of a LL projected coordinate system). If in short the answer to my subquestion is 'Yes', I may for instance assume to always the swap coordinates when the specified coordinate system is of the 'LL projection' kind, and to keep the original coordinate order in any other case. N.b. based on the units of the predefined coordinate systems in FME, it seems a valid assumption that (nearly) all non LL projected coordinate systems will be of the 'Orthogonal (X,Y)' kind: