change x and y to ii and jj in input@axis values

[joanma747]

Can we change x and y in input@axis values?

Reason. Mathematical formulation of projection usually reserve to "x" and "y" for projected coordinates.
See, for example: https://proj4.org/operations/projections/merc.html but there are many more.

I would like to have ii and jj to suggest that they are in "pixels" and not in projected coordinates. We cannot use "i" and "j" because they are already taken.

If accepted, remember to change accordingly the "5 Examples" useful diagram

[prushforth]

Currently, the concept of TCRS is created to encapsulate the discussion of coordinate systems in web maps, such that it should be natural to discuss how the client coordinate system is related to the various coordinate reference systems that arise in discussions. Scalable Vector Graphics and Cascading Style Sheets have created the "x" and "y" terminology and coordinate system definitions that we need to work with. This terminology exists also in Leaflet. As such I don't think it wise to attempt to change from that terminology.

[joanma747]

In MapML, x,y are associated with "pixel" coordinates with origin in the top left corner of the tiled space. are associated with tcrs. SVG does not have a tiled space, CSS does not have tiled space.
Leaflet uses x,y twice in here: https://leafletjs.com/reference-1.3.4.html. The first one in the URL template. In this case x,y are tilematrix coordinates (tilecol and tilerow). The second time it is map coordinates (with origin in the map extent). Non of them are tcrs coordinates with origin in the top let corner of the tiled space.
In fact, by defining x,y with "pixel" coordinates "with origin in the top left corner of the tiled space", MapML is contradicting Leaflet, CSS and SVG.

[prushforth]

SVG does not have a tiled space, CSS does not have tiled space.

My only point is that they use axis names x and y, very specifically that the y axis is inverted from all(?) geospatial y axes and that MapML's x and y axes should be as similar as possible, in particular the axis orientation!

Leaflet uses x,y twice

Leaflet internally uses x and y per their definitions on the Web. It comes up all the time when programming with Leaflet.

Non of them are tcrs coordinates with origin in the top let corner of the tiled space.

MapML is contradicting Leaflet, CSS and SVG.

The origin of CSS and SVG coordinate systems is the top left corner. The SVG spec says:

the initial viewport coordinate system (and therefore the initial user coordinate system) must have its origin at the top/left of the viewport, with the positive x-axis pointing towards the right, the positive y-axis pointing down,

Coordinate systems in SVG are very malleable, and this is something that CRS, including TCRS don't share with SVG. But at least we can make our axis names and orientations the same.

[joanma747]

In the TCRS big table of the current version of MapML I accidentally spoted this text in the captions:
"Origin (x,y)".
The way it is used (pcrs coordinates) is i contradiction with the way x,y is defined in 'input@axis' (pixel coordinates).
May I suggest to change it to "Origin (Easting, Northing)" to eliminate possible confusions.

[prushforth]

May I suggest to change it to "Origin (Easting, Northing)" to eliminate possible confusions.

How about adding the axis name/ abbreviation to the coordinate itself? I noticed that there is 'n/a' listed under the origin of WGS84, which should be (0,0)?

We would then have E/N for the pcrs origins and lon/lat for the WGS84 origin.