[GIS] proper succession of coordinates while specifying TopLeftCorner in TileMatrix in WMTS

coordinateswmts

While exploring various WMTS services, I've observed that sometimes x, y pair displayed in TopLeftCorner tag of TileMatrix tags defined in TileMatrixSet have succession changed to y, x.

There are at least two samples of AFAIK wrong succession. See for example:

http://mapy.geoportal.gov.pl/wss/service/WMTS/guest/wmts/TOPO?REQUEST=GetCapabilities&SERVICE=WMTS

(for EPSG:2180 TileMatrixSet and EPSG:4326 TileMatrixSet), and

http://ext-webbgis.lansstyrelsen.se/sverigeslanskarta/proxy/proxy.ashx?http://maps.lantmateriet.se/topowebb/v1/wmts?request=GetCapabilities&version=1.0.0&service=wmts

(for 3006 TileMatrixSet and WGS84 TileMatrixSet).

In the latter example, succession used in definition of TopLeftCorner:

<TopLeftCorner>8500000.000000 -1200000.000000</TopLeftCorner>

is in contradiction with definition of BoundingBox a few lines above:

<ows:BoundingBox crs="urn:ogc:def:crs:EPSG:6.3:3006">
    <LowerCorner>-1200000.000000 4305696.000000</LowerCorner>
    <UpperCorner>2994304.000000 8500000.000000</UpperCorner>
</ows:BoundingBox>

despite the fact that LowerCorner, UpperCorner and TopLeftCorner should use the same ows:PositionType definition from schemas-opengis-net-ows-1.1.0-owsCommon.xsd:

Position instances hold the coordinates of a position in a coordinate
reference system (CRS) referenced by the related "crs" attribute or
elsewhere.

I wonder how to copy with such discrepancies when processing WMTS GetCapabilities response automatically. Is this problem addressed in some way in existing software packages?

Best Answer

It seems that all WMTS service that were suspicious in my question, were right; I was wrong.

World of CRS definitions is not so simple.

Actual axis order to be used while constructing TopLeftCorner, results from CRS definition.

It has been explained e.g. at http://www.geotoolkit.org/modules/referencing/faq.html#axisOrder.

For CRS like EPSG:3857, EPSG:32633, axis order is "natural", i.e. horizontal one first, then vertical one.

For CRS like geodetic EPSG:4326, and projected EPSG:2180, EPSG:3006, axis order is "reversed", i.e. vertical one first, then horizontal one.

Despite this fact, coordinates in BoundingBox and WGS84BoundingBox are always listed in "natural" succession.

Actual order of axes can be detected by examining appropriate part of WKT representation of given CRS containing AXIS tags, e.g.:

EPSG:3857: AXIS["X",EAST],AXIS["Y",NORTH]
EPSG:32633: AXIS["Easting",EAST],AXIS["Northing",NORTH]

EAST first, then NORTH - no swapping required

EPSG:2180: AXIS["x",NORTH],AXIS["y",EAST]
EPSG:3006: AXIS["x",NORTH],AXIS["y",EAST]

NORTH first, then EAST - swapping is required

For geodetic CRS, swapping from lat, lon order to lon (horizontal), lat (vertical) is always required.

Or maybe there are other geodetic CRS that use lon, lat order? There are no AXIS tags in WKT for EPSG:4326.

Related Solutions

[GIS] Using Leaflet and Web Map Tile Service (WMTS)

I think the issue you had was because Lantmäteriet is using SWEREF 99/EPSG:3006 projection and Leaflet is using EPSG:3857. My solution was to use proj4leaflet to transform between those projections, like this:

import L from 'leaflet';
import { CRS } from 'proj4leaflet';

const apiKey = process.env.LANTMATERIET_TOKEN;

// This is the important task, where we set the map projection to EPSG:3006
const crs = new L.Proj.CRS('EPSG:3006',
  '+proj=utm +zone=33 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs',
  {
    resolutions: [
      4096, 2048, 1024, 512, 256, 128, 64, 32, 16, 8
    ],
    origin: [-1200000.000000, 8500000.000000 ],
    bounds:  L.bounds( [-1200000.000000, 8500000.000000], [4305696.000000, 2994304.000000])
  });

const map = new L.Map('map', {
  crs: crs,
  continuousWorld: true,
});

new L.TileLayer(`https://api.lantmateriet.se/open/topowebb-ccby/v1/wmts/token/${apiKey}/?service=wmts&request=GetTile&version=1.0.0&layer=topowebb&style=default&tilematrixset=3006&tilematrix={z}&tilerow={y}&tilecol={x}&format=image%2Fpng`, {
  maxZoom: 9,
  minZoom: 0,
  continuousWorld: true,
  attribution: '&copy; <a href="https://www.lantmateriet.se/en/">Lantmäteriet</a> Topografisk Webbkarta Visning, CCB',
}).addTo(map);

You can see my full example at https://github.com/kontrollanten/lantmateriet-leaflet

[GIS] MapProxy with WMTS source and reprojection

The problem was with the res-parameter. I had to calculate the scales based on the GetCapabilities. Here is a good guide how to do it properly https://lists.osgeo.org/pipermail/mapproxy/2013-August/001674.html

The final grid definition was

grid_sweden_3006:
   srs: 'EPSG:3006'
   bbox: [-1200000, 4305696, 2994304, 8500000]
   origin: nw
   res: [
     #  res            level     scale @90.7 DPI
     4096.0000000000, #  0    14628571.42857143
     2048.0000000000, #  1     7314285.71428571
     1024.0000000000, #  2     3657142.85714286
      512.0000000000, #  3     1828571.42857143
      256.0000000000, #  4      914285.71428571
      128.0000000000, #  5      457142.85714286
       64.0000000000, #  6      228571.42857143
       32.0000000000, #  7      114285.71428571
       16.0000000000, #  8       57142.85714286
        8.0000000000, #  9       28571.42857143
   ]                  # the end

Best Answer

Related Solutions

[GIS] Using Leaflet and Web Map Tile Service (WMTS)

[GIS] MapProxy with WMTS source and reprojection

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