[sdw] CRS negotiation in MapML

prushforth has just created a new issue for https://github.com/w3c/sdw:

== CRS negotiation in MapML ==
Each MapML document has a single TCRS, which is either declared in a `<meta>` tag or by the required `<extent@units>` attribute, (if the document has the optional `<extent>` element).

When the referring `<map>` has a different declared projection (TCRS), currently the client (which in the future may be the browser) disables the layer and does not make tile/image/feature requests.

What if the MapML document was able to declare that its content was also available under a different TCRS, using one or more appropriately configured `<link rel="alternate" projection="{TCRS_NAME_HERE}" href="...">` elements?  Could (should?) the client transparently redirect to the more appropriate map resource?

    <title>Canada Base Map - Transportation (CBMT)</title>
    <meta http-equiv="Content-Type" content="text/mapml"/>
    <meta charset="utf-8"/>
    <base href="/api/beta/mapml/en/cbmtile/cbmt/"/>
    <link rel="license" href="https://www.nrcan.gc.ca/earth-sciences/geography/topographic-information/free-data-geogratis/licence/17285" title="Canada Base Map © Natural Resources Canada"/>
==> <link rel="alternate" projection="OSMTILE" href="http://geogratis.gc.ca/api/beta/mapml/en/osmtile/cbmt/"/>
    <link rel="zoomin" href="/api/beta/mapml/en/cbmtile/cbmt/?z=18" type="text/mapml"/>
    <extent units="CBMTILE" method="GET">
      <input name="z" type="zoom" value="0" min="0" max="17"/>
      <input name="projection" type="projection" value="CBMTILE"/>
      <input name="y" type="location" units="tilematrix" axis="row"/>
      <input name="x" type="location" units="tilematrix" axis="column"/>
      <template type="tile" tref="https://geoappext.nrcan.gc.ca/arcgis/rest/services/BaseMaps/CBMT3978/MapServer/tile/{z}/{y}/{x}?m4h=t"/>


More discussion [here](https://github.com/Maps4HTML/MapML/issues/11) and [here](https://github.com/w3c/sdw/issues/757).

Please view or discuss this issue at https://github.com/w3c/sdw/issues/1058 using your GitHub account

Received on Tuesday, 10 July 2018 13:22:29 UTC