The easiest way to achieve this is to configure a custom tileLoadFunction
for the VectorTile source. That function, when it receives a 404, has to
request the tile for the next lower zoom, until it receives a 200, and call
`setFeatures` with the result. Something like this (untested):
import {getCenter} from 'ol/extent';
import MVT from 'ol/format/MVT';
const source = new VectorTileSource({
format: new MVT(),
url: 'https://my.tiles/{z}/{x}/{y}.pbf',
tileLoadFunction(tile, url) {
tile.setLoader(async (extent, resolution, projection) => {
let response = await fetch(url);
let status = response.status;
let tileCoord = tile.tileCoord;
const tileGrid = source.getTileGrid();
while (status !== 200 && tileCoord[0] > tileGrid.getMinZoom()) {
const z = tileCoord[0];
tileCoord = tileGrid.getTileCoordForCoordAndZ(
getCenter(tileGrid.getTileCoordExtent(tileCoord)), z - 1
);
response = await fetch(source.getTileUrlFunction()(tileCoord,
devicePixelRatio, projection));
}
const data = await response.arrayBuffer();
const format = tile.getFormat()
const features = format.readFeatures(data, {
extent: extent,
featureProjection: projection
});
tile.setFeatures(features);
});
}
});
I hope this helps.
Andreas.
On Tue, Aug 4, 2020 at 2:45 PM Daniel Urda <daniel.urda...@gmail.com> wrote:
> Hello,
>
> I am resending this since the mail requiring confirmation of registration
> to the mailing list went to my spam folder. Sorry if this results in a
> duplicate mail.
>
> I am trying to consume a vector tiles as provide by an ArcGIS Enterprise
> Server. I successfully managed to hijack the MapboxVector layer in order to
> display the tiles in OpenLayers (fortunately style description is more or
> less compatible with MapboxVector).
> The issue is that ESRI Vector Tile Services randomly decide to drop lower
> level tiles. Thus, if ESRI somehow decides that for a certain area level
> X+1 does not provide significantly more information than level X, tiles on
> level X+1 are not generated (requests result in 404) and the client is
> expected to display the data on level X. ArcGIS JS does have a mechanism to
> make sure it never gets 404 (making use of
> https://developers.arcgis.com/rest/services-reference/tile-map.htm ),
> however it seems to me that implementing that in OL would need significant
> effort with low benefits. Setting maxZoom on the vector tile is not really
> helpful, since better zoom levels may exist in some regions (detecting the
> max level that has tiles for all areas is cumbersome, but doable using the
> API in the provided link).
> Therefore, I was thinking I could somehow convince OL to render the tile
> at best available resolution when it gets 404s at better resolution. Any
> hint to where exactly in the code I could do that?
>
> Thanks,
> Daniel Urda
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