An important part of what consists of our Web SDK is to let users access the data behind the visualization they are watching on their computers' screen, whether it is the features rendered on screen, the extent of the features of the layer or the number of rows of the whole dataset.
So for that matter, new functions have to be added to our Layer specification. Replicating the ones that we had in CARTO-VL, we thought of adding those ones:
Layer.getViewportFeatures()
This method will return an array containing GeoJSON objects for the features that are visible within the current viewport.
Proposed usage:
const layer = new carto.viz.Layer('dataset');
layer.addTo(deckInstance);
// Get current viewport features
(await?) layer.getViewportFeatures();Depending on whether we do it with an SQL query or filtering features within a layer, we would need to add an await keyword. Both approaches have upsides and downsides.
-
Filtering the rendered feature data from our layer
This approach is based on getting features from MVTLayer, filter them by the bounds of the current viewport and returning them in our function. It is completely synchronous, so no need to await for our results, but filtering happens on client. But given that our coordinates are local coordinates we would need to convert them into WGS84 coordinates before coordinate comparison
-
Requesting rows within viewport to SQL API
This approach is much easier for us given that SQL API will perform the filtering and then we will return the rows' data in our function. The downside is that the request can take too much time depending on the data that is matched, and we will need to add an await keyword to our execution statement.
Layer.getExtent()
This method will return the bounds of our layer in the map, the coordinates of the rectangular area that encloses all layer features.
Proposed usage:
const layer = new carto.viz.Layer('dataset');
layer.addTo(deckInstance);
// Get layer extent
await layer.getExtent();Return value:
[
{ longitude: -180, latitude: 90 },
{ longitude: 180, latitude: 90 },
{ longitude: 180, latitude: -90 },
{ longitude: -180, latitude: -90 },
]To get layer's extent, we would need to request it to SQL API, so there's no discussion for this method's approach.
Layer.getNumberOfRows()
I think that was @VictorVelarde who added this method to Clubhouse's task, but I find it kind of strange to ask our layer for the number of rows. It is probably a better fit to have a .getDataset() or .getSource() method, and then request the number of rows to that object. What do you think?
Proposed usage:
const layer = new carto.viz.Layer('dataset');
layer.addTo(deckInstance);
// Get layer extent
await layer.getDataset().getNumberOfRows();
await layer.getSource().getNumberOfRows();
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