KML Clamped to ground

[moisesrbd]

Hello friends
Is there any way to configure, in the init file catalog, that a KML item is drawn clamped to ground?
Cesium supports it ,but I don't know if Terria supports this type of configuration using, for example options = {} in the KML Item definition
Thanks.

[hardreddata]

You can "clampToGround":true in the catalog item. I am assuming this applies to the OGR converted layers. It is documented https://docs.terria.io/guide/connecting-to-data/catalog-type-details/geojson/ for geojson.

[moisesrbd]

HI, thanks for your answer.
I tested GeoJSON Item with clampToGround and works ok, but KML item still not working.
Im looking for something like this:
{ "name": "Vic Police (KML)", "type": "kml", "url": "test/vic_police.kml", "clampToGround" : true }

[hardreddata]

I actually struggle to understand this setting also.

I think if your data file includes an elevation component, switch to a 3D terrain map type, and if your data doesn't include a Z component, use the smooth globe.

Or maybe it is broken, or doesn't work for kml. Someone else will better be able to comment on this.

[tephenavies]

Hi @moisesrbd. Reading through KmlCatalogItem.js it looks like polygons should be clamped to the ground here whenever using 3D mode (terrain or smooth). There is no option like in GeoJsonCatalogItem to disable clamping to ground. What type of geometry do you have?

[tephenavies]

I've looked at the difference between KML and GeoJSON catalog items and I think KmlCatalogItem.js just needs to add clampToGround as a parameter (like in GeoJsonCatalogItem and tracking updates to clampToGround ). Then change the signature of every call to dataSource.load() in KmlCatalogItem starting here to pass through an options object as the second parameter:

var options = {
  sourceUri: proxyCatalogItemUrl(that, that.dataSourceUrl, "1d"),
  clampToGround: that.clampToGround
};

Here are the docs for the dataSource.load() function in Cesium. It looks like at the moment we aren't calling this with the right parameters, (possibly there was a breaking change to Cesium some time ago when clampToGround was added to Cesium).

Would you be interested in writing a PR for this change @moisesrbd?

[tephenavies]

And I think doneLoading could be removed from KmlCatalogItem too since Cesium will take care of all clamping.

[moisesrbd]

Hi Steve.
Thanks for your good answer.
Indeed, I reviewed the implementation in Terriajs v8 (next branch) and made changes to make the KML clamped.
I did not want to publish it because I consider that it is a functionality with little use. Only that I needed it in special cases that we wanted to draw the KML on a 3DTile representing an open pit, without having to give the Z coordinates of each point of the polygons.
In the case of Terria next, I added the corresponding property to KmlCatalogItemTraits and Modified KmlCatalogItem to load in the same way as GeoJSONCatalogItem.

Thank you very much again.
Best
Moises

[tephenavies]

We would welcome a PR to add clampToGround to KmlCatalogItem in next/v8. Actually I also just wrote a ticket for improvements that we should make to KmlCatalogItem in next after I wrote that answer up (thinking you were working off version 7). If you have some changes that could tick off one of those boxes that'd be great.