Support for loading offline .tif files in WorldWind Kotlin (imagery and elevation)

[rosalesKevin]

Hello,

I'm currently working with WorldWind Kotlin v1.4.0 and had a success loading GeoPackage (.gpkg) files for both imagery and elevation layers it works well for offline use.

My goal is to load offline .tif files directly into WorldWind, both for map imagery and elevation. I noticed that in WorldWind JavaScript, there was a commit mentioning added support for raw .tif elevation data. However, it is not currently supported in the Kotlin version.

Could you clarify:

• Does v1.4.0 currently support loading offline .tif files directly?
• If not, is there a recommended workflow (e.g., conversion to GeoPackage, or another supported format) to achieve offline .tif compatibility?

Thank you in advance.

[EMaksymenko]

Big TIFF files is not a very effective way to supply maps and elevations on mobile devices.

We recommend to preprocess TIFF files into any tiled database format like GeoPackage, MBTiles, RMaps via computer GIS systems like QGIS or ArcGIS and use them.

[rosalesKevin]

Thank you for your swift response and confirmation. You’re right regarding performance on mobile devices.

I followed your recommendation and converted some .tif files into a GeoPackage using QGIS. In the GeoPackage, I’m compressing two things:

1. A background raster layer containing the world map.
2. A raster layer containing elevation data (DEM).

Loading the imagery works fine: using .getImageLayers() and adding them to the WorldWindow layer works perfectly. However, when I try to load elevation with .getElevationCoverages() and then call elevationModel.addCoverage(coverage), it doesn’t seem to work.

I don’t get any exceptions or errors, just no visible result. Upon debugging, it appears to recognize the elevation layer as a TileElevationCoverage, so it seems like it’s being picked up. I’ve validated the elevation layer in the GeoPackage and it looks fine, but I’m not sure what else I can do to verify whether the data is actually being read correctly.

            val imageLayers = contentManager.getImageLayers()
            for (layer in imageLayers) {
                worldWindow.engine.layers.addLayer(layer)
            }

            try {
                val elevationLayers = contentManager.getElevationCoverages()
                for (coverage in elevationLayers) {
                    Log.d("TAG", "Found elevation layer: ${coverage.displayName}")
                    worldWindow.engine.globe.elevationModel.addCoverage(coverage)
                }
            } catch (e: Exception) {
                Log.e("TAG", "Failed loading elevation layer: $e")
            }

When I log the displayName of the elevation layer, it shows as null. I also tried validating by sampling an elevation point:

            val lat = Angle.fromDegrees(38.500)
            val lon = Angle.fromDegrees(23.0)
            val elevation = worldWindow.engine.globe.getElevation(lat, lon)
            Log.d("TAG", "Elevation at ($lat, $lon): $elevation meters")

But the values don’t seem to reflect the elevation data.

Do you have any suggestions verifying whether the elevation data is being loaded properly?

gpkg.zip
I have attached a GeoPackage that contains one of the elevation layer I am trying to load.

[rosalesKevin]

UPDATE:
Even though the elevation layer has no display name and still returns 0.0 when queried, I noticed that it actually works when viewed in 3D (I was initially testing in 2D). In 3D, the terrain clearly reflects the elevations of mountains..

I tested this with multiple GeoPackages, and they all show the same successful result: the elevation is applied correctly in 3D, and placemarks are also being positioned according to the elevation data.

[EMaksymenko]

Due to it has only the most detalliled tiles, it failed to display less detailed level data:

Add top-level tiles into your geopackage or declare only one level in level set.

[EMaksymenko]

Sorry for the late reply.
Your file contains correct elevation data format database, but it declares 5 zoom levels and have tile only for the most detailed 5th one.
You need to export it in such way, that it should have generalized tiles for all 5 layers.

[rosalesKevin]

Thank you for your detailed response regarding the GeoPackage. It turns out there was no error, the elevations are indeed loading correctly. In 3D, I can clearly see the terrain elevations, and placemarks are also taking elevation data. I’ll make sure that the elevation and zoom levels are detailed consistently.

I’d like to follow up with a question:
I have noticed that when zooming out to a far level, the GeoPackage layer disappears. The same behavior also occurs in the WorldWind tutorial. I understand this is due to the zoom levels defined in the GeoPackage, but I was wondering if there’s a workaround.. Something that would allow the layer to always remain visible regardless of zoom level, without explicitly creating zoom level 0 for the background.

I’ve already tried setting layer.maxAltitude to Double.POSITIVE_INFINITY:

for (layer in imageLayers) {
    layer.minActiveAltitude = 0.0
    layer.maxActiveAltitude = Double.POSITIVE_INFINITY
    worldWindow.engine.layers.addLayer(layer)
}

But the layer still disappears when zoomed out.

[EMaksymenko]

It will not disappear if GeoPackage will contain the first declared zoom level tiles.
Test example has the same issue - it declares zoom levels 0-16 but has no tiles in zoom level 0.

[rosalesKevin]

Okay, I see. So just to confirm, there isn’t any way on the WorldWind engine side to force visibility when zoomed out, if the GeoPackage itself doesn’t include tiles for zoom level 0?

[EMaksymenko]

Yes, you are right. It keeps visi le only the first declared zoom level. If it has no tiles than othing is visble, because system does not know which zoom level to use in this case.

[rosalesKevin]

Okay, really appreciate your fast response and support. 🙏

[rosalesKevin]

Hello @EMaksymenko ,

I would like to follow up on my earlier question. While I understand your recommendation to preprocess .tif files into a GeoPackage, I was wondering about a different approach. Such as using a third-party library to read .tif files and convert them into raw bytes, would WorldWind have any functionality to process those bytes directly and render them on the map?

Let’s also assume there would be a size limit when loading .tif files this way. Do you think this approach could still be feasible, or does preprocessing into a GeoPackage remain the best option?

[EMaksymenko]

TIFF file contains only the most detailed Zoom level. You need GeoPackage to store preprocessed top-level tiles to save battery and performance of mobile device.