Fly

3D, terrain and offline maps

Corvus can show the ground with its real shape and the buildings standing on it, with the aircraft at the height it is actually flying. All of it, map imagery, elevation and buildings, can be stored in advance for a field with no internet.

The map tilted into 3D over a 20 cm surface model: the field with its trees and the buildings around it in relief, the flown track, and the aircraft drawn above the ground at its altitude. — 3D in the blue theme over your own surface model: trees and roofs in the ground, the aircraft at its altitude.

Switching to 3D

The cube button on the map's control rail turns 3D on and off. 3D always shows the ground with its real shape wherever elevation data is available: hills are hills and valleys are valleys, drawn at true scale rather than exaggerated, with light shading so slopes read on any map style. What you are judging is clearance, and a hill drawn half again too tall is a hill you misjudge.

Rest the pointer on the cube button (or long-press it on a touch screen) and a small panel appears with two settings:

Buildings: On, buildings are extruded from OpenStreetMap footprints at their tagged heights, so the things actually in your way are in your way on screen too. Off, 3D shows the terrain alone and asks for no building data, which is the choice for a link you would rather keep for telemetry, or a laptop on battery.
Elevation: Which elevation model the terrain is drawn from; see below.

The panel only chooses; it never turns 3D on by itself, so you can set it before you press the button. The settings, and whether 3D was on, come back the next time you open Corvus.

The globe

Zoomed out, you get the Earth as a sphere with an atmosphere around its rim, which you can spin, mountains included. Zoom in and it hands over to the close view with nothing to press: from the whole planet down to the far end of the runway is one continuous movement.

Elevation models

Model	What it is
Automatic	The default. Uses the map service's own model when it has one and its key is set (MapTiler, Mapbox), and Copernicus GLO-30 otherwise. The row says which one is in use right now.
Copernicus GLO-30	The European 30 m model, noticeably sharper than SRTM on ridges and in narrow valleys, with national survey models (lidar, 1 to 10 m) where a country publishes one, for example Austria, Switzerland and parts of Germany. It is a surface model: forest and large buildings are part of the heights, which is what an aircraft has to clear. No key needed; served by the Mapterhorn project.
SRTM (AWS Terrain Tiles)	The older free model.
MapTiler Terrain, Mapbox Terrain	Appear once that service's key is set.

Whatever you pick, a tile that cannot be had (offline, or with a key refused) is filled in from the free SRTM model, so choosing a better model never gives you a worse picture. Google publishes no elevation tiles.

Your own elevation data

A survey office's surface model (a DOM or DSM, often 1 m) shows trees, buildings and masts that the 30 m models smooth away. Load it under Settings, Appearance, Elevation data and it appears in the 3D panel under Elevation like any other model.

The map tilted into 3D over a 20 cm surface model made of three DOM tiles: the field with its trees and the buildings around it in relief, a geofence along the field's edge, the flown track and the aircraft at its altitude. — Three 20 cm DOM tiles of the Neubiberg field as the elevation model: every tree is in the ground.

Formats. GeoTIFF (one band of heights, LZW, Deflate or uncompressed), XYZ text with one x y z line per grid point, and ESRI ASCII grids (.asc). Several files, such as a folder of 1 km tiles, load into one model in one go, and the add button on a model puts more files into it later.
Coordinate system. A GeoTIFF names its own. An XYZ or ASCII file does not, so choose it before loading: German state data is usually ETRS89 / UTM zone 32N (EPSG 25832). Supported are WGS 84, ETRS89 and NAD83 UTM zones, Web Mercator, DHDN Gauss-Krüger, the British National Grid, Lambert-93, LAEA Europe and the Swiss LV95 and LV03 grids. Any other system is refused with that list rather than guessed.
Served by Corvus itself. The files are converted once and kept next to the offline map cache. Corvus cuts elevation tiles from them as the map asks, so there is no separate server to run, and it works with no connection at all.
Around your data. Outside the area your files cover, the free SRTM model fills in, so the surrounding country never drops to sea level. Where SRTM is not on the laptop either (offline, never downloaded), the edge of your data is continued outward instead, so leaving your area never ends in a cliff or a blank map.

The aircraft in the scene

The aircraft flies in the scene rather than sliding along the ground. It is drawn at the altitude it is really at, with a dashed line down to a shadow on the ground directly beneath it and its height above ground beside it, so "how high am I over that ridge" is something you can see instead of work out from two numbers.

Buildings

Buildings come from OpenStreetMap through the Overpass service, in blocks of about 1.5 km. Online, a block can take a few seconds to arrive and the map keeps asking until it has it, so buildings fill in over a moment rather than all at once. A building on the edge between two blocks is drawn once.

Where a building is missing although you are online, it is usually missing from OpenStreetMap itself. A building without a height tag is drawn two storeys high.

The photorealistic 3D buildings in Google Earth are a licensed product that needs a Google API key and a different renderer, and Google does not allow them to be stored for offline use. Corvus draws real footprints at real heights, not photographed models.

Offline maps

Corvus caches every map tile it fetches into a local store, so ground you have already looked at keeps working with no connection. The store is an MBTiles database in ~/.corvus/tiles unless the config file names another folder (see where Corvus keeps its files).

Downloading an area

To prepare for a field trip, use Download offline map on the map and draw an area. The estimate shown before you commit includes everything that will be stored. Downloads are:

Named, so "what do I have offline?" can be answered by name rather than by coordinates.
Listed and drawn as outlines on the map. In the Mission planner they stay hidden until you ask for them, one box per area.
Complete for 3D by default. The elevation (the free model plus the one 3D is using) rides along, from the whole world view down to the deepest zoom you download, and so do the area's buildings.

Buildings are fetched in the background after the tiles, nearest the centre first, so leave Corvus online for a few more minutes after a large download.

Terrain with no connection

3D keeps its relief in the field with no connection, also when you zoom in further than you downloaded: finer elevation is then worked out from the coarser tiles you have, and where coarse and fine ground meet it is joined into a slope instead of a step or a crack. Beyond the downloaded area the terrain is drawn from the coarse tiles without imagery, and there are no buildings. Everything else on the map keeps working.

Panning onto ground you do not have

After a few failed lookups Corvus stops trying the network for 30 seconds, so cached tiles keep rendering at full speed and the rest stays blank rather than freezing the map. Moving back into covered ground, or getting a connection back, recovers on its own.