How it works
The page draws a scenespec scene (version 0.7 or
later) whose layers include a mesh: a vertex table, an index table and an optional face table, as
meshcore's write_scene() writes them.
Nothing here knows what the data is. It reads the view CRS, the extent and the local origin from the
scene and puts the frame round them: where the mesh is on the Earth, the graticule, and what the CRS
does to it.
Every vertex has two homes. On the map it sits where the CRS puts it, x east and y north of the local
origin. On the Earth it sits at its own longitude, latitude and height on the WGS84 ellipsoid,
Earth-centred and then turned so the origin is level. Unfold moves every vertex from one to the
other. Over a small survey they agree to a metre or so, most of it the turn between grid north and
true north; exaggerate the difference to see its shape (that turn, the scale factor, the fall of the
curved Earth below the plane). Over a continent they part by kilometres.
Colour can come from the scene (its palette over a vertex or face column) or from the distortion of
the CRS at every vertex, from PROJ's own factors (as on the Distortion page). A click gives the
triangle under the pointer and its face row, which is the way back from the picture to the data.
Open a scene by URL, or choose its scene.json and .arrows files together.
The default is a 212 m window of USGS 3DEP lidar near Juneau, Alaska (public domain), meshed with
meshcore and summarised per triangle with pointcore.