Low graze angle imaging

A city seen from a satellite through an orthographic camera. Drag to pan. With an instrument selected, scroll or pinch magnifies the image like an imagery viewer; resolution is set by the optics and the slant range. Moving the angle sliders takes manual control.

Buildings and heights from Overture Maps, roads, parks, water and rail from OpenStreetMap, fetched live. Larger areas take longer.

Satellite pass

Circular orbit over a spherical earth, earth rotation ignored. The sensor stays pointed at the scene. Pass limits are where the graze angle drops to 8°.

Sensor geometry
Traffic

The detector runs twice a second. Each vehicle is found with a probability set by its size in sensor pixels, the blur, and its contrast against the road; positions carry sub-pixel to pixel noise. A track is confirmed after 3 detections in 5 frames, coasts (dashed) through misses and is dropped after 4 in a row; a reacquired vehicle gets a new id.

Cars follow the road network in real time, keep a gap to the car ahead, stop at red signals and brake before turns so sideways acceleration stays near 2.5 m/s². The button also pauses the moving ship.

Sun

In optical imagery, shadow length depends on sun elevation, not on the sensor graze angle.

Image chain

Colour is pan-sharpened the way commercial products are: red, green and blue bands with 4× the pan pixel are fused with the pan band, so colour bleeds slightly past sharp edges.

Haze scales with the slant path length, 1/sin(graze).

Rendering