Celestial Sphere

Celestial Sphere is a web application that provides a neat and user-friendly interface for drawing and visualizing diagrams on a sphere. My aim for building this is to provide a tool for students and educators to easily learn and engage with spherical diagrams, which are commonly used in spherical astronomy.

Controls

• Left Click on the sphere to add a point.
• Left Click on a point to select/deselect it.
• Shift + Left Click to select multiple points.
• Move a point by dragging it with left mouse button while it is selected.
• Esc to deselect the selected point(s).
• Delete to remove selected point(s).
• Name a point by typing when it's selected.
• Right click another point while having a point selected to draw/remove an arc of a great circle between them.
• Scroll to zoom in/out.
• Pan while holding the middle mouse button to rotate the sphere.
• / to place a point diametrically opposite to the selected point(s).
• . to draw a great circle having the selected point as a pole.
• Shift + . to draw a great circle with the 2 selected points lying on it.
• , to draw a small circle with the 3 selected points lying on it.
• Shift + , to draw a small circle with the first selected point as the pole and second selected point as a point on the small circle.
• Shift + type to name the great circle/small circle, while the associated pole point is selected.
• Shift + move to snap a point onto a nearby great circle.
• Shift + Left click on the sphere to add a point on a nearby great circle.
• Ctrl + h to hide/show the selected point(s).
• Ctrl + g to group the selected points.
• Ctrl + u to ungroup the selected points.

Features

• The rotation of the sphere can be controlled by dragging with the middle mouse button, as well as by using the sliders.
• Coordinate grid can be turned on/off.
• The sphere can be zoomed in/out using the mouse wheel or the slider, to a minimum of 50% and a maximum of 200%.
• On having a point selected, the coordinates of the point are displayed. The point can be configured to be non-movable or non-removable.
• If a single point having an associated great circle is selected, properties of the great circle are displayed.
• If 3 points are selected, the properties of the triangle formed by them are displayed.
• Diagrams can be saved as .json files, which can be loaded later. The diagrams can also be saved as .svg files. A fresh new diagram can be obtained. These options are available at the bottom left in the file panel.
• Small circle having the same pole as a great circle can not be renamed, the great circle has to be first removed, then the small circle can be renamed.
• Points can be hidden, which will not be displayed on the sphere. This can be toggled by using the checkbox on the top left panel.
• Points can be grouped, which will allow for easier manipulation of multiple points at once. The grouped points move together, and can be renamed as a group. Ungrouping will remove the group but keep the points intact.

TODO

• Add a method to place a point at a distance from a selected point
• Add a method to place a point at an angle to selected points
• Add a method to place a point at a distance and angle from selected points
• Add a method to place point at a given coordinate.
• Add features to snap to circle intersections, small circles and arcs.
• Add feature to add multiple small circles with one pole.