Skychart

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====== Projection comparison ======

===== Large field of view =====
The larger field of vision make the more visual difference between the different projection.\\
The example show a field of 150° and 360° wide using the different options available in the menu [[chart_coordinates|Setup -> Chart, Coordinates]]
==== MER, Mercator ====
150° FOV, standard and oblique :\\
{{:en:documentation:mer.png?300|Mercator standard}}
{{:en:documentation:merobl.png?300|Mercator oblique}}

360° FOV, standard and oblique :\\
{{:en:documentation:mer360.png?300|Mercator standard}}
{{:en:documentation:mer360obl.png?300|Mercator oblique}}

==== HAI, Hammer-Aitoff ====

150° FOV, standard and oblique :\\
{{:en:documentation:hai.png?300|Hammer-Aitoff standard}}
{{:en:documentation:haiobl.png?300|Hammer-Aitoff oblique}}

360° FOV, standard and oblique :\\
{{:en:documentation:hai360.png?300|Hammer-Aitoff standard}}
{{:en:documentation:hai360obl.png?300|Hammer-Aitoff oblique}}

==== CAR, Cartesian ====
150° FOV, standard and oblique :\\
{{:en:documentation:car.png?300|Cartesian standard}}
{{:en:documentation:carobl.png?300|Cartesian oblique}}

360° FOV, standard and oblique :\\
{{:en:documentation:car360.png?300|Cartesian standard}}
{{:en:documentation:car360obl.png?300|Cartesian oblique}}

==== ARC, full sky ====
When you click the "Show all sky" button{{:en:documentation:i42.png|}} the projection automatically change to the ARC full sky show below.\\
This same change of projection occur if you use simultaneously: an oblique projection, an azimuthal coordinate system, a very wide field of vision, and the altitude at the chart center is greater than 45°. \\
It return to your selected  projection if you zoom in or move the chart center nearer the horizon.

{{:en:documentation:arcfull.png?300|}}


===== Small field of view =====
On smaller field of vision the difference between the projections is more subtle but important if you want to match a specific image. \\
The example here show a FOV of 70° to make some difference visible at this scale, look at the grid curvature for more evidence.

==== TAN, Gnomonic  ====
70° FOV :\\
{{:en:documentation:tan70.png|}}

==== ARC, Zenithal equidistant ====
70° FOV :\\
{{:en:documentation:arc70.png|}}

==== SIN, Slant orthographic ====
70° FOV :\\
{{:en:documentation:sin70.png|}}

==== MER, Mercator ====
70° FOV, oblique :\\
{{:en:documentation:mer70.png|}}

==== HAI, Hammer-Aitoff ====
70° FOV, oblique :\\
{{:en:documentation:hai70.png|}}

==== CAR, Cartesian ====
70° FOV, oblique :\\
{{:en:documentation:car70.png|}}