====== Chart, Coordinates Setting ======
From the menu: **Setup -> Chart, Coordinates**
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The Chart, Coordinates Setting has six tabs:
  * [[chart_coordinates#chart_coordinates|Chart, Coordinates]]
  * [[chart_coordinates#field_of_vision|Field of Vision]]
  * [[chart_coordinates#projection|Projection]]
  * [[chart_coordinates#object_filter|Object Filter]]
  * [[chart_coordinates#grid_spacing|Grid Spacing]]
  * [[chart_coordinates#object_list_setting|Object List Setting]]

===== Chart, Coordinates =====

==== Chart Setting ====
{{  en:documentation:chart_coordinates.jpg|}}

Here, you can specify the coordinate system used for the chart.
The four available systems are:
  * Equatorial coordinates
  * Azimuthal coordinates
  * Galactic coordinates
  * Ecliptic coordinates

==== Type of coordinates ====
//**Precession, nutation and aberation recognition**//  
Your choice here determines which type of coordinates SkyCharts will display for a selected object on  the **[[status_bar#right|status bar]]**, on the bottom of the chart.
If you don't check the **Expert mode**, you can choose in the groupbox **Type of coordinates** from four options:
  * **Apparent, true equator, equinox and epoch of the date** \\ This is the true apparent position for the equinox of date of the chart, including correction for proper motion, precession, nutation, aberration, light deflection. Normally you want this setting as this is the only to show the real position of the objects.
  * **Mean of the date, mean equator, equinox and epoch of the date** \\ The position for the equinox of date of the chart, including correction only for proper motion and precession. Use this setting only to compare the coordinates with other source that use this system, like printed almanac
  * **Mean J2000, mean equinox and epoch J2000** \\ The mean position for the date 2000.0, including correction for proper motion and precession at 2000.0. Use this setting only to compare the coordinates with other source that use this system, like printed atlas.
  * **Astrometric J2000 , mean equinox J2000 and epoch of the date** \\ Use the equinox 2000.0 and precession for 2000.0, but proper motion for the current chart date. This setting is only used to compare the coordinates with an astrometry software. 
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{{  en:documentation:chart_coordinates_expert.jpg|}}

In **Expert mode** you can specify more details :
  * **Equinox** year (from -20000 to 20000)
  * **Epoch** year (from -20000 to 20000)
  * **Proper motion** checkbox to correct positions for the given epoch
  * **Mean position** or **True position** for //Nutation// and //aberration//. 
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Fast ways to make simple changes to the chart coordination system are from the menu by **Chart -> Coordinate Sytem -> [[menuchart#coordinate_system|[Your Choice]]]**, or directly on the chart by the icons in **[[left_bar#coordinate_system_group|coordinate system group]]**.
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===== Field of Vision =====
{{  en:documentation:chart_fov.jpg|}}

Here you can specify eleven ranges as the Field of Vision (numbered from 0 to 10).

For each range you can specify the minimum FOV in degrees, which automatically will become the maximum for the preceding range.

The first range minimum is 0.0° and last range maximum is 360° (which funny enough appears as 0.0°), these values cannot be modified.

These ranges are listed at bottom of all the **[[catalog|Catalog]]** dialog box tabs and also are used with the **[[chart_coordinates#Projection|Projection]]**, **Object Filter** and **Grid spacing** tabs. 
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Changing the FOV itself can be done from the menu by **Chart -> [[menuchart#Field_of_Vision|Field of Vision]]** or directly on the chart by the icons in **[[right_bar#The_Field_of_Vison_Group|the field of vison group]]**. A very precise FOV can be manually set by the FOV part in the dialog box from the menu **View -> [[position|Field of Vision (FOV)]]**.
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===== Projection =====
{{  en:documentation:chart_projection.jpg|}}

For every FOV range you can choose from four projection types:
  * **ARC** Zenithal equidistant. It corresponds to the projection of a Schmidt camera.
  * **TAN** Gnomonic. This is the default projection up to 90°. Corresponds to the projection of a picture obtained with a telescope or a photographic lens. The tangent projection has a great distortion for fields larger than 90° and diverge for 180°
  * **SIN** Slant orthographic. Used to display images in radio-astronomy. The sine projection overlaps at more than 90°.
  * **CAR** Cartesian. It is of no great interest, apart from the fact that it can display very large field of views.
  * **MER** Mercator. A good projection for large fields but diverge at the pole. This is the default projection between 90° and 360°.
  * **HAI** Hammer-Aitoff. A compromise often use for large fields.

{{en:documentation:projection_mode.png|  }} \\ The three zenithal projections by E. Griessen, AIPS memo 27

By default the projection CAR, MER and HAI are oblique, i.e the projection equator is moved at the chart center. This minimize the distortion on the chart.\\ 
If you want the classic aspect of this projections you need to remove the corresponding check box. \\
See the [[projection comparison]] page for more information.


===== Object Filter =====
{{  en:documentation:chart_object_filter.jpg|}}

By this tab you can configure magnitude limits to display stars and deep sky objects based upon the FOV of your chart.

The **Stars Filter** can be:
  * disabled. (only practical with the smaller FOVs), 
  * automatic. By this you can specify a magnitude as **Naked eye reference**,
  * manual. Now you can specify a magnitude limit for every FOV range. 
A funny excercise: There's no technical problem to disable the stars filter in combination with a large **[[catalog#CDC_Stars|active star catalog]]** (i.e. HST GSC), a high value for //field number max// (i.e. 6) and a **[[menuchart#field_of_vision|FOV]]** of 20 degrees. Now you can see why a disabled Stars filter in a large FOV is not very convenient.
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{{en:documentation:chart_object_filter_manual.jpg|}}

**Deep Sky Filter** can be:
  * disabled (only practical with the smaller FOVs), 
  * manual. Here you can specify the magnitude limit for every FOV range.

You can also filter large deep sky objects specifying the maximum dimension in minutes.

===== Grid Spacing =====
{{  en:documentation:chart_grid_spacing.jpg?300|}}

By this tab you can set the grid spacing for every FOV range.
  * **Degree** is for the spacing altitude or declination direction 
  * **Hour** is for the azimuth or right ascension direction 

You can enable or disable the grid display for every FOV range.

You can enable or disable the display of a compass, you also can adjust its size or disable it.\\
You can use a simple N/E pointer instead of the compass.

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You can enable or disable the display of grids from the menu by **Chart -> Lines / Grid -> [[menuchart#Lines_-_grid|[Show coordinate grid/add equatorial grid]]]** 
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===== Object List Setting =====
{{  en:documentation:chart_objects.jpg|}}

By this tab, you determine which object types are to be filtered from your chart to your **[[Object_List|Object List]]**.
Click on the {{en:documentation:i46.png|}} icon from the **[[main_bar#Objects List|main bar]]** to retrieve your filtered list of objects displayed on the chart.
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