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--- en:documentation:chart_coordinates [2012/08/09 10:14] – modification externe 127.0.0.1
+++ en:documentation:chart_coordinates [2016/08/14 19:16] (current) – [Type of coordinates] pch
@@ Line 14: / Line 14: @@
 ==== Chart Setting ====
 {{  en:documentation:chart_coordinates.jpg|}}
 Here, you can specify the coordinate system used for the chart.
 The four available systems are:
@@ Line 25: / Line 26: @@
 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, ...**
+  * **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 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 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 ...**
+  * **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.
 \\ \\
 {{  en:documentation:chart_coordinates_expert.jpg|}}
 In **Expert mode** you can specify more details :
   * **Equinox** year (from -20000 to 20000)
@@ Line 44: / Line 46: @@
 ===== Field of Vision =====
 {{  en:documentation:chart_fov.jpg|}}
 Here you can specify eleven ranges as the Field of Vision (numbered from 0 to 10).
@@ Line 52: / Line 55: @@
 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.
 \\ \\
-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_and_field_of_vision#field_of_vision_fov|Field of Vision (FOV)]]**.
+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)]]**.
 \\ \\ \\
+\\ \\ \\
 ===== Projection =====
 {{  en:documentation:chart_projection.jpg|}}
 For every FOV range you can choose from four projection types:
-  * **ARC** Arc length. This is the default projection up to 180°. It corresponds to the projection of a Schmidt camera.
+  * **ARC** Zenithal equidistant. It corresponds to the projection of a Schmidt camera.
-  * **TAN** Tangent. 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 45° and diverge for 90°
+  * **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** Sine. Used to display images in radio-astronomy. The sine projection overlaps at more than 90°.
+  * **SIN** Slant orthographic. Used to display images in radio-astronomy. The sine projection overlaps at more than 90°.
-  * **CAR** Cartesian. The projection between 180° and 360°. It is of no great interest, apart from the fact that it can display very large field of views.
+  * **CAR** Cartesian. It is of no great interest, apart from the fact that it can display very large field of views.
-{{en:documentation:projection_mode.png|  }} by E. Griessen, AIPS memo 27
+  * **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.
@@ Line 75: / Line 89: @@
 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.
 \\ \\
-{{en:documentation:chart_object_filter_manual.jpg|}}\\
+{{en:documentation:chart_object_filter_manual.jpg|}}
 **Deep Sky Filter** can be:
   * disabled (only practical with the smaller FOVs),
@@ Line 83: / Line 98: @@
 ===== Grid Spacing =====
-{{  en:documentation:chart_grid_spacing.jpg|}}
+{{  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
@@ Line 90: / Line 106: @@
 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 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.
 \\ \\ \\
 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]]]**
@@ Line 97: / Line 115: @@
 ===== 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.
-\\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\
+\\ \\ \\ \\ \\ \\