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--- en:documentation:observatory [2013/11/12 08:20] – external edit 127.0.0.1
+++ en:documentation:observatory [2025/08/20 15:19] (current) – [Use an horizon picture] dokuadmin
@@ Line 41: / Line 41: @@
 It is important to select the correct time zone for your observatory because SkyCharts needs it to calculate the //UT// from your //Daylight Savings// setting. This is very important to do proper ephemeris calculations in order to display the right chart.\\
 It is recommended to use the country time zone as it correct for DST for any epoch where the rules are know.\\
-If you use the special GMT time zone, beware the hour offset sign is opposite of what you expect, zones west of GMT have a positive sign. See http://en.wikipedia.org/wiki/Tz_database#Area
+You can also use an UTC time zone if you want a fixed time along the year.
 If you frequently use this observation site you can add it to your favorites list with the Add button after all settings are right for you.
@@ Line 68: / Line 68: @@
 ===== Horizon =====
-{{  en:documentation:observatory_horizon.jpg|}}
+{{  en:documentation:observatory_horizon.jpg?330|}}
 When your chart is set to use the Alt-Az coordinate system, you can display your local horizon as a line or as an area. To read more about changing the coordinate system, click **[[menuchart#chart_coordinate_system|here]]**. \\
 You can load a local horizon file by setting the path.
@@ Line 78: / Line 79: @@
 As you can see from the file, the horizon is defined by a serie of records. Every line contains a pair of two values. The first value is the 'azimuth', the second is the 'altitude'. The units are degrees, where azimuth 0° is North and 90° is the Zenith. A dot (.) can be used as a decimal separator. You can put comment in your horizon file by lines that start with a mesh (#) character.
+==== Use an horizon picture ====
+You can also use a picture for the horizon panorama. The image must be a PNG or BMP file of any size representing the full 360° panorama with an equirectangular projection.\\
+The sky area must be set transparent for files in PNG format or set the color to magenta (#FF00FF) for the BMP format.\\
+The horizon must be exactly at the middle height of the picture, but you can cut the unused part. For example if the highest point of your horizon is at an altitude of 20°, it is sufficient to have the picture to cover from -20° to +20°. Above +20° the sky will be fully transparent and below -20° the map is filled with the configured horizon color.\\
+The left side of the picture is the East direction. If you use another orientation you must also give the offset angle. This angle can be read from the value of "angle_rotatez=" in a landscape.ini file found in the same folder as the picture.\\
+If "High quality" is checked a point is computed for every screen pixel of the map. Otherwise it compute a point only every four pixel. See the discussion about the performance below.
-==== The other possibilities ====
+This function is compatible with the horizon made for [[http://www.stellarium.org|Stellarium]] using the [[https://stellarium.org/guide/#pf65|Single Panorama Method]].\\
+So the quickest way to test it is to get a [[https://stellarium.org/en/landscapes.html|landscape file]] for Stellarium. Just be sure the format is compatible by looking at the row "type = spherical" in the landscape.ini file.\\
+For example download the [[https://www.ap-i.net/pub/skychart/horizon/landscape_jungfraujoch.zip|Jungfraujoch panorama]], unzip the file in your home folder.\\
+Launch Skychart and open the observatory setting, add an observatory location for Jungfraujoch as show here (location is not automatically set from landscape.ini but you can look at the file to get the right value):\\
+{{:en:documentation:jungfraujoch_1.jpg?300|}}
+In the horizon tab, check "Display the horizon picture", click the folder button and open the file jungfraujoch-4096.png.
+{{:en:documentation:jungfraujoch_2.jpg?300|}}
+Return to the Observatory tab and click the "Add" button to add to the favorite list with all the picture options.
+Click OK, you must see the following map:
+{{:en:documentation:jungfraujoch_3.jpg?600|}}
+**About the performance**\\
+On some situation the chart refresh performance can be very bad. The reason is because Skychart use only the main processor to display the chart, so if you have a big screen and a slow processor you can run into a problem.\\
+Using a mid-range computer with a Core I5-2500 processor and a 1600x1200 screen with the chart set to full-screen, it take 0.3 second draw the Jungfraujoch panorama.\\
+If you not get this value you can try the following:
+  * Uncheck "High quality" so the processor as four time less work to do. The quality must be enough if you use a high dpi screen (laptop with high resolution).
+  * Reduce the size of the chart window. With the same processor it take only 0.1 second for a 1024x768 window.
+  * Be sure you check "Reduce details when moving the chart" in Setup / Display.
+  * Try to cut the unused part of the picture. The Jungfraujoch panorama can be cut to 4096x1048 without loss.
+  * If you use a large picture (more than 4096 pixels) it can take a long time to load when you start Skychart. In this case try to use the BMP format that use less resources.
+**To make your own panorama**\\
+Put a camera on a tripod at the exact location you will put your telescope mount later. If you use a fixed pier, fix a photographic head on the pier. Be sure to level the tripod carefully. Try to have the camera objective near to the head rotation axis to avoid parallax problem on nearby objects.\\
+Select a moment you get the most uniform lighting in every direction. A uniform high cloud cover can be good.\\
+Get a sequence of picture for the whole horizon, be sure to have enough overlap between the pictures.\\
+Use a panorama software like [[http://hugin.sourceforge.net/|Hugin]] to assemble the pictures. Convert the result to PNG format to support transparency. Then use [[http://www.gimp.org/|GIMP]] to set the sky transparent using one of the [[https://www.google.com/search?q=gimp+mask+transparency|numerous method]] available, I found that creating a sky mask first work fine.\\
+Finally reduce the panorama size to a reasonable value, 4096 or 8192 pixel width.
+For mountainous area it possible to use an [[panorama| online panorama generator]].\\
+The condition is the horizon is limited by remote mountain, this not work for tree or nearby buildings.
+{{:en:documentation:horizon4.png?600|}}
+===== The other possibilities =====
 The other possibilities will be obvious from their description. \\
 * Maybe you want to display objects below the horizon line. \\
-* If your site is high on the moutain, maybe you want to simulate the horizon as a depressed line. \\
+* If your site is high on the mountain, maybe you want to simulate the horizon as a depressed line. \\
-Above all, you can specify temperature and air pressure. This allows SkyChart to calculate and compensate for atmospheric refraction.
+Above all, you can specify temperature, air pressure and humidity. This allows SkyChart to calculate and compensate for atmospheric refraction.
+The last line is about some small correction for the Earth pole orientation. You can find the required prediction data in the latest [[http://www.iers.org/IERS/EN/Publications/Bulletins/bulletins.html|IERS Bulletins A]] :
+<code>
+                     MJD      x(arcsec)   y(arcsec)   UT1-UTC(sec)
+  1 31  56688       0.0245      0.3483     -0.12827
+</code>
+For example for 2014 January 31 use X=0.0245 and Y=0.3483