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--- manual:user_guide:tools:altitude [2015/09/10 09:25] – mstupka
+++ manual:user_guide:tools:altitude [2016/10/21 16:39] – mstupka
@@ Line 10: / Line 10: @@
   * **settings of pressure sensor**
 ===== Settings =====
-{{ :manual:user_guide:tools:altmanager.png?nolink|}}
+Contains general switches of offset and pressure sensor and settings of SRTM data assistance and altitude measurement filter:\\ {{ :manual:user_guide:tools:altmanager.png }}
-==== Altitude offset ====
+====  SRTM data ====
+{{ :manual:user_guide:tools:altmanager4.png?nolink |}}
-  * **Use altitude offset** - switches on the definition of offset between real and GPS altitude. More in the **Offset tab**.
+  * **No usage** - altitude values are acquired from GPS only
-==== Pressure sensor ====
+  * **Optimize GPS altitude** - uses [[http://en.wikipedia.org/wiki/Shuttle_Radar_Topography_Mission|offline elevation data (SRTM)]] to optimize GPS altitude values. Computed altitude has similar accuracy to an average GPS but does not contain serious errors GPS units usually make. SRTM data can be downloaded [[manual:faq:how_to_add_map_shading|several ways]].
+  * **Replace GPS values** - uses [[http://en.wikipedia.org/wiki/Shuttle_Radar_Topography_Mission|offline elevation data (SRTM)]] only for displaying elevation
-  * **Use pressure sensor** - switches on measuring precise altitude by the device built-in barometric pressure sensor. More in the **Pressure tab**.
-====  Elevation data ====
-  * **Optimize GPS altitude** - uses [[http://en.wikipedia.org/wiki/Shuttle_Radar_Topography_Mission|offline elevation data (HGT)]] to optimize GPS altitude values. Computed altitude has similar accuracy to an average GPS but does not contain serious errors GPS units usually make. HGT files are downloaded usually together with LoMaps or can be additionally downloaded by a "fill altitude" command [[manual:user_guide:tracks:management#track_detail_screen|editing tracks]].
 <WRAP round alert >
-**Warning for pilots**: this method is not recommended for activities when you are **not moving on the ground** - displayed altitude values are influenced by the ground altitude measuring and calculation
+**Warning for pilots**: optimizing or replacing GPS altitude by SRTM data is not recommended for activities when you are **not moving on the ground** - displayed altitude values are influenced by the ground altitude measuring and calculation
 </WRAP>
 ==== Altitude filter ====
-  * **Filter** - applies filter to altitude to reduce value fuzziness. Heavier filters cause less fuzzy altitude values but slower reaction on altitude changes. Scale ranges from no filtration to an ultra heavy filter.
+Applies filter to altitude measurement to reduce value fuzziness. Heavier filters cause less fuzzy altitude values but slower reaction on altitude changes. Scale ranges from no filtration to an ultra heavy filter.
+===== Altitude offset =====
-===== Offset =====
+{{ :manual:user_guide:tools:altmanager2.png }}
+Altitude calculated by internal or external (Bluetooth) GPS unit is related to a different method of referencing the Earth surface than that used in maps. The difference between them is called **Geoid height** which is distance between [[http://en.wikipedia.org/wiki/Geoid|Geoid]] and [[http://en.wikipedia.org/wiki/Reference_ellipsoid|reference elipsoid]].
-{{ :manual:user_guide:tools:altmanager2.png?nolink|}}Altitude calculated by internal GPS unit is related to a different method of referencing the Earth surface than that used in maps. The difference between them is called **Geoid height** which is distance between [[http://en.wikipedia.org/wiki/Geoid|Geoid]] and [[http://en.wikipedia.org/wiki/Reference_ellipsoid|reference elipsoid]].
 Locus Map can define this offset by three methods:
@@ Line 36: / Line 30: @@
   * **Automatic correction** - method used in most cases - Locus Map can compute offset of the whole world from a Geoid model. This method is accurate enough for use in mobile phones and sufficiently precise for all locations (the offset slightly varies based on location). <wrap info>This method is available in Locus Map Pro only</wrap>
   * **Altitude NMEA correction** - mobile device communicates with GPS unit over a special messages called NMEA. These messages contain values of Geoid height that Locus Map can read and apply them to correct this offset.<wrap alert>Some devices report incorrect values so this method is unreliable.</wrap>
-===== Pressure Sensor =====
+  * **Enable also for Bluetooth GPS** - check this option if you use external GPS device
-{{ :manual:user_guide:tools:altmanager3.png?nolink|}}Some devices are equipped with barometric pressure sensor. Barometric sensors measure atmospheric pressure very precisely which can be used for calculating relative altitude changes. I.e. if you know certain pressure at certain altitude you can calculate altitude changes between known and current position.
+===== Pressure sensor =====
+{{ :manual:user_guide:tools:altmanager3.png }}
+Some devices are equipped with barometric pressure sensor. Barometric sensors measure atmospheric pressure very precisely which can be used for calculating relative altitude changes. I.e. if you know certain pressure at certain altitude you can calculate altitude changes between known and current position.
 The pressure sensor must be calibrated to a known altitude value so that it can be used for real altitude value calculations. Locus Map offers several methods:
@@ Line 44: / Line 41: @@
   * **Altitude** - uses some other source of ground altitude - external maps, measuring, tourist guide posts, etc. as the reference. Locus Map then calibrates the pressure sensor according to this value.
 <WRAP  round important>Some devices like e.g. Samsung Galaxy Note II turn off the pressure sensor in standby mode. If you want to use pressure sensor during e.g. track recording, make sure your device maintains the pressure sensor on also when the screen goes off.
 </WRAP>

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