Copter: Update terrain generator details

common/source/docs/common-terrain-following.rst

@@ -116,7 +116,7 @@ You can also download .zip files for entire continents, or individual tiles from
 
 .. warning:: A long standing bug in the downloaded terrain data files, which occasionally caused terrain data to be missing, even though supposedly downloaded, was fixed in Plane 4.0.6, Copter 4.0.4, and Rover 4.1. It will automatically be re-downloaded when connected to a compatible GCS. However, if you are relying on SD terrain data for an area and don't plan on being connected to a GCS when flying over it, or it's not part of a mission, you should download the area data using the utility above, or linked tiles data repository and place on your SD card in the Terrain directory.
 
-.. warning:: ArduPilot 4.0.x and 4.1.x use different terrain tilesets. When upgrading from 4.0.x to 4.1.x, any tiles on the SD card will need to be re-downloaded. This will happen automatically when your GCS is connected to the Internet. Otherwise, you may set the :ref:`TERRAIN_MARGIN <TERRAIN_MARGIN>` to 50 to continue using the old tileset.
+.. warning:: ArduPilot 4.0.x and 4.1.x use different terrain tilesets. When upgrading from 4.0.x to 4.1.x, any tiles on the SD card will need to be re-downloaded. This will happen automatically when your GCS is connected to the Internet for areas covered by loaded missions and/or home location. Otherwise, you may set the :ref:`TERRAIN_MARGIN <TERRAIN_MARGIN>` to 50 to continue using the old tileset.
 
 Terrain Spacing
 ===============

copter/source/docs/terrain-following.rst

@@ -47,10 +47,12 @@ Alternatively, you can download a set of terrain data tiles for any anticipated
 
 It will create tiles for the specified radius around a geographic location. Then you can download them, unzip and write in the APM/TERRAIN folder of the SD card.
 
-You can also download .zip files for entire continents, or individual tiles from `here <https://terrain.ardupilot.org/data/>`__.
+You can also download .zip files for entire continents, or individual tiles from `here <https://terrain.ardupilot.org/data/>`__. Note that ArduPilot 4.0.x and 4.1.x have different tilesets. Use the "continents"/"tiles" folders for ArduPilot 4.0.x, or use the "continentsapm41"/"tilesapm41" folders for ArduPilot 4.1.x. 
 
 .. warning:: A long standing bug in the downloaded terrain data files, which occasionally caused terrain data to be missing, even though supposedly downloaded, was fixed in Plane 4.0.6, Copter 4.0.4, and Rover 4.1. It will automatically be re-downloaded when connected to a compatible GCS. However, if you are relying on SD terrain data for an area and don't plan on being connected to a GCS when flying over it, or its not part of a mission, you should download the area data using the utility above, or from the linked tiles data repository and place on your SD card in the Terrain directory.
 
+.. warning:: ArduPilot 4.0.x and 4.1.x use different terrain tilesets. When upgrading from 4.0.x to 4.1.x, any tiles on the SD card will need to be re-downloaded. This will happen automatically when your GCS is connected to the Internet for areas covered by loaded missions and/or home location. Otherwise, you may set the :ref:`TERRAIN_MARGIN <TERRAIN_MARGIN>` to 50 to continue using the old tileset.
+
 Using Terrain Altitude during RTL and Land
 ==========================================
 Set the :ref:`TERRAIN_FOLLOW <TERRAIN_FOLLOW>` parameter to 1 to enable using terrain data in :ref:`RTL <rtl-mode>` and :ref:`Land <land-mode>` flight modes.  If set the vehicle will interpret the :ref:`RTL_ALT <RTL_ALT>` as an altitude-above-terrain meaning it will generally climb over hills on it's return path to home.  Similarly Land will slow to the :ref:`LAND_SPEED <LAND_SPEED>` (normally 50cm/s) when it is 10m above the terrain (instead of 10m above home).