add docs for fix elevation jump transformer

3 files changed, 29 insertions, 0 deletions

diff --git a/doc/user/images/fixed_elevation_jump.png b/doc/user/images/fixed_elevation_jump.png
new file mode 100644
index 0000000..4d1334a
--- /dev/null
+++ b/doc/user/images/fixed_elevation_jump.png
diff --git a/doc/user/images/wrong_elevation_jump.png b/doc/user/images/wrong_elevation_jump.png
new file mode 100644
index 0000000..03d454d
--- /dev/null
+++ b/doc/user/images/wrong_elevation_jump.png
diff --git a/doc/user/transformers.rst b/doc/user/transformers.rst
index d053052..7ce4bc7 100644
--- a/doc/user/transformers.rst
+++ b/doc/user/transformers.rst
@@ -19,6 +19,11 @@ In other applications, transformers are sometimes called "filters". That term
 however has many different meanings (like the filters on the "Browse" page),
 and as such, Fietsboek calls them transformers.
 
+Keep in mind that the transformers provide a "quick and convenient" way to
+apply a predefined set of changes to a track. If you need to do fine-grained
+edits to a GPX file, you need to use a different tool and edit the file before
+uploading it to Fietsboek.
+
 Fix Null Elevation
 ------------------
 
@@ -44,6 +49,30 @@ point.
 To fix those points, the transformer will find the first correct point, and
 copy its elevation to the wrong points.
 
+Fix Elevation Jumps
+-------------------
+
+The *fix elevation jumps* transformer eliminates big elevation jumps in the
+middle of a track. This is useful to deal with "stitched" GPX files, where the
+elevation is consistent within a single track, but the absolute value might not
+be correct (e.g. if the device recalibrates):
+
+.. image:: images/wrong_elevation_jump.png
+   :width: 600
+   :alt: The elevation profile having a big jump in the middle.
+
+In this track, the device was re-calibrated mid-track. The transformer will
+adjust the elevation values:
+
+.. image:: images/fixed_elevation_jump.png
+   :width: 600
+   :alt: The same elevation profile with the jump removed.
+
+The detection of jumps work similarly to the *fix null elevation* transformer,
+with the difference that it works in the middle of tracks. It will consider the
+earlier points as anchor, and then adjust the later points such that the first
+point after the jump has the same elevation as the last point before the jump.
+
 Remove Breaks
 -------------