Merge remote-tracking branch 'origin/smooth-elevation'

17 files changed, 360 insertions, 75 deletions

diff --git a/fietsboek/actions.py b/fietsboek/actions.py
index b81b56f..29d7043 100644
--- a/fietsboek/actions.py
+++ b/fietsboek/actions.py
@@ -216,27 +216,11 @@ def execute_transformers(request: Request, track: models.Track):
         LOGGER.debug("Applied transformations match on %d, skipping", track.id)
         return
 
-    # We always start with the backup, that way we don't get "deepfried GPX"
-    # files by having the same filters run multiple times on the same input.
-    # They are not idempotent after all.
-    manager = request.data_manager.open(track.id)
-    backup_bytes = manager.decompress_backup()
-    reloaded = convert.smart_convert(backup_bytes)
-    path = reloaded.path()
-
-    for transformer in settings:
-        LOGGER.debug("Running %s with %r", transformer, transformer.parameters)
-        transformer.execute(path)
-
-    track.fast_set_path(path)
-
     LOGGER.debug("Saving new transformers on %d", track.id)
     track.transformers = serialized
 
-    LOGGER.debug("Rebuilding cache for %d", track.id)
-    request.dbsession.delete(track.cache)
-    track.cache = None
-    track.ensure_cache()
+    track.execute_transformers(request.data_manager)
+
     request.dbsession.add(track.cache)
 
 
diff --git a/fietsboek/locale/de/LC_MESSAGES/messages.mo b/fietsboek/locale/de/LC_MESSAGES/messages.mo
index 2cd5007..08a51ec 100644
--- a/fietsboek/locale/de/LC_MESSAGES/messages.mo
+++ b/fietsboek/locale/de/LC_MESSAGES/messages.mo
diff --git a/fietsboek/locale/de/LC_MESSAGES/messages.po b/fietsboek/locale/de/LC_MESSAGES/messages.po
index 552880f..2fd2aad 100644
--- a/fietsboek/locale/de/LC_MESSAGES/messages.po
+++ b/fietsboek/locale/de/LC_MESSAGES/messages.po
@@ -7,7 +7,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: PROJECT VERSION\n"
 "Report-Msgid-Bugs-To: EMAIL@ADDRESS\n"
-"POT-Creation-Date: 2026-10-01 13:36+0200\n"
+"POT-Creation-Date: 2026-10-14 19:07+0200\n"
 "PO-Revision-Date: 2022-07-02 17:35+0200\n"
 "Last-Translator: FULL NAME <EMAIL@ADDRESS>\n"
 "Language: de\n"
@@ -18,11 +18,11 @@ msgstr ""
 "Content-Transfer-Encoding: 8bit\n"
 "Generated-By: Babel 2.18.0\n"
 
-#: fietsboek/actions.py:269
+#: fietsboek/actions.py:271
 msgid "email.verify_mail.subject"
 msgstr "Fietsboek Konto Bestätigung"
 
-#: fietsboek/actions.py:272
+#: fietsboek/actions.py:274
 msgid "email.verify.text"
 msgstr ""
 "Um Dein Fietsboek-Konto zu bestätigen, nutze diesen Link: {}\n"
@@ -551,8 +551,8 @@ msgstr "Schlagwörter"
 #: fietsboek/templates/details.jinja2:111
 msgid "page.details.background_tasks_in_progress"
 msgstr ""
-"Hintergrundaufgaben für diese Strecke sind noch nicht abgeschlossen. "
-"Die angezeigten Informationen sind noch unvollständig."
+"Hintergrundaufgaben für diese Strecke sind noch nicht abgeschlossen. Die "
+"angezeigten Informationen sind noch unvollständig."
 
 #: fietsboek/templates/details.jinja2:121 fietsboek/templates/edit.jinja2:10
 #: fietsboek/templates/finish_upload.jinja2:10
@@ -733,7 +733,7 @@ msgstr "Bildbeschreibung"
 msgid "page.track.form.image_description_modal.save"
 msgstr "Übernehmen"
 
-#: fietsboek/templates/edit_form.jinja2:175
+#: fietsboek/templates/edit_form.jinja2:176
 msgid "page.track.form.transformer.enable"
 msgstr "Transformation anwenden"
 
@@ -1218,26 +1218,35 @@ msgstr "Pausen entfernen"
 msgid "transformers.remove-breaks.description"
 msgstr "Diese Transformation entfernt längere Pausen aus der Aufnahme."
 
-#: fietsboek/transformers/elevation.py:43
+#: fietsboek/transformers/elevation.py:53
 msgid "transformers.fix-null-elevation.title"
 msgstr "Nullhöhen beheben"
 
-#: fietsboek/transformers/elevation.py:47
+#: fietsboek/transformers/elevation.py:57
 msgid "transformers.fix-null-elevation.description"
 msgstr ""
 "Diese Transformation passt die Höhenangabe für Punkte an, bei denen die "
 "Höhenangabe fehlt."
 
-#: fietsboek/transformers/elevation.py:109
+#: fietsboek/transformers/elevation.py:123
 msgid "transformers.fix-elevation-jumps"
 msgstr "Höhensprünge beheben"
 
-#: fietsboek/transformers/elevation.py:113
+#: fietsboek/transformers/elevation.py:127
 msgid "transformers.fix-elevation-jumps.description"
 msgstr ""
 "Diese Transformation passt die Höhenangabe für Punkte an, bei denen die "
 "Höhe sprunghaft steigt oder fällt."
 
+#: fietsboek/transformers/elevation.py:199
+msgid "transformers.smooth-elevation"
+msgstr "Höhenprofil glätten"
+
+#: fietsboek/transformers/elevation.py:203
+msgid "transformers.smooth-elevation.description"
+msgstr ""
+"Diese Transformation glättet das Höhenprofil, um Rauschen zu verringern."
+
 #: fietsboek/views/account.py:54
 msgid "flash.invalid_name"
 msgstr "Ungültiger Name"
@@ -1338,7 +1347,7 @@ msgstr "Keine Datei ausgewählt"
 msgid "flash.upload_success"
 msgstr "Hochladen erfolgreich"
 
-#: fietsboek/views/upload.py:202
+#: fietsboek/views/upload.py:203
 msgid "flash.upload_cancelled"
 msgstr "Hochladen abgebrochen"
 
diff --git a/fietsboek/locale/en/LC_MESSAGES/messages.mo b/fietsboek/locale/en/LC_MESSAGES/messages.mo
index 19b3c28..a5dbb81 100644
--- a/fietsboek/locale/en/LC_MESSAGES/messages.mo
+++ b/fietsboek/locale/en/LC_MESSAGES/messages.mo
diff --git a/fietsboek/locale/en/LC_MESSAGES/messages.po b/fietsboek/locale/en/LC_MESSAGES/messages.po
index 1feb09a..880da4b 100644
--- a/fietsboek/locale/en/LC_MESSAGES/messages.po
+++ b/fietsboek/locale/en/LC_MESSAGES/messages.po
@@ -7,7 +7,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: PROJECT VERSION\n"
 "Report-Msgid-Bugs-To: EMAIL@ADDRESS\n"
-"POT-Creation-Date: 2026-10-01 13:36+0200\n"
+"POT-Creation-Date: 2026-10-14 19:07+0200\n"
 "PO-Revision-Date: 2023-04-03 20:42+0200\n"
 "Last-Translator: \n"
 "Language: en\n"
@@ -18,11 +18,11 @@ msgstr ""
 "Content-Transfer-Encoding: 8bit\n"
 "Generated-By: Babel 2.18.0\n"
 
-#: fietsboek/actions.py:269
+#: fietsboek/actions.py:271
 msgid "email.verify_mail.subject"
 msgstr "Fietsboek Account Verification"
 
-#: fietsboek/actions.py:272
+#: fietsboek/actions.py:274
 msgid "email.verify.text"
 msgstr ""
 "To verify your Fietsboek account, please use this link: {}\n"
@@ -549,8 +549,8 @@ msgstr "Tagged as"
 #: fietsboek/templates/details.jinja2:111
 msgid "page.details.background_tasks_in_progress"
 msgstr ""
-"Background tasks for this track are still running. "
-"The information displayed is still incomplete."
+"Background tasks for this track are still running. The information "
+"displayed is still incomplete."
 
 #: fietsboek/templates/details.jinja2:121 fietsboek/templates/edit.jinja2:10
 #: fietsboek/templates/finish_upload.jinja2:10
@@ -729,7 +729,7 @@ msgstr "Image description"
 msgid "page.track.form.image_description_modal.save"
 msgstr "Apply"
 
-#: fietsboek/templates/edit_form.jinja2:175
+#: fietsboek/templates/edit_form.jinja2:176
 msgid "page.track.form.transformer.enable"
 msgstr "Apply transformation"
 
@@ -1212,22 +1212,31 @@ msgstr "Remove breaks"
 msgid "transformers.remove-breaks.description"
 msgstr "This transformer removes long breaks from the recording"
 
-#: fietsboek/transformers/elevation.py:43
+#: fietsboek/transformers/elevation.py:53
 msgid "transformers.fix-null-elevation.title"
 msgstr "Fix null elevation"
 
-#: fietsboek/transformers/elevation.py:47
+#: fietsboek/transformers/elevation.py:57
 msgid "transformers.fix-null-elevation.description"
 msgstr "This transformer fixes the elevation of points whose elevation is unset."
 
-#: fietsboek/transformers/elevation.py:109
+#: fietsboek/transformers/elevation.py:123
 msgid "transformers.fix-elevation-jumps"
 msgstr "Fix elevation jumps"
 
-#: fietsboek/transformers/elevation.py:113
+#: fietsboek/transformers/elevation.py:127
 msgid "transformers.fix-elevation-jumps.description"
 msgstr "This transformer fixes abrupt jumps in the elevation value."
 
+#: fietsboek/transformers/elevation.py:199
+msgid "transformers.smooth-elevation"
+msgstr "Smooth elevation profile"
+
+#: fietsboek/transformers/elevation.py:203
+msgid "transformers.smooth-elevation.description"
+msgstr ""
+"This transformer applies a smoothing to the elevation profile to reduce noise."
+
 #: fietsboek/views/account.py:54
 msgid "flash.invalid_name"
 msgstr "Invalid name"
@@ -1327,7 +1336,7 @@ msgstr "No file selected"
 msgid "flash.upload_success"
 msgstr "Upload successful"
 
-#: fietsboek/views/upload.py:202
+#: fietsboek/views/upload.py:203
 msgid "flash.upload_cancelled"
 msgstr "Upload cancelled"
 
diff --git a/fietsboek/locale/fietslog.pot b/fietsboek/locale/fietslog.pot
index 4a9e203..0a066b8 100644
--- a/fietsboek/locale/fietslog.pot
+++ b/fietsboek/locale/fietslog.pot
@@ -8,7 +8,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: PROJECT VERSION\n"
 "Report-Msgid-Bugs-To: EMAIL@ADDRESS\n"
-"POT-Creation-Date: 2026-10-01 13:36+0200\n"
+"POT-Creation-Date: 2026-10-14 19:07+0200\n"
 "PO-Revision-Date: YEAR-MO-DA HO:MI+ZONE\n"
 "Last-Translator: FULL NAME <EMAIL@ADDRESS>\n"
 "Language-Team: LANGUAGE <LL@li.org>\n"
@@ -17,11 +17,11 @@ msgstr ""
 "Content-Transfer-Encoding: 8bit\n"
 "Generated-By: Babel 2.18.0\n"
 
-#: fietsboek/actions.py:269
+#: fietsboek/actions.py:271
 msgid "email.verify_mail.subject"
 msgstr ""
 
-#: fietsboek/actions.py:272
+#: fietsboek/actions.py:274
 msgid "email.verify.text"
 msgstr ""
 
@@ -719,7 +719,7 @@ msgstr ""
 msgid "page.track.form.image_description_modal.save"
 msgstr ""
 
-#: fietsboek/templates/edit_form.jinja2:175
+#: fietsboek/templates/edit_form.jinja2:176
 msgid "page.track.form.transformer.enable"
 msgstr ""
 
@@ -1196,22 +1196,30 @@ msgstr ""
 msgid "transformers.remove-breaks.description"
 msgstr ""
 
-#: fietsboek/transformers/elevation.py:43
+#: fietsboek/transformers/elevation.py:53
 msgid "transformers.fix-null-elevation.title"
 msgstr ""
 
-#: fietsboek/transformers/elevation.py:47
+#: fietsboek/transformers/elevation.py:57
 msgid "transformers.fix-null-elevation.description"
 msgstr ""
 
-#: fietsboek/transformers/elevation.py:109
+#: fietsboek/transformers/elevation.py:123
 msgid "transformers.fix-elevation-jumps"
 msgstr ""
 
-#: fietsboek/transformers/elevation.py:113
+#: fietsboek/transformers/elevation.py:127
 msgid "transformers.fix-elevation-jumps.description"
 msgstr ""
 
+#: fietsboek/transformers/elevation.py:199
+msgid "transformers.smooth-elevation"
+msgstr ""
+
+#: fietsboek/transformers/elevation.py:203
+msgid "transformers.smooth-elevation.description"
+msgstr ""
+
 #: fietsboek/views/account.py:54
 msgid "flash.invalid_name"
 msgstr ""
@@ -1308,7 +1316,7 @@ msgstr ""
 msgid "flash.upload_success"
 msgstr ""
 
-#: fietsboek/views/upload.py:202
+#: fietsboek/views/upload.py:203
 msgid "flash.upload_cancelled"
 msgstr ""
 
diff --git a/fietsboek/models/track.py b/fietsboek/models/track.py
index 361cc12..13787c8 100644
--- a/fietsboek/models/track.py
+++ b/fietsboek/models/track.py
@@ -54,6 +54,7 @@ from sqlalchemy import (
 from sqlalchemy.orm import Mapped, mapped_column, relationship
 
 from .. import geo, util
+from ..data import DataManager
 from .meta import Base
 
 if TYPE_CHECKING:
@@ -618,7 +619,7 @@ class Track(Base):
         if not self.transformers:
             return None
 
-        if not isinstance(self.transformers, dict):
+        if not isinstance(self.transformers, list):
             return None
 
         for t_id, settings in self.transformers:
@@ -626,6 +627,45 @@ class Track(Base):
                 return settings
         return None
 
+    def execute_transformers(self, data_manager: DataManager):
+        """Makes sure that the transformers applied to this track match what they should be.
+
+        The track's data is loaded fresh from the backup (as given by the data manager).
+        """
+        # The conversion returns a Track, so it imports this model.
+        # pylint: disable=import-outside-toplevel,cyclic-import
+        from .. import convert, transformers
+
+        if self.transformers is None:
+            return
+
+        manager = data_manager.open(self.id)
+        backup_bytes = manager.decompress_backup()
+        reloaded = convert.smart_convert(backup_bytes)
+        path = reloaded.path()
+
+        if not isinstance(self.transformers, list):
+            raise ValueError("Track.transformers should be a list or None")
+
+        for transformer_id, parameters in self.transformers:
+            if not isinstance(parameters, dict):
+                LOGGER.debug("Invalid parameters on track %s: %r", self.id, parameters)
+                continue
+            transformer_cls = transformers.get_transformer(transformer_id)
+            if transformer_cls is None:
+                LOGGER.info("Unknown transformer set in track %s: %s", self.id, transformer_id)
+                continue
+            transformer = transformer_cls()
+            transformer.parameters = transformer.parameter_model()(**parameters)
+            LOGGER.debug("Running %s with %r", transformer, transformer.parameters)
+            transformer.execute(path)
+
+        self.fast_set_path(path)
+
+        LOGGER.debug("Rebuilding cache for %d", self.id)
+        self.cache = None
+        self.ensure_cache()
+
 
 class TrackWithMetadata:
     """A class to add metadata to a :class:`Track`.
diff --git a/fietsboek/templates/edit.jinja2 b/fietsboek/templates/edit.jinja2
index 26c520f..a195082 100644
--- a/fietsboek/templates/edit.jinja2
+++ b/fietsboek/templates/edit.jinja2
@@ -14,7 +14,7 @@
       <label class="form-label ui-element" for="newGpx">{{ _("page.edit.form.new_track") }}</label>
       <input id="newGpx" name="gpx" type="file" class="form-control ui-element">
     </div>
-    {{ edit_form.edit_track(track.title, track.date_raw, track.date_tz or 0, track.visibility, track.type, track.description, track.text_tags(), badges, track.tagged_people, images) }}
+    {{ edit_form.edit_track(track.title, track.date_raw, track.date_tz or 0, track.visibility, track.type, track.description, track.text_tags(), badges, track.tagged_people, images, False) }}
     {{ util.hidden_csrf_input() }}
     <div class="btn-group" role="group">
         <button type="submit" class="btn btn-primary ui-element"><i class="bi bi-save"></i> {{ _("page.edit.form.submit") }}</button>
diff --git a/fietsboek/templates/edit_form.jinja2 b/fietsboek/templates/edit_form.jinja2
index e515c3b..371accc 100644
--- a/fietsboek/templates/edit_form.jinja2
+++ b/fietsboek/templates/edit_form.jinja2
@@ -1,4 +1,4 @@
-{% macro edit_track(title, date, date_tz, visibility, type, description, tags, badges, friends, images) %}
+{% macro edit_track(title, date, date_tz, visibility, type, description, tags, badges, friends, images, enable_default_transformers) %}
 <div class="mb-3">
   <label for="formTitle" class="form-label">{{ _("page.track.form.title") }}</label>
   <input class="form-control ui-element" type="text" id="formTitle" name="title" value="{{ title | default("", true) }}">
@@ -165,12 +165,13 @@
     <div id="transformer-{{ loop.index}}" class="accordion-collapse collapse" aria-labelledby="transformer-heading-{{ loop.index }}">
       <div class="accordion-body">
         {% set params = track.transformer_params_for(transformer.identifier()) if track else None %}
+        {% set enabled = params is not none or (enable_default_transformers and transformer.enabled_by_default()) %}
         <!-- Short transformer description -->
         <p>{{ _(transformer.description()) }}</p>
 
         <!-- Checkbox to enable the transformer -->
         <div class="form-check">
-          <input class="form-check-input" type="checkbox" value="on" id="transformer-enabled-{{ loop.index }}" name="transformer[{{ transformer.identifier() }}]"{% if params is not none %} checked{% endif %}>
+          <input class="form-check-input" type="checkbox" value="on" id="transformer-enabled-{{ loop.index }}" name="transformer[{{ transformer.identifier() }}]"{% if enabled %} checked{% endif %}>
           <label class="form-check-label" for="transformer-enabled-{{ loop.index }}">
             {{ _("page.track.form.transformer.enable") }}
           </label>
diff --git a/fietsboek/templates/finish_upload.jinja2 b/fietsboek/templates/finish_upload.jinja2
index 34d4aac..b8491ec 100644
--- a/fietsboek/templates/finish_upload.jinja2
+++ b/fietsboek/templates/finish_upload.jinja2
@@ -10,7 +10,7 @@
     <noscript><p>{{ _("page.noscript") }}<p></noscript>
   </div>
   <form method="POST" enctype="multipart/form-data">
-    {{ edit_form.edit_track(upload_title, upload_date, upload_date_tz, upload_visibility, upload_type, upload_description, upload_tags, badges, upload_tagged_people, []) }}
+    {{ edit_form.edit_track(upload_title, upload_date, upload_date_tz, upload_visibility, upload_type, upload_description, upload_tags, badges, upload_tagged_people, [], True) }}
     {{ util.hidden_csrf_input() }}
     <div class="btn-group" role="group">
       <button type="submit" class="btn btn-primary ui-element">{{ _("page.upload.form.submit") }}</button>
diff --git a/fietsboek/transformers/__init__.py b/fietsboek/transformers/__init__.py
index 097fbaf..4542721 100644
--- a/fietsboek/transformers/__init__.py
+++ b/fietsboek/transformers/__init__.py
@@ -95,6 +95,11 @@ class Transformer(ABC):
 
     @classmethod
     @abstractmethod
+    def enabled_by_default(cls) -> bool:
+        """Whether this transformer should be enabled by default."""
+
+    @classmethod
+    @abstractmethod
     def parameter_model(cls: type[T]) -> type[Parameters]:
         """Returns the parameter model that this transformer expects.
 
@@ -135,15 +140,28 @@ def list_transformers() -> list[type[Transformer]]:
     """
     # pylint: disable=import-outside-toplevel,cyclic-import
     from .breaks import RemoveBreaks
-    from .elevation import FixElevationJumps, FixNullElevation
+    from .elevation import FixElevationJumps, FixNullElevation, SmoothElevation
 
     return [
         FixNullElevation,
         FixElevationJumps,
         RemoveBreaks,
+        SmoothElevation,
     ]
 
 
+def get_transformer(identifier: str) -> type[Transformer] | None:
+    """Retrieve the transformer with the given identifier.
+
+    :param identifier: The identifier of the transformer to retrieve.
+    :return: The class of the transformer.
+    """
+    for transformer in list_transformers():
+        if transformer.identifier() == identifier:
+            return transformer
+    return None
+
+
 def extract_from_request(request: Request) -> list[Transformer]:
     """Extracts the list of transformers to execute from the given request.
 
diff --git a/fietsboek/transformers/breaks.py b/fietsboek/transformers/breaks.py
index 1072eef..81aca5a 100644
--- a/fietsboek/transformers/breaks.py
+++ b/fietsboek/transformers/breaks.py
@@ -36,6 +36,10 @@ class RemoveBreaks(Transformer):
         return _("transformers.remove-breaks.description")
 
     @classmethod
+    def enabled_by_default(cls) -> bool:
+        return False
+
+    @classmethod
     def parameter_model(cls) -> type[Parameters]:
         return Parameters
 
diff --git a/fietsboek/transformers/elevation.py b/fietsboek/transformers/elevation.py
index 27683bb..ad44340 100644
--- a/fietsboek/transformers/elevation.py
+++ b/fietsboek/transformers/elevation.py
@@ -1,16 +1,26 @@
 """Transformers that deal with elevation changes in the track."""
 
+import logging
+import statistics
 from collections.abc import Callable, Iterable
 from itertools import islice, zip_longest
 
 from pyramid.i18n import TranslationString
+from SGCC import savgol  # type: ignore
 
 from .. import geo
 from . import Parameters, Transformer
 
 _ = TranslationString
 
+LOGGER = logging.getLogger(__name__)
 MAX_ORGANIC_SLOPE: float = 1.0
+ELEVATION_SMOOTHING_WINDOW_LENGTH: float = 500.0
+"""One-sided window length (in m) of the elevation smoothing filter.
+
+The filtering will estimate how many points need to be included to reach this
+length.
+"""
 
 
 def slope(point_a: geo.Point, point_b: geo.Point) -> float:
@@ -47,6 +57,10 @@ class FixNullElevation(Transformer):
         return _("transformers.fix-null-elevation.description")
 
     @classmethod
+    def enabled_by_default(cls) -> bool:
+        return True
+
+    @classmethod
     def parameter_model(cls) -> type[Parameters]:
         return Parameters
 
@@ -113,6 +127,10 @@ class FixElevationJumps(Transformer):
         return _("transformers.fix-elevation-jumps.description")
 
     @classmethod
+    def enabled_by_default(cls) -> bool:
+        return False
+
+    @classmethod
     def parameter_model(cls) -> type[Parameters]:
         return Parameters
 
@@ -137,4 +155,112 @@ class FixElevationJumps(Transformer):
             current_point.elevation += point_adjustment
 
 
-__all__ = ["FixNullElevation", "FixElevationJumps"]
+class SmoothElevation(Transformer):
+    """A transformer that smooths the elevation.
+
+    **Technical description:**
+
+    This transformer has the goal of smoothing out noise in the GPS elevation
+    recording, while keeping the overall elevation profile true to the original.
+    We do this in two parts: First, we estimate the noisiness of the input data.
+    Then we apply a `Savitzky-Golay`_ filter, whose strength is scaled by the
+    noisiness estimated in the first step.
+
+    .. _Savitzky-Golay: https://en.wikipedia.org/wiki/Savitzky%E2%80%93Golay_filter
+
+    **Step 1:** Noise estimation
+
+    To estimate the noisiness, we walk through the file in windows of 5 points.
+    We do a linear regression through those points, and compute the sum of
+    absolute errors.
+
+    The reason behind this is that we assume that the profile given by 5 points
+    can be approximated reasonably with a straight line, so deviations from this
+    line are likely caused by noise in the recording.
+
+    We average the sum-of-errors over all windows in the track to reach the
+    track's total noisiness, this prevents outlier windows from affecting the
+    noisiness too much.
+
+    **Step 2:** Filter
+
+    The actual smoothing is done with a pass of the Savitzky-Golay filter. The
+    window size :math:`w` is scaled linearly according to the noisiness
+    :math:`w` determined in step 1 as :math:`w = n \\cdot f`. The factor
+    :math:`f` is fixed and determined manually with some example tracks.
+    """
+
+    @classmethod
+    def identifier(cls) -> str:
+        return "smooth-elevation"
+
+    @classmethod
+    def name(cls) -> TranslationString:
+        return _("transformers.smooth-elevation")
+
+    @classmethod
+    def description(cls) -> TranslationString:
+        return _("transformers.smooth-elevation.description")
+
+    @classmethod
+    def enabled_by_default(cls) -> bool:
+        return True
+
+    @classmethod
+    def parameter_model(cls) -> type[Parameters]:
+        return Parameters
+
+    @property
+    def parameters(self) -> Parameters:
+        return Parameters()
+
+    @parameters.setter
+    def parameters(self, value):
+        pass
+
+    def execute(self, path: geo.Path):
+        radius = self._estimate_window_size(path)
+        radius = min(radius, int(len(path.points) / 2))
+        LOGGER.debug("Savitzky-Golay radius: %s", radius)
+        if radius:
+            self._savitzky_golay(path, radius)
+
+    def _snr(self, path: geo.Path) -> float:
+        window_size = 5
+        errors: list[float] = []
+        for start in range(0, len(path.points) - window_size):
+            elevations = [point.elevation for point in path.points[start : start + window_size]]
+            xs = list(range(len(elevations)))
+
+            sl, intercept = statistics.linear_regression(xs, elevations)
+            errors.extend(
+                abs(elevation - (x * sl + intercept)) for x, elevation in enumerate(elevations)
+            )
+        return statistics.mean(errors)
+
+    def _estimate_window_size(self, path: geo.Path) -> int:
+        points_per_meter = len(path.points) / path.movement_data().length
+        snr = self._snr(path)
+        window_length = 6 * ELEVATION_SMOOTHING_WINDOW_LENGTH * snr
+        LOGGER.debug("signal-to-noise=%s, points_per_meter=%s", snr, points_per_meter)
+        return int(points_per_meter * window_length)
+
+    def _savitzky_golay(self, path: geo.Path, radius: int):
+        elevations = [0.0] * len(path.points)
+        coeffs = savgol.get_coefficients(0, 2, 2 * radius + 1, 0)
+
+        for i in range(0, radius + 1):
+            elevations[i] = path.points[i].elevation
+            elevations[-i - 1] = path.points[-i - 1].elevation
+
+        for i in range(radius, len(path.points) - radius - 1):
+            points = path.points[i - radius : i + radius + 1]
+            assert len(points) == len(coeffs)
+            smoothed = sum(coef * point.elevation for coef, point in zip(coeffs, points))
+            elevations[i] = smoothed
+
+        for i, elevation in enumerate(elevations):
+            path.points[i].elevation = elevation
+
+
+__all__ = ["FixNullElevation", "FixElevationJumps", "SmoothElevation"]
diff --git a/fietsboek/updater/scripts/upd_20261015_gg7gfmpk4nxl062z.py b/fietsboek/updater/scripts/upd_20261015_gg7gfmpk4nxl062z.py
new file mode 100644
index 0000000..4168c5d
--- /dev/null
+++ b/fietsboek/updater/scripts/upd_20261015_gg7gfmpk4nxl062z.py
@@ -0,0 +1,69 @@
+"""Revision upgrade script gg7gfmpk4nxl062z
+
+Active the "smooth elevation" transformer.
+
+Date created: 2026-10-15 14:22:06.047695
+"""
+from pathlib import Path
+
+from sqlalchemy import select
+from sqlalchemy.orm import Session
+from sqlalchemy.orm.attributes import flag_modified
+
+from fietsboek import models
+from fietsboek.data import DataManager
+from fietsboek.updater.script import UpdateScript
+
+update_id = 'gg7gfmpk4nxl062z'
+previous = [
+    '7fa8kflikvnlvuqe',
+]
+alembic_revision = 'b73ed8b45f67'
+
+
+class Up(UpdateScript):
+    def pre_alembic(self, config):
+        pass
+
+    def post_alembic(self, config):
+        data_manager = DataManager(Path(config["fietsboek.data_dir"]))
+        engine = self.dbengine(config)
+        session = Session(engine)
+
+        with Session(engine) as session:
+            query = select(models.Track)
+            for track in session.execute(query).scalars():
+                if track.type != models.track.TrackType.ORGANIC:
+                    continue
+                self.tell(f"Applying smoothing to track {track.id}")
+                track.transformers.append(["smooth-elevation", {}])
+                flag_modified(track, "transformers")
+                track.execute_transformers(data_manager)
+                session.add(track)
+                session.add(track.cache)
+            session.commit()
+
+
+class Down(UpdateScript):
+    def pre_alembic(self, config):
+        pass
+
+    def post_alembic(self, config):
+        data_manager = DataManager(Path(config["fietsboek.data_dir"]))
+        engine = self.dbengine(config)
+        session = Session(engine)
+
+        with Session(engine) as session:
+            query = select(models.Track)
+            for track in session.execute(query).scalars():
+                if track.type != models.track.TrackType.ORGANIC:
+                    continue
+                self.tell(f"Removing smoothing from track {track.id}")
+                unsmoothed = [[k, v] for k, v in track.transformers if k != "smooth-elevation"]
+                if unsmoothed == track.transformers:
+                    continue
+                track.transformers = unsmoothed
+                track.execute_transformers(data_manager)
+                session.add(track)
+                session.add(track.cache)
+            session.commit()
diff --git a/poetry.lock b/poetry.lock
index 3fc3a7a..251bc18 100644
--- a/poetry.lock
+++ b/poetry.lock
@@ -1,4 +1,4 @@
-# This file is automatically @generated by Poetry 2.3.3 and should not be changed by hand.
+# This file is automatically @generated by Poetry 2.3.1 and should not be changed by hand.
 
 [[package]]
 name = "alabaster"
@@ -2706,6 +2706,18 @@ files = [
 ]
 
 [[package]]
+name = "savgol-calculator"
+version = "1.0.5"
+description = "Python implementation of a coefficients calculator for the Savitsky-Golay filter with any parameters."
+optional = false
+python-versions = ">=3.6.0"
+groups = ["main"]
+files = [
+    {file = "savgol-calculator-1.0.5.tar.gz", hash = "sha256:f0e49fdc1944f1aab3fda644d0b1d2fa9f6cd8f2e204599c0cf00c59234fbed3"},
+    {file = "savgol_calculator-1.0.5-py2.py3-none-any.whl", hash = "sha256:dd0db764ea9322b593f04e8bafbed383a205ae125ef4330f795e30aceaa69c7e"},
+]
+
+[[package]]
 name = "setuptools"
 version = "82.0.1"
 description = "Most extensible Python build backend with support for C/C++ extension modules"
@@ -3489,4 +3501,4 @@ test = ["zope.testing"]
 [metadata]
 lock-version = "2.1"
 python-versions = ">=3.11, <4"
-content-hash = "b4d90215cb83febb48f381f7eb9d8d2aa4fe159a34bfb93b96fbef54ea943881"
+content-hash = "1fd62aecf611f739cc79de3ea6a6f69665ca822960e9bde75954c8d255764ac3"
diff --git a/pyproject.toml b/pyproject.toml
index d3d22a1..e4c4347 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -46,6 +46,7 @@ dependencies = [
     "matplotlib (>=3.10.7,<4.0.0)",
 
     "hittekaart-py @ git+https://gitlab.com/dunj3/hittekaart@9a576a8d3a8cb1d143be0ade0310f71b490cacb9#subdirectory=hittekaart-py",
+    "savgol-calculator (==1.0.5)",
 ]
 
 [project.urls]
diff --git a/tests/playwright/test_transformers.py b/tests/playwright/test_transformers.py
index d4e3456..cc897db 100644
--- a/tests/playwright/test_transformers.py
+++ b/tests/playwright/test_transformers.py
@@ -13,6 +13,17 @@ def disable_cache(page: Page):
     page.route("**", lambda route: route.continue_())
 
 
+def set_transformers(page: Page, states: list[bool]):
+    """Enable/disable the transformers according to the given states."""
+    for i, state in enumerate(states, start=1):
+        page.locator(f"#transformer-heading-{i} .accordion-button").click()
+        page.locator(f"#transformer-{i}.collapse.show").wait_for()
+        if state:
+            page.locator(f"#transformer-enabled-{i}").check()
+        else:
+            page.locator(f"#transformer-enabled-{i}").uncheck()
+
+
 def test_transformer_zero_elevation_disabled(page: Page, playwright_helper, tmp_path, dbaccess):
     playwright_helper.login()
 
@@ -21,6 +32,8 @@ def test_transformer_zero_elevation_disabled(page: Page, playwright_helper, tmp_
 
     extract_and_upload(page, "Synthetic_Zero_Elevation.gpx.gz", tmp_path)
 
+    set_transformers(page, [False, False, False, False])
+
     page.locator(".btn", has_text="Upload").click()
 
     # Expect early (here and in the other tests) to ensure that the backend has
@@ -41,9 +54,7 @@ def test_transformer_zero_elevation_enabled(page: Page, playwright_helper, tmp_p
 
     extract_and_upload(page, "Synthetic_Zero_Elevation.gpx.gz", tmp_path)
 
-    page.locator("#transformer-heading-1 .accordion-button").click()
-    page.locator("#transformer-1.collapse.show").wait_for()
-    page.locator("#transformer-enabled-1").check()
+    set_transformers(page, [True, False, False, False])
 
     page.locator(".btn", has_text="Upload").click()
 
@@ -62,14 +73,13 @@ def test_transformer_zero_elevation_edited(page: Page, playwright_helper, tmp_pa
     page.get_by_text("Upload").click()
 
     extract_and_upload(page, "Synthetic_Zero_Elevation.gpx.gz", tmp_path)
+    set_transformers(page, [False, False, False, False])
 
     page.locator(".btn", has_text="Upload").click()
 
     page.locator(".btn", has_text="Edit").click()
 
-    page.locator("#transformer-heading-1 .accordion-button").click()
-    page.locator("#transformer-1.collapse.show").wait_for()
-    page.locator("#transformer-enabled-1").check()
+    set_transformers(page, [True, False, False, False])
 
     page.locator(".btn", has_text="Save").click()
 
@@ -87,6 +97,7 @@ def test_transformer_steep_slope_disabled(page: Page, playwright_helper, tmp_pat
     page.get_by_text("Upload").click()
 
     extract_and_upload(page, "Synthetic_Steep_Slope.gpx.gz", tmp_path)
+    set_transformers(page, [False, False, False, False])
 
     page.locator(".btn", has_text="Upload").click()
 
@@ -104,10 +115,7 @@ def test_transformer_steep_slope_enabled(page: Page, playwright_helper, tmp_path
     page.get_by_text("Upload").click()
 
     extract_and_upload(page, "Synthetic_Steep_Slope.gpx.gz", tmp_path)
-
-    page.locator("#transformer-heading-1 .accordion-button").click()
-    page.locator("#transformer-1.collapse.show").wait_for()
-    page.locator("#transformer-enabled-1").check()
+    set_transformers(page, [True, False, False, False])
 
     page.locator(".btn", has_text="Upload").click()
 
@@ -126,14 +134,13 @@ def test_transformer_steep_slope_edited(page: Page, playwright_helper, tmp_path,
     page.get_by_text("Upload").click()
 
     extract_and_upload(page, "Synthetic_Steep_Slope.gpx.gz", tmp_path)
+    set_transformers(page, [False, False, False, False])
 
     page.locator(".btn", has_text="Upload").click()
 
     page.locator(".btn", has_text="Edit").click()
 
-    page.locator("#transformer-heading-1 .accordion-button").click()
-    page.locator("#transformer-1.collapse.show").wait_for()
-    page.locator("#transformer-enabled-1").check()
+    set_transformers(page, [True, False, False, False])
 
     page.locator(".btn", has_text="Save").click()
 
@@ -151,10 +158,7 @@ def test_transformer_elevation_jump_enabled(page: Page, playwright_helper, tmp_p
     page.get_by_text("Upload").click()
 
     extract_and_upload(page, "Elevation_Jump.gpx.gz", tmp_path)
-
-    page.locator("#transformer-heading-2 .accordion-button").click()
-    page.locator("#transformer-2.collapse.show").wait_for()
-    page.locator("#transformer-enabled-2").check()
+    set_transformers(page, [False, True, False, False])
 
     page.locator(".btn", has_text="Upload").click()