diff --git a/src/ifcviewer-full/MainWindow.cpp b/src/ifcviewer-full/MainWindow.cpp
index 0fd00530b1..8dda5cfd42 100644
--- a/src/ifcviewer-full/MainWindow.cpp
+++ b/src/ifcviewer-full/MainWindow.cpp
@@ -21,6 +21,7 @@
 #include "AppSettings.h"
 #include "Federation.h"
 #include "FederationSettingsDialog.h"
+#include "ModelTransformationDialog.h"
 #include "SettingsWindow.h"
 #include "LodBuilder.h"
 #include "SidecarCache.h"
@@ -192,6 +193,8 @@ void MainWindow::setupMenus() {
                          QKeySequence::SaveAs);
     file_menu->addAction("Federation Se&ttings...",
                          this, &MainWindow::onFederationSettings);
+    file_menu->addAction("&Model Transformations...",
+                         this, &MainWindow::onModelTransformations);
     file_menu->addSeparator();
     file_menu->addAction("&Settings...", this, &MainWindow::onFileSettings);
     file_menu->addSeparator();
@@ -240,6 +243,15 @@ void MainWindow::onFederationSettings() {
     federation_settings_->raise();
 }
 
+void MainWindow::onModelTransformations() {
+    if (model_transformations_ == nullptr) {
+        model_transformations_ = new ModelTransformationDialog(federation_, this);
+    }
+    model_transformations_->open();
+    model_transformations_->activateWindow();
+    model_transformations_->raise();
+}
+
 void MainWindow::addFiles(const QStringList& paths) {
     QStringList accepted_paths;
     QStringList accepted_fed_ids;
diff --git a/src/ifcviewer-full/MainWindow.h b/src/ifcviewer-full/MainWindow.h
index 20a514c073..85bd6b2473 100644
--- a/src/ifcviewer-full/MainWindow.h
+++ b/src/ifcviewer-full/MainWindow.h
@@ -37,6 +37,7 @@
 class Federation;
 class SettingsWindow;
 class FederationSettingsDialog;
+class ModelTransformationDialog;
 
 class MainWindow : public QMainWindow {
     Q_OBJECT
@@ -63,6 +64,7 @@ private slots:
     void onGoHomeView();
     void onFileSettings();
     void onFederationSettings();
+    void onModelTransformations();
     void onObjectPicked(uint32_t object_id);
     void onTreeSelectionChanged();
 
@@ -122,6 +124,7 @@ private:
     Federation*     federation_ = nullptr;
     SettingsWindow* settings_ = nullptr;
     FederationSettingsDialog* federation_settings_ = nullptr;
+    ModelTransformationDialog* model_transformations_ = nullptr;
     QWidget* viewport_container_ = nullptr;
     QTreeWidget* element_tree_ = nullptr;
     QTableWidget* property_table_ = nullptr;
diff --git a/src/ifcviewer-full/ModelTransformationDialog.cpp b/src/ifcviewer-full/ModelTransformationDialog.cpp
new file mode 100644
index 0000000000..f42c45ca42
--- /dev/null
+++ b/src/ifcviewer-full/ModelTransformationDialog.cpp
@@ -0,0 +1,248 @@
+/********************************************************************************
+ *                                                                              *
+ * This file is part of IfcOpenShell.                                           *
+ *                                                                              *
+ * IfcOpenShell is free software: you can redistribute it and/or modify         *
+ * it under the terms of the Lesser GNU General Public License as published by  *
+ * the Free Software Foundation, either version 3.0 of the License, or          *
+ * (at your option) any later version.                                          *
+ *                                                                              *
+ * IfcOpenShell is distributed in the hope that it will be useful,              *
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of               *
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the                 *
+ * Lesser GNU General Public License for more details.                          *
+ *                                                                              *
+ * You should have received a copy of the Lesser GNU General Public License     *
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.         *
+ *                                                                              *
+ ********************************************************************************/
+
+#include "ModelTransformationDialog.h"
+#include "Federation.h"
+
+#include <QButtonGroup>
+#include <QComboBox>
+#include <QDialogButtonBox>
+#include <QDoubleSpinBox>
+#include <QFormLayout>
+#include <QGroupBox>
+#include <QHBoxLayout>
+#include <QLabel>
+#include <QRadioButton>
+#include <QShowEvent>
+#include <QVBoxLayout>
+
+namespace {
+
+QString unitDisplay(const FederationConfig& cfg) {
+    QString s;
+    if (!cfg.unit_prefix.empty()) s += QString::fromStdString(cfg.unit_prefix) + " ";
+    s += QString::fromStdString(cfg.unit_name);
+    return s;
+}
+
+}  // namespace
+
+ModelTransformationDialog::ModelTransformationDialog(Federation* federation,
+                                                     QWidget* parent)
+    : QDialog(parent), federation_(federation)
+{
+    setWindowTitle("Model Transformation");
+    setupUi();
+}
+
+void ModelTransformationDialog::setupUi() {
+    auto* root = new QVBoxLayout(this);
+
+    // Model picker.
+    {
+        auto* row = new QHBoxLayout();
+        row->addWidget(new QLabel("Model:", this));
+        model_combo_ = new QComboBox(this);
+        row->addWidget(model_combo_, 1);
+        root->addLayout(row);
+        connect(model_combo_, QOverload<int>::of(&QComboBox::currentIndexChanged),
+                this, &ModelTransformationDialog::onModelChanged);
+    }
+
+    auto build_xyz = [](QDoubleSpinBox*& sb) {
+        sb = new QDoubleSpinBox();
+        sb->setRange(-1e12, 1e12);
+        sb->setDecimals(6);
+        sb->setSingleStep(1.0);
+    };
+
+    // A-frame + A.
+    {
+        auto* group = new QGroupBox("Point A", this);
+        group->setToolTip(
+            "The model-side anchor point.  ModelLocal expresses A in the "
+            "model's project length unit, before its CoordinateOperation.  "
+            "ModelGlobal expresses A in the model's map unit, after its "
+            "CoordinateOperation.");
+        auto* form = new QFormLayout(group);
+
+        radio_local_  = new QRadioButton("ModelLocal", group);
+        radio_global_ = new QRadioButton("ModelGlobal", group);
+        radio_global_->setChecked(true);
+        auto* af_group = new QButtonGroup(this);
+        af_group->addButton(radio_local_);
+        af_group->addButton(radio_global_);
+        connect(radio_local_,  &QRadioButton::toggled,
+                this, &ModelTransformationDialog::onAFrameToggled);
+        connect(radio_global_, &QRadioButton::toggled,
+                this, &ModelTransformationDialog::onAFrameToggled);
+
+        auto* af_row = new QHBoxLayout();
+        af_row->addWidget(radio_local_);
+        af_row->addWidget(radio_global_);
+        af_row->addStretch();
+        form->addRow("Frame", af_row);
+
+        build_xyz(a_x_); build_xyz(a_y_); build_xyz(a_z_);
+        form->addRow("X", a_x_);
+        form->addRow("Y", a_y_);
+        form->addRow("Z", a_z_);
+        a_unit_label_ = new QLabel("(model unit)", group);
+        form->addRow("Unit", a_unit_label_);
+
+        root->addWidget(group);
+    }
+
+    // B.
+    {
+        auto* group = new QGroupBox("Point B (federation target)", this);
+        group->setToolTip(
+            "Where in the federation point A should land.  In federation units.");
+        auto* form = new QFormLayout(group);
+        build_xyz(b_x_); build_xyz(b_y_); build_xyz(b_z_);
+        form->addRow("X", b_x_);
+        form->addRow("Y", b_y_);
+        form->addRow("Z", b_z_);
+        b_unit_label_ = new QLabel("(federation unit)", group);
+        form->addRow("Unit", b_unit_label_);
+        root->addWidget(group);
+    }
+
+    // Rotation (intrinsic XYZ).
+    {
+        auto* group = new QGroupBox("Rotation (intrinsic XYZ, degrees)", this);
+        group->setToolTip(
+            "Composed as R = R_z(rz) · R_y(ry) · R_x(rx).  Y-up models "
+            "rotated to Z-up: rx = 90, ry = 0, rz = 0.");
+        auto* form = new QFormLayout(group);
+        rx_ = new QDoubleSpinBox(); rx_->setRange(-360, 360); rx_->setDecimals(6);
+        ry_ = new QDoubleSpinBox(); ry_->setRange(-360, 360); ry_->setDecimals(6);
+        rz_ = new QDoubleSpinBox(); rz_->setRange(-360, 360); rz_->setDecimals(6);
+        form->addRow("rx (°)", rx_);
+        form->addRow("ry (°)", ry_);
+        form->addRow("rz (°)", rz_);
+        root->addWidget(group);
+    }
+
+    // Pivot.
+    {
+        auto* group = new QGroupBox("Rotation Pivot", this);
+        group->setToolTip(
+            "The point the rotation rotates around, in federation units.  "
+            "Set pivot = B to keep A landing on B regardless of rotation.");
+        auto* form = new QFormLayout(group);
+        build_xyz(pivot_x_); build_xyz(pivot_y_); build_xyz(pivot_z_);
+        form->addRow("X", pivot_x_);
+        form->addRow("Y", pivot_y_);
+        form->addRow("Z", pivot_z_);
+        pivot_unit_label_ = new QLabel("(federation unit)", group);
+        form->addRow("Unit", pivot_unit_label_);
+        root->addWidget(group);
+    }
+
+    auto* button_box = new QDialogButtonBox(
+        QDialogButtonBox::Ok | QDialogButtonBox::Cancel, this);
+    root->addWidget(button_box);
+    connect(button_box, &QDialogButtonBox::accepted, this,
+            &ModelTransformationDialog::onAccepted);
+    connect(button_box, &QDialogButtonBox::rejected, this, &QDialog::reject);
+}
+
+void ModelTransformationDialog::showEvent(QShowEvent* event) {
+    populateModelCombo();
+    refreshUnitLabels();
+    if (model_combo_->count() > 0) {
+        syncFromModel(model_combo_->currentData().toString());
+    }
+    QDialog::showEvent(event);
+}
+
+void ModelTransformationDialog::populateModelCombo() {
+    model_combo_->blockSignals(true);
+    QString prev_id = model_combo_->currentData().toString();
+    model_combo_->clear();
+    if (federation_) {
+        for (const auto& m : federation_->models()) {
+            QString label = m.display_name.isEmpty() ? m.id : m.display_name;
+            model_combo_->addItem(label, m.id);
+        }
+    }
+    int restore = -1;
+    for (int i = 0; i < model_combo_->count(); ++i) {
+        if (model_combo_->itemData(i).toString() == prev_id) { restore = i; break; }
+    }
+    if (restore >= 0) model_combo_->setCurrentIndex(restore);
+    model_combo_->blockSignals(false);
+}
+
+void ModelTransformationDialog::syncFromModel(const QString& fed_id) {
+    if (!federation_) return;
+    const Federation::Model* m = federation_->findById(fed_id);
+    if (!m) return;
+    const ModelTransformation& xf = m->model_transformation;
+
+    radio_local_->setChecked(xf.a_frame == AFrame::ModelLocal);
+    radio_global_->setChecked(xf.a_frame == AFrame::ModelGlobal);
+
+    a_x_->setValue(xf.a.x()); a_y_->setValue(xf.a.y()); a_z_->setValue(xf.a.z());
+    b_x_->setValue(xf.b.x()); b_y_->setValue(xf.b.y()); b_z_->setValue(xf.b.z());
+    rx_->setValue(xf.rxyz_deg.x());
+    ry_->setValue(xf.rxyz_deg.y());
+    rz_->setValue(xf.rxyz_deg.z());
+    pivot_x_->setValue(xf.pivot.x());
+    pivot_y_->setValue(xf.pivot.y());
+    pivot_z_->setValue(xf.pivot.z());
+}
+
+void ModelTransformationDialog::refreshUnitLabels() {
+    if (!federation_) return;
+    const QString fed_unit = unitDisplay(federation_->config());
+    b_unit_label_->setText("(federation: " + fed_unit + ")");
+    pivot_unit_label_->setText("(federation: " + fed_unit + ")");
+    onAFrameToggled();
+}
+
+void ModelTransformationDialog::onModelChanged(int /*idx*/) {
+    if (model_combo_->count() == 0) return;
+    syncFromModel(model_combo_->currentData().toString());
+}
+
+void ModelTransformationDialog::onAFrameToggled() {
+    if (!a_unit_label_) return;
+    if (radio_local_->isChecked()) {
+        a_unit_label_->setText("(model project length unit, e.g. millimetre)");
+    } else {
+        a_unit_label_->setText("(model map unit, e.g. metre)");
+    }
+}
+
+void ModelTransformationDialog::onAccepted() {
+    if (!federation_ || model_combo_->count() == 0) { accept(); return; }
+    const QString fed_id = model_combo_->currentData().toString();
+
+    ModelTransformation xf;
+    xf.a_frame  = radio_local_->isChecked() ? AFrame::ModelLocal : AFrame::ModelGlobal;
+    xf.a        = Eigen::Vector3d(a_x_->value(),     a_y_->value(),     a_z_->value());
+    xf.b        = Eigen::Vector3d(b_x_->value(),     b_y_->value(),     b_z_->value());
+    xf.rxyz_deg = Eigen::Vector3d(rx_->value(),      ry_->value(),      rz_->value());
+    xf.pivot    = Eigen::Vector3d(pivot_x_->value(), pivot_y_->value(), pivot_z_->value());
+
+    federation_->setModelTransformation(fed_id, xf);
+    accept();
+}
diff --git a/src/ifcviewer-full/ModelTransformationDialog.h b/src/ifcviewer-full/ModelTransformationDialog.h
new file mode 100644
index 0000000000..1d4d910095
--- /dev/null
+++ b/src/ifcviewer-full/ModelTransformationDialog.h
@@ -0,0 +1,88 @@
+/********************************************************************************
+ *                                                                              *
+ * This file is part of IfcOpenShell.                                           *
+ *                                                                              *
+ * IfcOpenShell is free software: you can redistribute it and/or modify         *
+ * it under the terms of the Lesser GNU General Public License as published by  *
+ * the Free Software Foundation, either version 3.0 of the License, or          *
+ * (at your option) any later version.                                          *
+ *                                                                              *
+ * IfcOpenShell is distributed in the hope that it will be useful,              *
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of               *
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the                 *
+ * Lesser GNU General Public License for more details.                          *
+ *                                                                              *
+ * You should have received a copy of the Lesser GNU General Public License     *
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.         *
+ *                                                                              *
+ ********************************************************************************/
+
+#ifndef MODELTRANSFORMATIONDIALOG_H
+#define MODELTRANSFORMATIONDIALOG_H
+
+#include <QDialog>
+#include <QString>
+
+QT_BEGIN_NAMESPACE
+class QComboBox;
+class QDoubleSpinBox;
+class QLabel;
+class QRadioButton;
+QT_END_NAMESPACE
+
+class Federation;
+
+// Edits one model's ModelTransformation (the per-model placement within
+// the federation: a_frame, a, b, rxyz Euler degrees, pivot).  A combobox
+// at the top picks which model to edit.  Switching models discards any
+// unsaved form edits — Ok saves the currently-visible model.  On Ok,
+// calls Federation::setModelTransformation, which fires
+// modelTransformationChanged → MainWindow recomposes the viewport for
+// that model.
+class ModelTransformationDialog : public QDialog {
+    Q_OBJECT
+public:
+    explicit ModelTransformationDialog(Federation* federation, QWidget* parent = nullptr);
+
+protected:
+    void showEvent(QShowEvent* event) override;
+
+private slots:
+    void onModelChanged(int idx);
+    void onAFrameToggled();
+    void onAccepted();
+
+private:
+    void setupUi();
+    void populateModelCombo();
+    void syncFromModel(const QString& fed_id);
+    void refreshUnitLabels();
+
+    Federation* federation_ = nullptr;
+
+    QComboBox*    model_combo_ = nullptr;
+
+    QRadioButton* radio_local_  = nullptr;
+    QRadioButton* radio_global_ = nullptr;
+
+    QDoubleSpinBox* a_x_ = nullptr;
+    QDoubleSpinBox* a_y_ = nullptr;
+    QDoubleSpinBox* a_z_ = nullptr;
+    QLabel*         a_unit_label_ = nullptr;
+
+    QDoubleSpinBox* b_x_ = nullptr;
+    QDoubleSpinBox* b_y_ = nullptr;
+    QDoubleSpinBox* b_z_ = nullptr;
+    QLabel*         b_unit_label_ = nullptr;
+
+    QDoubleSpinBox* rx_ = nullptr;
+    QDoubleSpinBox* ry_ = nullptr;
+    QDoubleSpinBox* rz_ = nullptr;
+
+    QDoubleSpinBox* pivot_x_ = nullptr;
+    QDoubleSpinBox* pivot_y_ = nullptr;
+    QDoubleSpinBox* pivot_z_ = nullptr;
+    QLabel*         pivot_unit_label_ = nullptr;
+};
+
+#endif