diff --git a/CMakeLists.txt b/CMakeLists.txt
index b8cc777..165c435 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -289,6 +289,7 @@ set(PUBLICHEADERS
     include/aare/File.hpp
     include/aare/FileInterface.hpp
     include/aare/Frame.hpp
+    include/aare/geo_helpers.hpp
     include/aare/NDArray.hpp
     include/aare/NDView.hpp
     include/aare/NumpyFile.hpp
@@ -311,6 +312,7 @@ set(SourceFiles
     ${CMAKE_CURRENT_SOURCE_DIR}/src/decode.cpp
     ${CMAKE_CURRENT_SOURCE_DIR}/src/Frame.cpp
     ${CMAKE_CURRENT_SOURCE_DIR}/src/File.cpp
+    ${CMAKE_CURRENT_SOURCE_DIR}/src/geo_helpers.cpp
     ${CMAKE_CURRENT_SOURCE_DIR}/src/NumpyFile.cpp
     ${CMAKE_CURRENT_SOURCE_DIR}/src/NumpyHelpers.cpp
     ${CMAKE_CURRENT_SOURCE_DIR}/src/PixelMap.cpp
@@ -352,6 +354,7 @@ if(AARE_TESTS)
             ${CMAKE_CURRENT_SOURCE_DIR}/src/defs.test.cpp
             ${CMAKE_CURRENT_SOURCE_DIR}/src/Dtype.test.cpp
             ${CMAKE_CURRENT_SOURCE_DIR}/src/Frame.test.cpp
+            ${CMAKE_CURRENT_SOURCE_DIR}/src/geo_helpers.test.cpp
             ${CMAKE_CURRENT_SOURCE_DIR}/src/RawMasterFile.test.cpp
             ${CMAKE_CURRENT_SOURCE_DIR}/src/NDArray.test.cpp
             ${CMAKE_CURRENT_SOURCE_DIR}/src/NDView.test.cpp
diff --git a/include/aare/RawFile.hpp b/include/aare/RawFile.hpp
index eb044e3..f744ac2 100644
--- a/include/aare/RawFile.hpp
+++ b/include/aare/RawFile.hpp
@@ -34,15 +34,19 @@ class RawFile : public FileInterface {
     size_t n_subfile_parts{}; // d0,d1...dn
     //TODO! move to vector of SubFile instead of pointers
     std::vector<std::vector<RawSubFile *>> subfiles; //subfiles[f0,f1...fn][d0,d1...dn]
-    std::vector<xy> positions;
-    std::vector<ModuleGeometry> m_module_pixel_0;
+    // std::vector<xy> positions;
+    
     ModuleConfig cfg{0, 0};
 
     RawMasterFile m_master;
 
     size_t m_current_frame{};
-    size_t m_rows{};
-    size_t m_cols{};
+
+    // std::vector<ModuleGeometry> m_module_pixel_0;
+    // size_t m_rows{};
+    // size_t m_cols{};
+
+    DetectorGeometry m_geometry;
 
   public:
     /**
@@ -111,11 +115,12 @@ class RawFile : public FileInterface {
      */
     static DetectorHeader read_header(const std::filesystem::path &fname);
 
-    void update_geometry_with_roi();
+    // void update_geometry_with_roi();
     int find_number_of_subfiles();
 
     void open_subfiles();
     void find_geometry();
 };
 
+
 } // namespace aare
\ No newline at end of file
diff --git a/include/aare/RawMasterFile.hpp b/include/aare/RawMasterFile.hpp
index 42c324e..beaeb29 100644
--- a/include/aare/RawMasterFile.hpp
+++ b/include/aare/RawMasterFile.hpp
@@ -62,17 +62,6 @@ class ScanParameters {
 };
 
 
-struct ROI{
-  int64_t xmin{};
-  int64_t xmax{};
-  int64_t ymin{};
-  int64_t ymax{};
-
-  int64_t height() const { return ymax - ymin; }
-  int64_t width() const { return xmax - xmin; }
-};
-
-
 /**
  * @brief Class for parsing a master file either in our .json format or the old
  * .raw format
diff --git a/include/aare/defs.hpp b/include/aare/defs.hpp
index 7466410..db1a47b 100644
--- a/include/aare/defs.hpp
+++ b/include/aare/defs.hpp
@@ -179,13 +179,42 @@ template <typename T> struct t_xy {
 using xy = t_xy<uint32_t>;
 
 
+/**
+ * @brief Class to hold the geometry of a module. Where pixel 0 is located and the size of the module
+ */
 struct ModuleGeometry{
-    int x{};
-    int y{};
+    int origin_x{};
+    int origin_y{};
     int height{};
     int width{};
+    int row_index{};
+    int col_index{}; 
 };
 
+/**
+ * @brief Class to hold the geometry of a detector. Number of modules, their size and where pixel 0 
+ * for each module is located
+ */
+struct DetectorGeometry{
+    int modules_x{};
+    int modules_y{};
+    int pixels_x{};
+    int pixels_y{};
+    int module_gap_row{};
+    int module_gap_col{};
+    std::vector<ModuleGeometry> module_pixel_0;
+};
+
+struct ROI{
+    int64_t xmin{};
+    int64_t xmax{};
+    int64_t ymin{};
+    int64_t ymax{};
+  
+    int64_t height() const { return ymax - ymin; }
+    int64_t width() const { return xmax - xmin; }
+  };
+
 
 using dynamic_shape = std::vector<int64_t>;
 
diff --git a/include/aare/geo_helpers.hpp b/include/aare/geo_helpers.hpp
new file mode 100644
index 0000000..d0d5d1a
--- /dev/null
+++ b/include/aare/geo_helpers.hpp
@@ -0,0 +1,16 @@
+#pragma once
+#include "aare/defs.hpp"
+#include "aare/RawMasterFile.hpp" //ROI refactor away
+namespace aare{
+
+/**
+ * @brief Update the detector geometry given a region of interest
+ * 
+ * @param geo 
+ * @param roi 
+ * @return DetectorGeometry 
+ */
+DetectorGeometry update_geometry_with_roi(DetectorGeometry geo, ROI roi);
+
+
+} // namespace aare
\ No newline at end of file
diff --git a/python/examples/play.py b/python/examples/play.py
index 25bbe12..316c196 100644
--- a/python/examples/play.py
+++ b/python/examples/play.py
@@ -8,13 +8,15 @@ import numpy as np
 import boost_histogram as bh
 import time
 
-from aare import File, ClusterFinder, VarClusterFinder, ClusterFile
+from aare import RawFile
 
-base = Path('/mnt/sls_det_storage/matterhorn_data/aare_test_data/ci/aare_test_data/clusters/')
+f = RawFile('/mnt/sls_det_storage/jungfrau_data1/vadym_tests/jf12_M431/laser_scan/laserScan_pedestal_G0_master_0.json')
 
-f = ClusterFile(base/'beam_En700eV_-40deg_300V_10us_d0_f0_100.clust')
+print(f'{f.frame_number(1)}')
 
-c = f.read_clusters(100)
+for i in range(10):
+    header, img = f.read_frame()
+    print(header['frameNumber'], img.shape)
 
 # for i, frame in enumerate(f):
 #     print(f'{i}', end='\r')
diff --git a/src/RawFile.cpp b/src/RawFile.cpp
index b8c49cf..ef622ee 100644
--- a/src/RawFile.cpp
+++ b/src/RawFile.cpp
@@ -1,6 +1,7 @@
 #include "aare/RawFile.hpp"
 #include "aare/PixelMap.hpp"
 #include "aare/defs.hpp"
+#include "aare/geo_helpers.hpp"
 
 #include <fmt/format.h>
 #include <nlohmann/json.hpp>
@@ -21,8 +22,11 @@ RawFile::RawFile(const std::filesystem::path &fname, const std::string &mode)
         
 
         find_geometry();
-        update_geometry_with_roi();
 
+        if (m_master.roi()){
+            m_geometry = update_geometry_with_roi(m_geometry, m_master.roi().value());
+        }
+        
         open_subfiles();
     } else {
         throw std::runtime_error(LOCATION +
@@ -72,9 +76,13 @@ size_t RawFile::n_mod() const { return n_subfile_parts; }
 
 
 size_t RawFile::bytes_per_frame() {
-    return m_rows * m_cols * m_master.bitdepth() / 8;
+    // return m_rows * m_cols * m_master.bitdepth() / 8;
+    return m_geometry.pixels_x * m_geometry.pixels_y * m_master.bitdepth() / 8;
+}
+size_t RawFile::pixels_per_frame() { 
+    // return m_rows * m_cols; 
+    return m_geometry.pixels_x * m_geometry.pixels_y;
 }
-size_t RawFile::pixels_per_frame() { return m_rows * m_cols; }
 
 DetectorType RawFile::detector_type() const { return m_master.detector_type(); }
 
@@ -92,8 +100,8 @@ void RawFile::seek(size_t frame_index) {
 size_t RawFile::tell() { return m_current_frame; };
 
 size_t RawFile::total_frames() const { return m_master.frames_in_file(); }
-size_t RawFile::rows() const { return m_rows; }
-size_t RawFile::cols() const { return m_cols; }
+size_t RawFile::rows() const { return m_geometry.pixels_y; }
+size_t RawFile::cols() const { return m_geometry.pixels_x; }
 size_t RawFile::bitdepth() const { return m_master.bitdepth(); }
 xy RawFile::geometry() { return m_master.geometry(); }
 
@@ -102,11 +110,12 @@ void RawFile::open_subfiles() {
         for (size_t i = 0; i != n_subfiles; ++i) {
             auto v = std::vector<RawSubFile *>(n_subfile_parts);
             for (size_t j = 0; j != n_subfile_parts; ++j) {
-                auto pos = m_module_pixel_0[j];
+                auto pos = m_geometry.module_pixel_0[j];
+                fmt::println("POS: {} {} {} {}", pos.origin_x, pos.origin_y, pos.width, pos.height);
                 v[j] = new RawSubFile(m_master.data_fname(j, i),
                                       m_master.detector_type(), pos.height,
                                       pos.width, m_master.bitdepth(),
-                                      positions[j].row, positions[j].col);
+                                      pos.row_index, pos.col_index);
 
             }
             subfiles.push_back(v);
@@ -149,112 +158,49 @@ int RawFile::find_number_of_subfiles() {
 
 RawMasterFile RawFile::master() const { return m_master; }
 
+/**
+ * @brief Find the geometry of the detector by opening all the subfiles and
+ * reading the headers. 
+ */
 void RawFile::find_geometry() {
+    
+    //Hold the maximal row and column number found
+    //Later used for calculating the total number of rows and columns
     uint16_t r{};
     uint16_t c{};
 
 
     for (size_t i = 0; i < n_subfile_parts; i++) {
-        auto h = this->read_header(m_master.data_fname(i, 0));
+        auto h = read_header(m_master.data_fname(i, 0));
         r = std::max(r, h.row);
         c = std::max(c, h.column);
-        positions.push_back({h.row, h.column});
+        // positions.push_back({h.row, h.column});
+       
         ModuleGeometry g;
-        g.x = h.column * m_master.pixels_x();
-        g.y = h.row * m_master.pixels_y();
+        g.origin_x = h.column * m_master.pixels_x();
+        g.origin_y = h.row * m_master.pixels_y();
+        g.row_index = h.row;
+        g.col_index = h.column;
         g.width = m_master.pixels_x();
         g.height = m_master.pixels_y();
-        m_module_pixel_0.push_back(g);
+        m_geometry.module_pixel_0.push_back(g);
 
     }
 
     r++;
     c++;
 
-    m_rows = (r * m_master.pixels_y());
-    m_cols = (c * m_master.pixels_x());
-
-    m_rows += static_cast<size_t>((r - 1) * cfg.module_gap_row);
-
-#ifdef AARE_VERBOSE
-    fmt::print("\nRawFile::find_geometry()\n");
-    for (size_t i = 0; i < m_module_pixel_0.size(); i++) {
-        fmt::print("Module {} at position: (r:{},c:{})\n", i,
-                   m_module_pixel_0[i].y, m_module_pixel_0[i].x);
-    }
-    fmt::print("Image size: {}x{}\n\n", m_rows, m_cols);
-#endif
-}
-
-void RawFile::update_geometry_with_roi() {
-    // TODO! implement this
-    if (m_master.roi()) {
-        auto roi = m_master.roi().value();
-
-        // TODO! can we do this cleaner?
-        int pos_y = 0;
-        int pos_y_increment = 0;
-        for (size_t row = 0; row < m_master.geometry().row; row++) {
-            int pos_x = 0;
-            for (size_t col = 0; col < m_master.geometry().col; col++) {
-                auto &m = m_module_pixel_0[row * m_master.geometry().col + col];
-                auto original_height = m.height;
-                auto original_width = m.width;
-
-                // module is to the left of the roi
-                if (m.x + m.width < roi.xmin) {
-                    m.width = 0;
-
-                    // roi is in module
-                } else {
-                    // here we only arrive when the roi is in or to the left of
-                    // the module
-                    if (roi.xmin > m.x) {
-                        m.width -= roi.xmin - m.x;
-                    }
-                    if (roi.xmax < m.x + m.width) {
-                        m.width -= m.x + original_width - roi.xmax;
-                    }
-                    m.x = pos_x;
-                    pos_x += m.width;
-                }
-
-                if (m.y + m.height < roi.ymin) {
-                    m.height = 0;
-                } else {
-                    if ((roi.ymin > m.y) && (roi.ymin < m.y + m.height)) {
-                        m.height -= roi.ymin - m.y;
-
-                    }
-                    if (roi.ymax < m.y + m.height) {
-                        m.height -= m.y + original_height - roi.ymax;
-                    }
-                    m.y = pos_y;
-                    pos_y_increment = m.height;
-                }
-            }
-            // increment pos_y
-            pos_y += pos_y_increment;
-        }
-
-        m_rows = roi.height();
-        m_cols = roi.width();
-    }
-
-#ifdef AARE_VERBOSE
-    fmt::print("RawFile::update_geometry_with_roi()\n");
-    for (const auto &m : m_module_pixel_0) {
-        fmt::print("Module at position: (r:{}, c:{}, h:{}, w:{})\n", m.y, m.x,
-                   m.height, m.width);
-    }
-    fmt::print("Updated image size: {}x{}\n\n", m_rows, m_cols);
-    fmt::print("\n");
-#endif
+    m_geometry.pixels_y = (r * m_master.pixels_y());
+    m_geometry.pixels_x  = (c * m_master.pixels_x());
+    m_geometry.modules_x = c;
+    m_geometry.modules_y = r;
+    m_geometry.pixels_y += static_cast<size_t>((r - 1) * cfg.module_gap_row);
 
 }
 
+
 Frame RawFile::get_frame(size_t frame_index) {
-    auto f = Frame(m_rows, m_cols, Dtype::from_bitdepth(m_master.bitdepth()));
+    auto f = Frame(m_geometry.pixels_y, m_geometry.pixels_x, Dtype::from_bitdepth(m_master.bitdepth()));
     std::byte *frame_buffer = f.data();
     get_frame_into(frame_index, frame_buffer);
     return f;
@@ -321,10 +267,10 @@ void RawFile::get_frame_into(size_t frame_index, std::byte *frame_buffer, Detect
             }
 
             // This is where we start writing
-            auto offset = (m_module_pixel_0[part_idx].y * m_cols +
-                          m_module_pixel_0[part_idx].x)*m_master.bitdepth()/8;
+            auto offset = (m_geometry.module_pixel_0[part_idx].origin_y * m_geometry.pixels_x +
+                m_geometry.module_pixel_0[part_idx].origin_x)*m_master.bitdepth()/8;
 
-            if (m_module_pixel_0[part_idx].x!=0)
+            if (m_geometry.module_pixel_0[part_idx].origin_x!=0)
                 throw std::runtime_error(LOCATION + "Implementation error. x pos not 0.");
             
             //TODO! Risk for out of range access
@@ -348,7 +294,7 @@ void RawFile::get_frame_into(size_t frame_index, std::byte *frame_buffer, Detect
         // level
 
         for (size_t part_idx = 0; part_idx != n_subfile_parts; ++part_idx) {
-            auto pos = m_module_pixel_0[part_idx];
+            auto pos = m_geometry.module_pixel_0[part_idx];
             auto corrected_idx = frame_indices[part_idx];
             auto subfile_id = corrected_idx / m_master.max_frames_per_file();
             if (subfile_id >= subfiles.size()) {
@@ -364,9 +310,9 @@ void RawFile::get_frame_into(size_t frame_index, std::byte *frame_buffer, Detect
             for (size_t cur_row = 0; cur_row < static_cast<size_t>(pos.height);
                  cur_row++) {
 
-                auto irow = (pos.y + cur_row);
-                auto icol = pos.x;
-                auto dest = (irow * this->m_cols + icol);
+                auto irow = (pos.origin_y + cur_row);
+                auto icol = pos.origin_x;
+                auto dest = (irow * this->m_geometry.pixels_x + icol);
                 dest = dest * m_master.bitdepth() / 8;
                 memcpy(frame_buffer + dest,
                        part_buffer + cur_row * pos.width *
@@ -412,4 +358,8 @@ RawFile::~RawFile() {
     }
 }
 
+
+
+
+
 } // namespace aare
\ No newline at end of file
diff --git a/src/RawFile.test.cpp b/src/RawFile.test.cpp
index faefd28..5f9b2e1 100644
--- a/src/RawFile.test.cpp
+++ b/src/RawFile.test.cpp
@@ -1,10 +1,13 @@
 #include "aare/File.hpp"
+#include "aare/RawMasterFile.hpp" //needed for ROI
+#include "aare/RawFile.hpp"
 
 #include <catch2/catch_test_macros.hpp>
 #include <filesystem>
 
 #include "test_config.hpp"
 
+
 using aare::File;
 
 TEST_CASE("Read number of frames from a jungfrau raw file", "[.integration]") {
@@ -148,3 +151,5 @@ TEST_CASE("Read file with unordered frames", "[.integration]") {
     File f(fpath);
     REQUIRE_THROWS((f.read_frame()));
 }
+
+
diff --git a/src/RawSubFile.cpp b/src/RawSubFile.cpp
index 4612747..a3bb79c 100644
--- a/src/RawSubFile.cpp
+++ b/src/RawSubFile.cpp
@@ -44,7 +44,7 @@ RawSubFile::RawSubFile(const std::filesystem::path &fname,
 
 void RawSubFile::seek(size_t frame_index) {
     if (frame_index >= n_frames) {
-        throw std::runtime_error("Frame number out of range");
+        throw std::runtime_error(LOCATION + fmt::format("Frame index {} out of range in a file with {} frames", frame_index, n_frames));
     }
     m_file.seekg((sizeof(DetectorHeader) + bytes_per_frame()) * frame_index);
 }
diff --git a/src/geo_helpers.cpp b/src/geo_helpers.cpp
new file mode 100644
index 0000000..e823f22
--- /dev/null
+++ b/src/geo_helpers.cpp
@@ -0,0 +1,71 @@
+
+#include "aare/geo_helpers.hpp"
+#include "fmt/core.h"
+
+namespace aare{
+
+DetectorGeometry update_geometry_with_roi(DetectorGeometry geo, aare::ROI roi) {
+    #ifdef AARE_VERBOSE
+    fmt::println("update_geometry_with_roi() called with ROI: {} {} {} {}",
+                 roi.xmin, roi.xmax, roi.ymin, roi.ymax);
+    fmt::println("Geometry: {} {} {} {} {} {}",
+                 geo.modules_x, geo.modules_y, geo.pixels_x, geo.pixels_y, geo.module_gap_row, geo.module_gap_col);
+    #endif
+    int pos_y = 0;
+    int pos_y_increment = 0;
+    for (size_t row = 0; row < geo.modules_y; row++) {
+        int pos_x = 0;
+        for (size_t col = 0; col < geo.modules_x; col++) {
+            auto &m = geo.module_pixel_0[row * geo.modules_x + col];
+            auto original_height = m.height;
+            auto original_width = m.width;
+
+            // module is to the left of the roi
+            if (m.origin_x + m.width < roi.xmin) {
+                m.width = 0;
+
+                // roi is in module
+            } else {
+                // here we only arrive when the roi is in or to the left of
+                // the module
+                if (roi.xmin > m.origin_x) {
+                    m.width -= roi.xmin - m.origin_x;
+                }
+                if (roi.xmax < m.origin_x + original_width) {
+                    m.width -= m.origin_x + original_width - roi.xmax;
+                }
+                m.origin_x = pos_x;
+                pos_x += m.width;
+            }
+
+            if (m.origin_y + m.height < roi.ymin) {
+                m.height = 0;
+            } else {
+                if ((roi.ymin > m.origin_y) && (roi.ymin < m.origin_y + m.height)) {
+                    m.height -= roi.ymin - m.origin_y;
+
+                }
+                if (roi.ymax < m.origin_y + original_height) {
+                    m.height -= m.origin_y + original_height - roi.ymax;
+                }
+                m.origin_y = pos_y;
+                pos_y_increment = m.height;
+            }
+            #ifdef AARE_VERBOSE
+    fmt::println("Module {} {} {} {}", m.origin_x, m.origin_y, m.width, m.height);
+    #endif
+        }
+        // increment pos_y
+        pos_y += pos_y_increment;
+    }
+
+    // m_rows = roi.height();
+    // m_cols = roi.width();
+    geo.pixels_x = roi.width();
+    geo.pixels_y = roi.height();
+
+    return geo;
+
+}
+
+} // namespace aare
\ No newline at end of file
diff --git a/src/geo_helpers.test.cpp b/src/geo_helpers.test.cpp
new file mode 100644
index 0000000..08ee96c
--- /dev/null
+++ b/src/geo_helpers.test.cpp
@@ -0,0 +1,230 @@
+#include "aare/File.hpp"
+#include "aare/RawMasterFile.hpp" //needed for ROI
+#include "aare/RawFile.hpp"
+
+#include <catch2/catch_test_macros.hpp>
+#include <filesystem>
+
+#include "aare/geo_helpers.hpp"
+#include "test_config.hpp"
+
+TEST_CASE("Simple ROIs on one module"){
+    // DetectorGeometry update_geometry_with_roi(DetectorGeometry geo, aare::ROI roi)
+    aare::DetectorGeometry geo;
+    
+
+    aare::ModuleGeometry mod; 
+    mod.origin_x = 0;
+    mod.origin_y = 0;
+    mod.width = 1024;
+    mod.height = 512;
+
+
+    
+    geo.pixels_x = 1024;
+    geo.pixels_y = 512;
+    geo.modules_x = 1;
+    geo.modules_y = 1;
+    geo.module_pixel_0.push_back(mod);
+
+    SECTION("ROI is the whole module"){
+        aare::ROI roi;
+        roi.xmin = 0;
+        roi.xmax = 1024;
+        roi.ymin = 0;
+        roi.ymax = 512;
+        auto updated_geo = aare::update_geometry_with_roi(geo, roi);
+
+        REQUIRE(updated_geo.pixels_x == 1024);
+        REQUIRE(updated_geo.pixels_y == 512);
+        REQUIRE(updated_geo.modules_x == 1);
+        REQUIRE(updated_geo.modules_y == 1);
+        REQUIRE(updated_geo.module_pixel_0[0].height == 512);
+        REQUIRE(updated_geo.module_pixel_0[0].width == 1024);
+    }
+    SECTION("ROI is the top left corner of the module"){
+        aare::ROI roi;
+        roi.xmin = 100;
+        roi.xmax = 200;
+        roi.ymin = 150;
+        roi.ymax = 200;
+        auto updated_geo = aare::update_geometry_with_roi(geo, roi);
+
+        REQUIRE(updated_geo.pixels_x == 100);
+        REQUIRE(updated_geo.pixels_y == 50);
+        REQUIRE(updated_geo.modules_x == 1);
+        REQUIRE(updated_geo.modules_y == 1);
+        REQUIRE(updated_geo.module_pixel_0[0].height == 50);
+        REQUIRE(updated_geo.module_pixel_0[0].width == 100);
+    }
+
+    SECTION("ROI is a small square"){
+        aare::ROI roi;
+        roi.xmin = 1000;
+        roi.xmax = 1010;
+        roi.ymin = 500;
+        roi.ymax = 510;
+        auto updated_geo = aare::update_geometry_with_roi(geo, roi);
+
+        REQUIRE(updated_geo.pixels_x == 10);
+        REQUIRE(updated_geo.pixels_y == 10);
+        REQUIRE(updated_geo.modules_x == 1);
+        REQUIRE(updated_geo.modules_y == 1);
+        REQUIRE(updated_geo.module_pixel_0[0].height == 10);
+        REQUIRE(updated_geo.module_pixel_0[0].width == 10);
+    }
+    SECTION("ROI is a few columns"){
+        aare::ROI roi;
+        roi.xmin = 750;
+        roi.xmax = 800;
+        roi.ymin = 0;
+        roi.ymax = 512;
+        auto updated_geo = aare::update_geometry_with_roi(geo, roi);
+
+        REQUIRE(updated_geo.pixels_x == 50);
+        REQUIRE(updated_geo.pixels_y == 512);
+        REQUIRE(updated_geo.modules_x == 1);
+        REQUIRE(updated_geo.modules_y == 1);
+        REQUIRE(updated_geo.module_pixel_0[0].height == 512);
+        REQUIRE(updated_geo.module_pixel_0[0].width == 50);
+    }
+}
+
+
+
+TEST_CASE("Two modules side by side"){
+    // DetectorGeometry update_geometry_with_roi(DetectorGeometry geo, aare::ROI roi)
+    aare::DetectorGeometry geo;
+    
+
+    aare::ModuleGeometry mod; 
+    mod.origin_x = 0;
+    mod.origin_y = 0;
+    mod.width = 1024;
+    mod.height = 512;
+
+    geo.pixels_x = 2048;
+    geo.pixels_y = 512;
+    geo.modules_x = 2;
+    geo.modules_y = 1;
+
+    geo.module_pixel_0.push_back(mod);
+    mod.origin_x = 1024;
+    geo.module_pixel_0.push_back(mod);
+
+    SECTION("ROI is the whole image"){
+        aare::ROI roi;
+        roi.xmin = 0;
+        roi.xmax = 2048;
+        roi.ymin = 0;
+        roi.ymax = 512;
+        auto updated_geo = aare::update_geometry_with_roi(geo, roi);
+
+        REQUIRE(updated_geo.pixels_x == 2048);
+        REQUIRE(updated_geo.pixels_y == 512);
+        REQUIRE(updated_geo.modules_x == 2);
+        REQUIRE(updated_geo.modules_y == 1);
+    }
+    SECTION("rectangle on both modules"){
+        aare::ROI roi;
+        roi.xmin = 800;
+        roi.xmax = 1300;
+        roi.ymin = 200;
+        roi.ymax = 499;
+        auto updated_geo = aare::update_geometry_with_roi(geo, roi);
+
+        REQUIRE(updated_geo.pixels_x == 500);
+        REQUIRE(updated_geo.pixels_y == 299);
+        REQUIRE(updated_geo.modules_x == 2);
+        REQUIRE(updated_geo.modules_y == 1);
+        REQUIRE(updated_geo.module_pixel_0[0].height == 299);
+        REQUIRE(updated_geo.module_pixel_0[0].width == 224);
+        REQUIRE(updated_geo.module_pixel_0[1].height == 299);
+        REQUIRE(updated_geo.module_pixel_0[1].width == 276);
+    }   
+}
+
+TEST_CASE("Three modules side by side"){
+    // DetectorGeometry update_geometry_with_roi(DetectorGeometry geo, aare::ROI roi)
+    aare::DetectorGeometry geo;
+    aare::ROI roi;
+    roi.xmin = 700;
+    roi.xmax = 2500;
+    roi.ymin = 0;
+    roi.ymax = 123;
+
+    aare::ModuleGeometry mod; 
+    mod.origin_x = 0;
+    mod.origin_y = 0;
+    mod.width = 1024;
+    mod.height = 512;
+
+    geo.pixels_x = 3072;
+    geo.pixels_y = 512;
+    geo.modules_x = 3;
+    geo.modules_y = 1;
+
+    geo.module_pixel_0.push_back(mod);
+    mod.origin_x = 1024;
+    geo.module_pixel_0.push_back(mod);
+    mod.origin_x = 2048;
+    geo.module_pixel_0.push_back(mod);
+
+    auto updated_geo = aare::update_geometry_with_roi(geo, roi);
+
+    REQUIRE(updated_geo.pixels_x == 1800);
+    REQUIRE(updated_geo.pixels_y == 123);
+    REQUIRE(updated_geo.modules_x == 3);
+    REQUIRE(updated_geo.modules_y == 1);
+    REQUIRE(updated_geo.module_pixel_0[0].height == 123);
+    REQUIRE(updated_geo.module_pixel_0[0].width == 324);
+    REQUIRE(updated_geo.module_pixel_0[1].height == 123);
+    REQUIRE(updated_geo.module_pixel_0[1].width == 1024);
+    REQUIRE(updated_geo.module_pixel_0[2].height == 123);
+    REQUIRE(updated_geo.module_pixel_0[2].width == 452);
+}
+
+TEST_CASE("Four modules as a square"){
+    // DetectorGeometry update_geometry_with_roi(DetectorGeometry geo, aare::ROI roi)
+    aare::DetectorGeometry geo;
+    aare::ROI roi;
+    roi.xmin = 500;
+    roi.xmax = 2000;
+    roi.ymin = 500;
+    roi.ymax = 600;
+
+    aare::ModuleGeometry mod; 
+    mod.origin_x = 0;
+    mod.origin_y = 0;
+    mod.width = 1024;
+    mod.height = 512;
+
+    geo.pixels_x = 2048;
+    geo.pixels_y = 1024;
+    geo.modules_x = 2;
+    geo.modules_y = 2;
+
+    geo.module_pixel_0.push_back(mod);
+    mod.origin_x = 1024;
+    geo.module_pixel_0.push_back(mod);
+    mod.origin_x = 0;
+    mod.origin_y = 512;
+    geo.module_pixel_0.push_back(mod);
+    mod.origin_x = 1024;
+    geo.module_pixel_0.push_back(mod);
+
+    auto updated_geo = aare::update_geometry_with_roi(geo, roi);
+
+    REQUIRE(updated_geo.pixels_x == 1500);
+    REQUIRE(updated_geo.pixels_y == 100);
+    REQUIRE(updated_geo.modules_x == 2);
+    REQUIRE(updated_geo.modules_y == 2);
+    REQUIRE(updated_geo.module_pixel_0[0].height == 12);
+    REQUIRE(updated_geo.module_pixel_0[0].width == 524);
+    REQUIRE(updated_geo.module_pixel_0[1].height == 12);
+    REQUIRE(updated_geo.module_pixel_0[1].width == 976);
+    REQUIRE(updated_geo.module_pixel_0[2].height == 88);
+    REQUIRE(updated_geo.module_pixel_0[2].width == 524);
+    REQUIRE(updated_geo.module_pixel_0[3].height == 88);
+    REQUIRE(updated_geo.module_pixel_0[3].width == 976);
+}
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