added readme

README.md

@@ -3,4 +3,28 @@
 
 ## THD Json
 
-- Definitions of THD json format. Included: projections.
\ No newline at end of file
+### Projection
+
+| Property                      | Type     | Description                                             | Constraints               | Required |
+|-------------------------------|----------|---------------------------------------------------------|---------------------------|----------|
+| `focal_spot_position_mm`      | array    | Position of the focal spot in millimeters               | 3 numbers                 | Yes      |
+| `detector_center_position_mm` | array    | Center position of the detector in millimeters          | 3 numbers                 | Yes      |
+| `detector_horizontal_vector`  | array    | Horizontal orientation vector of the detector           | 3 numbers                 | Yes      |
+| `detector_vertical_vector`    | array    | Vertical orientation vector of the detector             | 3 numbers                 | Yes      |
+| `detector_center_orientation_quat` | array | Quaternion representing the detector's center orientation | 4 numbers               | Yes      |
+| `pixel_pitch_mm`              | number   | Pixel pitch in millimeters                              | -                         | Yes      |
+| `image_width_px`              | integer  | Width of the image in pixels                            | Minimum 1                 | Yes      |
+| `image_heigth_px`             | integer  | Height of the image in pixels                           | Minimum 1                 | Yes      |
+| `projection_matrix_cera`      | array    | Projection matrix for CERA, representing transformations | 3 arrays of 4 numbers    | No       |
+
+
+# Notes:
+- **Arrays**:
+  - `focal_spot_position_mm`, `detector_center_position_mm`, `detector_horizontal_vector`, `detector_vertical_vector`: Arrays containing exactly **3 numbers**.
+  - `detector_center_orientation_quat`: Array containing exactly **4 numbers**.
+  - `projection_matrix_cera`: Optional 3x4 matrix (array of 3 arrays, each with 4 numbers).
+
+- **Integers**:
+  - `image_width_px` and `image_heigth_px` have a minimum value constraint of 1.
+
+- **Additional Properties**: No additional properties are allowed outside of those defined here.