# Model Generation : 3D Marker Models with Horos 1. Open Horos 2. Under Patient Name in the opening screen, select the CT model you are working on, and click **2D viewer**.\ ![](/files/-M-QIYTalY5YHyrxHXyh) 3. Select the gear button (which reads 2D/3D underneath) and choose **3D surface rendering**.\ ![](/files/-M-QIYTb7lc9k3FQ-1we) 4. Under Predefined Values, choose **CT - Metal**\ ![](/files/-M-QIYT_l6RIyY22n_uP) 5. Select **OK** 6. Only your markers should appear in the view. You can toggle the view using the Mouse button functions at the top left corner of the screen. 7. If the model seems messy (there are dots that don't appear to be markers, or some of the markers appear to be missing or have large dents in them), you can select **Surface Settings** and modify the **Pixel Values**. 8. When you are finished, select the gear button that reads **Export 3D-SR** underneath, and choose **Export as Wavefront (.obj)**\ ![](/files/-M-QIYTZLViGz4RB97BB) 9. This is typically named something similar to 3DFile\_MarkerModel. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://gitbook.brown.edu/xromm/model-generation/xromm-3d-marker-models.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.