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PTM Dome Construction

Learn the minimum requirements for PTM dome construction, including lighting positions, creating a light position file, computer and software specifications, digital camera recommendations, and design considerations. Get insights on automation, software components, and additional resources.

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PTM Dome Construction

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  1. PTM Dome Construction

  2. Minimum Requirements • Repeatable Lighting locations • Recommend at least 50 positions • Light position file • Computer and PTM software • Digital camera

  3. Lighting Locations • Positions should be evenly distributed around hemisphere • 50 positions will evenly cover hemisphere • Additional positions give smoother transitions • Lighting sequence must be consistent

  4. Creating a Light Position File • Lighting positions measured in X, Y, Z coordinate system • Measurements converted to normalized vector values

  5. Conversion to Vector Value • Square root X2+Y2+Z2 • Divide X, Y, Z coordinates by this value to normalize • Calculate for each light position

  6. Light Position File • .txt file in column format • Image number and then normalized vector values • Image number must correspond the light position used to capture the image

  7. Computer • Modern computers are adequate • Recommend a minimum of 1GB RAM and 60GB storage space • Increased memory and graphics processing improves performance • Large image files require additional computing power and storage

  8. Software • PTM software runs through DOS • Two separate components to software • PTM Fitter • Fitter program is run separately after image capture • Creates .ptm file from images and LP file • Recognizes .jpg image format • PTM Viewer • Opens .ptm files for viewing

  9. Digital Camera • Position and settings must not be altered during image capture • SLR Style Camera • Sufficient resolution for application • Software development kit (SDK) • USB or IEEE connection if automating

  10. Automation • Camera shutter must be synchronized with lights. • Controller box built to fire and sequence flashes. • Modified camera SDK controls timing of lights and camera shutter • Images downloaded to designated folder

  11. Automation (cont.) • Simple .bat files created to number LP file and run PTM fitter program. • Image files could also be renamed to use with a static LP file. • Adobe Photoshop program allows batch processing of captured images. • Rename, Change file format, Crop, Resize, etc.

  12. Design Considerations • Light output determines radius of hemisphere • Brighter flashes need more distance (radius) from object • Radius of hemisphere determines overall size • Camera positioning • Distance/focal length combination

  13. Design Considerations (cont.) • Crime Scene use • Mobility • Contact area • Weather • Power • Clean up

  14. Additional Information • http://www.hpl.hp.com/research/ptm/ri.html • Reflectance Imaging • http://www.hpl.hp.com/research/ptm/se.html • Reflectance Transformation • http://palaeo-electronica.org/2002_1/fossils/issue1_02.htm • Paper on Fossil imaging using PTM technique • http://www.hpl.hp.com/personal/Tom_Malzbender/papers/egrw2006.pdf • Paper on surface enhancement with PTM technique.

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