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Messages - Nathan Craig

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General / Image Textures for Exported Files
« on: July 24, 2010, 07:53:44 PM »
Creating a textured mesh with PhotoScan is a real snap. Often times, I want to export a model to another program for further processing. Registering more than one mesh is a common example of these additional processing requirements.

I have exported from PhotoScan models that are in the ply, obj, and 3ds formats. My real preference is for ply. When I open any of these files (ply, obj, 3ds) only the mesh opens in the external program. So far I have used MeshLab (which was suggested on a separate thread of this website) and VRMesh Studio. When I open an exported ply file, there is no texture displayed in either MeshLab or VRMesh Studio. I see that PhotoScan creates a jpg texture file, but for some reason this does not seem to be linked to the mesh in other programs. Can you give me any suggestions as to how I can open in MeshLab a textured mesh created in PhotoScan?

Any help on this front would be greatly appreciated.

General / Re: Re: Image Collection Limits
« on: July 24, 2010, 07:48:18 PM »
Dear Dmitry,

Thank you for your detailed response. This will help me configure equipment that is most efficient for processing image collections with PhotoScaner. I am presently in the field, internet access is intermittent, and access to new hardware impossible. When I return to the US, I'll be looking into installing PhotoScaner on a high end Win64. I've got a pair of machines in my lab that would be perfect. In the mean time, I seem to be able to regularly process collections of >30 4 megapixel images. I'm considering downsampling a little more to see if that will permit more images to be included in the collections. In the mean time I have been working with the following process:

Select 25-30 images that are on a single "flight line" and process these images. Once the mesh and photo texture is created, I export this as a ply file. Then I process the next 25-30 images. I often leave an overlap of 2-5 images to ensure that both sections will have enough common form to permit co-registration.

When I open a pair of ply files created from different image sub-sets the scale in the two models looks "pretty close". In VRMesh Studio, I use a manual registration routine and then perform a global registration between the two sections. I've not tried registering two sections in MeshLab, but this is on my list of things to try.

The ability to process 100 images with 64 bit OS would be fantastic. That would significantly reduce the number of sections that have to be registered.

Do you have any suggestions to ensuring that the scale is similar in different sets of sub-collections? Given the way I place targets, I can't always be sure there are two separate known points for setting scale. If there are processing parameters that would help ensure common scale across sub-sets of a larger collection, I would be very interested to learn about this.

Thanks again, I've already been getting good use out of PhotoScan.

General / Image Collection Limits
« on: July 22, 2010, 07:00:44 AM »
From a thread on a kite aerial photography (KAP) discussion board, I just learned of PhotoScan ( I am an archaeologist using KAP to photograph and document large sites. I have been working with several structure from motion (SfM)packages including Photosynth, Bundler, and Photocity. Today, I downloaded the PhotoScan demo and was extremely impressed. It looks like PhotoScan will serve my needs very well, and I just purchased an educational license of the PhotoScan.

For recording archaeological sites with KAP, I focus on straight down "ortho" photographs. I generally use a gyro-stabilized rig, and I freuqntly produce planar panoramas consisting of over a hundred images. Many of the sites in Peru that I am recording with KAP are greater than 10 ha. Thus, my requirements for SfM involves processing image collections of several hundred photographs. Using PhotoScan, I have processed collections of over 40 images but have not yet attempted a collection of more than a hundred images.

I am curious as to what are the limiting factors on the size of image collections that can be processed. By this I mean how many images can I expect to process, and what are the specific limiting factors for the number of images that can be processed? Are there hardware configurations that would facilitate or permit the processing of more images? Are there software or operating system "caps" that prevent processing collections of more than some number of images or perhaps better stated as total number of pixels?

Based on my initial tests, it appears that 4 megapixel images produce very good results. With a hypothetical size of 4 megapixel images, how might I go about calculating the maximum size of image collections that I can process. My interests are in using a machine that will maximize the number of images that can be processed. Any insight into these issues would be greatly appreciated.

Thank you,

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