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Topics - Nathan Craig

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Camera Calibration / Use of Macro setting when calibrating a lens
« on: June 24, 2011, 05:59:37 PM »
Most of the images I process in PhotoScan are taken from a kite and the lens is focused at infinity. To calibrate a lens using PHotoScan Lens, I must move the camera close to the computer monitor. So close in fact, that I must use the camera's macro function. Should I expect the use of a different mode to have a significant impact on lens calibration?


At present, PhotoScan can display EXIF data (like camera and focal length) that are relevant to selecting the appropriate calibration. The calibration input interface permits the input of specific calibrations. For projects that use multiple cameras or focal lengths, it would greatly streamline the selection of the correct calibration files to have the relevant EXIF data also displayed in the calibration input interface.


Camera Calibration / Square Pixels and Center Principal Point
« on: June 21, 2011, 07:56:48 PM »
In the Calibration dialogue, there is an option to set Square Pixels. The word square is not presently found in the PDF version of the manual for Agisoft Lens. In the manual, under the section on calibration parameters there is a discussion of fixed aspect ratio. Does this option relate to the square pixels option? Likewise, the manual discusses "Fix Principal Point" while the options dialogue box reports Center Principal Point. Should I assume that these are likewise related?

Thanks in advance for any clarification that can be offered.


General / What are Model Generating P1 and P2?
« on: July 25, 2010, 07:20:21 PM »
In the preferences, on the advanced panel, there are parameters for P1 and P2. What are these and what aspects of processing do their values control? How should users think about changing these values to improve processing? I checked through the manual and online documentation and did not see any mention of these parameters. Any guidance on the informed use of these parameters would be appreciated.


General / Can't Build Model
« on: July 25, 2010, 06:58:58 PM »
Very often I add a group of images to a project, orient the cameras, and proceed to generate the model. The model generation process begins but fails and provides the error, "Can't Build Model". I have had this happen with even small groups of images (4) that are of the original camera resolution (8 megapixel). I have also experienced this problem with larger groups of images (20-25) that are downsampled to 4 megapixels.

Recently, the application seems to be crashing more frequently and rarely generating models. Can you provide any suggestions for how to increase the stability of the application and improve chances of generating models after camera orientation? In the mean time, on the chance that the instillation is now corrupt, I will be reinstalling the program. If this solves the problem, I will report back.

Thanks for any help you can provide. This is a wonderful program, and I'm looking forward to learning how to use it as efficiently as possible.

General / Downsampled Images
« on: July 25, 2010, 06:45:08 PM »
I see that the manual states that one should, "se the original files from your camera whenever possible". Is it acceptable to downsample images? When working with Photosynth or Bundler, I regularly downsample images to 2 or 4 megapixels respectively. On my computer, SIFT does not process images larger than 4 megapixels. I see that PhotoScan will align the 8 megapixel images that are produced by my Canon S90 camera. I found that PhotoScan will in some cases also process images that are downsampled by the ImageMagik command "mogrify -resize". However, in other cases downsampled images do not appear to solve well. Is there a preferred method of downsampling, or is there a preferred ratio--say 50%.

I suspect that downsampling images permits the processing of larger collections. At a full 8 megapixel size, there is more information in the photos than is required. Downsampling, when it works, results in faster processing and models with acceptable levels of detail. I would be very interested to learn if there are any suggested "best practices" when it comes to software used and downsampling factor applied. Any help would be appreciated.


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 / 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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