[wptabs style=”wpui-alma” mode=”vertical”] [wptabtitle] A BASIC INTRODUCTION [/wptabtitle]

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Why is pre-processing necessary?

For most close-range photogrammetry projects digital images will need to be captured in a RAW format, preserving the maximum pixel information which is important for archival purposes. Therefore it will likely be necessary to do some pre-processing in order to convert RAW images into a file format accepted by the photogrammetry software being used for the project.

If a color chart or gray card was using during image capture, it may also be useful to perform a white balance on the image set. There are a number of tools/software packages available for this purpose, but below we will describe a potential workflow using Adobe products for batch processing.

Overall steps of this workflow:

–  Batch convert RAW to DNG (Adobe DNG Converter)
–  Batch white balance (Camera Raw)
–  Batch image adjustments (Camera Raw)
–  Batch save to JPEG (or TIFF) format (Camera Raw)

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[wptabtitle] BATCH CONVERT RAW DATA [/wptabtitle] [wptabcontent]

Batch RAW to DNG with Adobe Digital Negative (DNG) Converter Software

As an open extension of the TIFF/EP standard with support for EXIF, IPTC and XMP metadata, the Adobe DNG format is rapidly becoming accepted as a standards for storing raw image data (primarily from digital photography).

For more information about file formats for archival, see the Archaeological Data Service (ADS) Guides to Good Practice.

Steps to Batch Convert:

1. Download and install Adobe DNG Converter. As of the date this workflow was published, version 7.2 of Adobe DNG Converter is a free tool available for download on the Adobe website.

Adobe DNG Converter is a free tool available for download on the Adobe website.

2. This tool converts an entire folder (aka batch) of images at one time. Use the tool interface to select the appropriate input folder containing the RAW images.

3. If needed, use the interface to design a naming scheme to be used for the new file names.

4. Set preferences for compatibility (e.g. Camera Raw 5.4 and later) and JPEG Preview (e.g. medium size). As an option, you can embed the original RAW file inside the new DNG files. This will, or course, increase the file size of the new DNG file.

5. Click “Convert” to start the process. Wait for this to finish.

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[wptabtitle] BATCH WHITE BALANCE – 1 [/wptabtitle] [wptabcontent]

Batch white balance, image processing, and exporting with Adobe – Part 1: Adobe Bridge

It is considered best practice to (correctly) use a quality color chart or gray card when capturing digital images for any CRP project.  Performing a white balance for each image set (or each lighting condition) can dramatically enhance the appearance of a final product (i.e. ortho-mosaic). This particular workflow uses Adobe Bridge and the Adobe Camera Raw tool, but a similar process can be done in other (free) software as well.

Adobe Bridge – Open in Camera Raw

1. Open Adobe Bridge and navigate to the folder containing the digital images (DNG files).

2. Select the appropriate images (including images with color chart/gray card).

3. Use the “File” menu to select “Open in Camera Raw”

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[wptabtitle] BATCH WHITE BALANCE – 2 [/wptabtitle] [wptabcontent]

Batch white balance, image processing, and exporting with Adobe – Part 2 : Camera Raw tool

4. Camera Raw will open and all of the selected images will appear on the left side of the window. Select the image with the color chart/gray card you would like to use for white balancing and other adjustments. Do all adjustments to this one image. We will apply the same changes to all images in the following slide ‘Batch Image Adjustment’.

Adobe Camera Raw – Image Processing Settings

5. By default, Camera Raw may attempt to apply a number of image processing settings that you should remove. This can be done using the interface on the right hand side of the screen. Check that all settings (with the exception of Temperature and Tint, which are set by the white balance tool in the next step) are set to zero. Be sure to check under each of the tabs.

6. Select the “Color Sampler Tool”  found in tool bar at the top of the window and:

A. If using a color chart, add a color sample inside the black and white squares. After adding these you should see the RGB pixel values for each sample.

B. If using a gray card, add a color sample inside the gray portion of the card.

7. Select the “White Balance Tool” from the tool bar at the top of the window and click on the gray portion of the chart (or card) to apply a white balance. At the same time, notice how the RGB values of the color sample(s) change. The RGB values should not differ by more than five or six (e.g. the white sample could be R: 50, G: 50, B: 51). If they differ by too much there could be a problem with the white balance. Try clicking a slightly different spot in the gray portion of the chart.

8. If other adjustments need to be made (i.e. exposure, brightness, contrast) make them now.

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[wptabtitle] BATCH IMAGE ADJUSTMENTS [/wptabtitle] [wptabcontent]

Applying adjustments to all

Once the white balance and adjustments have been made to this one image, we can apply the same to all the other images open in Camera Raw.

To do this, click “Select All” in the top left corner of the window – then click “Synchronize.” Wait for this to finish.

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[wptabtitle] BATCH SAVE TO JPEG OR TIFF [/wptabtitle] [wptabcontent]

Saving

Once the Synchronization is complete, click the “Save Images” in the bottom left corner of the window (make sure all images are still selected). The “Save Options” dialog allows you to choose a folder for the images to be saved to, a naming scheme, a file extension and format, and a quality/compression. Choose the settings you prefer and click “Save.”

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[wptabtitle] CONTINUE TO… [/wptabtitle] [wptabcontent]

Continue to PhotoScan – Basic Processing for Photogrammetry

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Working with the University of Arkansas’ Facilities Management and Planning Departments, CAST is documenting the historical Vol Walker Building and its renovation.  Here are merged scans of the second floor of the interior, which were collected with the Z+F 5005i Scanner.  The project includes multiple floors within the building interior as well as the building exterior.  Interior scans were collected with a point spacing that ranged from less than a centimeter at the most dense (at a range of < 1 meter) to approximately 5 cm at the least dense (at a range of 25 meters).  These scans were then reduced to a more consistent point spacing of 1 cm for potential future use in historical preservation documentation.  Exterior scans were collected with a point spacing of approximately 5-10 cm.  The data sets have been separated due to file size and data density.

Vol_Walker_Building_Interior_Floor_2 .zip (2.81 gb) (1 cm spacing in .pts file format)

Sitemap_Vol_Walker_Floor_2.htm -Explore the data set in Leica TruView, which requires Leica TruView free viewer and Internet Explorer.  For instructions on using the free TruView data viewer and for a complete list of links to the TruView data related to this project, please see: Accessing Vol Walker Interior TruViews.

Please note. This data is distributed under a Creative Commons 3.0 License  (seehttp://creativecommons.org/licenses/by-nc/3.0/ for the full license). You are free to share and remix these data under the condition that you include attribution as provided here.  You may not use the data or products in a commercial purpose without additional approvals. Please attach the following credit to all data and products developed there from:

Credits:

Data was collected in collaboration with University of Arkansas Facilities Management, Operations and Maintenance and Campus Planning Divisions with outstanding assistance from Bob Harris, Construction Coordinator.

Working with the University of Arkansas’ Facilities Management and Planning Departments, CAST is documenting the historical Vol Walker Building and its renovation.  Here are merged scans of the first floor of the interior, which were collected with the Z+F 5005i Scanner.  The project includes multiple floors within the building interior as well as the building exterior.  Interior scans were collected with a point spacing that ranged from less than a centimeter at the most dense (at a range of < 1 meter) to approximately 5 cm at the least dense (at a range of 25 meters).  These scans were then reduced to a more consistent point spacing of 1 cm for potential future use in historical preservation documentation.  Exterior scans were collected with a point spacing of approximately 5-10 cm.  The data sets have been separated due to file size and data density.

Vol_Walker_Building_Interior_Floor_1 .zip (2 gb) (1 cm spacing in .pts file format)

Sitemap_Vol_Walker_Floor_1.htm -Explore the data set in Leica TruView, which requires Leica TruView free viewer and Internet Explorer.  For instructions on using the free TruView data viewer and for a complete list of links to the TruView data related to this project, please see: Accessing Vol Walker Interior TruViews.

Please note. This data is distributed under a Creative Commons 3.0 License  (seehttp://creativecommons.org/licenses/by-nc/3.0/ for the full license). You are free to share and remix these data under the condition that you include attribution as provided here.  You may not use the data or products in a commercial purpose without additional approvals. Please attach the following credit to all data and products developed there from:

Credits:

Data was collected in collaboration with University of Arkansas Facilities Management, Operations and Maintenance and Campus Planning Divisions with outstanding assistance from Bob Harris, Construction Coordinator.

[wptabs mode=”vertical”] [wptabtitle] Project Planning[/wptabtitle] [wptabcontent]

Project planning includes a number of important considerations that will influence the success of the project. These include developing a strategy for the site/object, selecting the equipment and software to be used, calibrating equipment if needed, obtaining any required permissions, and starting the documentation process.[/wptabcontent]

[wptabtitle] Image and Control Acquisition[/wptabtitle] [wptabcontent]

There are a number of strategies for the collection of images in a photogrammetric project. Typically, the strategy is driven by the software used to process the images, and, more specifically, whether the type of processing requires a stereo or convergent (see figure below) set of images. This topic should be covered in the help file or manual for the software you plan to use.

Stereo (left) vs Convergent (right) image pairs

External control information can be added to a photogrammetric project for two reasons: 1) to position the model relative to a datum and/or 2) to provide geometric constraints on the photogrammetrically derived model. If the photogrammetric model is to be situated partially or wholly within an existing reference frame or datum (geodetic, mapping or local) then sufficient external references defined in this frame must be integrated into the project. A 3D reference frame or datum is defined by scale, position and orientation. Typically, reference information is in the form of control points (photo-identifiable points with known coordinates in a reference frame), lengths of photo-identifiable objects, and/or angles between photo-identifiable objects.

Adding Control Points in PhotoScan Pro

The minimum amount of information needed to scale, position and orient a photogrammetric model is two 3D control points and one 1D control point. If more than minimal control is provided (e.g. three or more 3D control points) then the control information could be used to help define the shape of the photogrammetric model as well as define its datum. In this case, the surveyor must ensure that the control information is, as a rule-of-thumb, at least 3x more accurate than the photogrammetric model itself. If it is not, then the control information will distort the photogrammetric model and potentially have deleterious effects on its relative accuracy.

It is also possible to apply control after a 3D model (mesh or other 3D CAD) has been created. In this case the control will only serve to position the model in space and will not cause distortion.[/wptabcontent]

[wptabtitle] Image Processing and Block Triangulation[/wptabtitle] [wptabcontent]

Most digital images captured in the field will require some digital processing, which include white balancing or any adjustments to the brightness, contrast, or other common image properties. One important note is to never crop (or change the height/width in any way) an image intended for photogrammetry.

In order to extract three dimensional points from two dimensional images, it is necessary to perform a triangulation with at least two images (a stereo pair). When more than two images are used in a triangulation, we refer to the group of images as a ‘block’. In order to perform a triangulation of the entire block (known as a bundle block adjustment), the user must measure a sufficient number of tie, control, and/or check points throughout the block. Constraints may also be placed on certain sets of points to enforce angular, linear, and/or planar properties. After a successful bundle adjustment, the user can extract and export 2D and/or 3D products.
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[wptabtitle] Creating and Exporting Deliverables[/wptabtitle] [wptabcontent]

Typical deliverables created as the end result of a CRP project could include 2D vector graphics (planimetric or elevation type CAD drawings), dense point clouds, 3D polylines, facetized models (mesh) of an object or surface, and raster graphics such as rectified or fully orthorectified images. Each deliverable created should include appropriate metadata for each of the above mentioned steps, as well as metadata for the additional processing performed to create the final file.[/wptabcontent]

[wptabtitle] Workflow Chart[/wptabtitle] [wptabcontent]This workflow provides a graphic overview of the steps involved in a Close-Range Photogrammetry Project. Click the image to see a larger version.

Basic Workflow of CRP Project