Nikon D200 IR Light Transmission

Because of the light transmission properties of the filter installed in the CAST Nikon D200 IR DSLR camera, it is possible to isolate infrared and red light into separate channels. These channels can then be used to generate an NDVI image using the well known formula:

NDVI = (NIR – Red) / (NIR + Red)

We’re calling this pseudo-NDVI for a couple reasons; 1) the IR filter installed only captures a portion of the visible red (probably less than half), so this bit of information is relatively weak, and 2) our method of isolating the “reflected red” (Band1 – Band3) is overly simplistic. However, we have tried more complicated methods (e.g. principal components, also averaging bands 2 and 3) but results did not improve. Without more work, the results of this process should not be compared to calibrated NDVI images.

1. Load (individually) bands 1 and 3. Band 1 represents Red+IR, Band 3 is IR only.

Nikon D200 IR Bands 1 and 3

2. Run the Raster Calculator tool to produce a “reflected red” raster using the following raster math:
Band1 – Band3

Nikon D200IR “Reflected Red”

3. Run the Raster Calculator tool to produce NDVI raster using:
(Float(“Band3”) – Float(“ReflectedRed”)) / (Float(“Band3”) + Float(“Reflected Red”))

Nikon D200IR Quasi NDVI

Note: If you don’t use the Float functions in step 3 you end up with integers (-1,0,1), which are useless.

Nikon D70 and Nikkor lenses

Along with the generic advise given in the Acquire Images for Close-Range Photogrammetry and Custom White Balance for Nikon D200 IR posts, here are some important settings to consider when using the standard or IR modified Nikon D200 cameras:

– Rotate Tall: Set “Rotate Tall” to Off if the images are to be used for photogrammetry or GIS applications

– Image Quality: Use either the “NEF (RAW)” or “NEF (RAW)+JPEG” image quality setting. Capturing RAW images will preserve all image information and give you much more control over editing later

– Image Size: Set to “Large 3872×2592/10.0M”

– Optimize Image: Use these “Custom” settings and adjust as needed:

–Image Sharpening = None
–Tone Compensation = Normal (0)
–Color Mode = III
–Saturation = Normal (0)
–Hue Adjustment = 0
–Make sure you select “Done” after making adjustments to theses settings or they will be lost.

– Color Space: Should be set to “sRGB”

– JPEG Compression: For highest quality set to “Optimal Quality”

– RAW Compression: If memory card space is not an issue, set to “NEF (RAW)” for no compression. Otherwise turning on compression will cut the size of RAW images from 16MB to 9MB

– Intvl Timer Shooting: This setting can be used to take a predetermined number of images with a certain amount of time between each shot. To use this setting, three setting must be set:

1. Start: Two options exist including “Now” (starts taking images right away) or “Start Time” (allows you to set a time (e.g. 13:00, aka 1pm). If using Start Time, make sure the cameras time setting is correct
2. Interval: Sets the amount of time between each interval using hours, minutes, and/or seconds (one second minimum)
3. Select Intvl*Shots: This setting ask you to set 1. the total number of intervals and 2. number of images at each interval. If mounting the camera to the octocopter for example, one could set the Interval to 10 seconds, the total number of intervals to 50, and the number of images at each interval to two. This would result in 100 total images, with two at each of the 50 positions (interval)

Nikon D200IR Custom White Balance Results

Because some red light is transmitted by the IR filter, any of the standard white balance settings will produce reddish images. A custom white balance using the “White Balance Preset” option can be used for better images. It’s important to note that the white balance setting is only applied to JPEG images saved on the memory card – RAW images are saved to the memory card exactly as they are recorded by the image sensor, without any processing. However, even when capturing RAW images, the image preview on the camera’s LCD will use the white balance setting, and will therefore be easier to evaluate exposure in the field.

To use the White Balance Preset option, follow these instructions to capture an appropriate custom WB image:

1. Hold down the “WB” button and rotate the rear wheel to select the “PRE” setting, release WB
2. Hold down the “WB” button until “PRE” begins to flash
3. Use the shutter release button to capture a photograph of healthy green grass in similar lighting as your intended subject (e.g. direct sun)
4. The camera should indicate “Good” or “No Gd” – if “No Gd” try again
5. If the camera indicates Good, take a test image to visually check your white balance

“Good” close-range photogrammetry example from Ostia Antica, Italy. Note that the object (the temple) is framed tightly, and that all objects (both near and far) are in sharp focus.

When it comes to close-range photogrammetry, the difference between “good” photos and “bad” photos can be the difference between getting useful 3D information and having complete failure. There are many different variables contributing to success or failure of a project, but to help avoid the most common mistakes a photographer can follow the general guidelines outlined below.

Basic photographic concepts that, when followed, generally produce acceptable digital images:

Camera/lens Properties:
-Use a mid to high resolution camera (at least 12-15MP)
-Use a fixed (non-zoom) lens
-Tape the focus ring (and set to manual focus)
-If using a zoom lens, tape the zoom ring and use one focal length for the entire project

Camera Placement:
-Use a tripod and stable tripod head
-Frame the subject tightly, making use of the entire sensor area
-Maintain 60-80% overlap between photos
-Ensure all important areas of the object are visible in at least three images
-Be aware of camera geometry required by software (baseline, convergent angles)

Camera Settings:
-Use aperture priority mode (set to between f/8 and f/16)
-Use a timer or wired/wireless shutter release to minimizes motion blur
-Use mirror lock-up, if available, to further minimizes motion blur

A list of common mistakes made while capturing digital images for a close-range photogrammetry project:

Camera/lens:

“Bad” close-range photogrammetry example. Note that the object (the temple) is not framed tightly, and that most objects are blurry and out of focus.

-Use of low resolution camera (8MP or less)
-Changing zoom (focal length) between images
-Use of loose/damaged lens
-Significant re-focusing due to varying distance from object

Camera placement:
-Handheld camera (no tripod)
-Insufficient overlap between images
-Inefficient use of sensor area (too far from subject)
-weak camera geometry (multiple images from one position, short baseline, overall poor network of image locations/orientations)

Camera settings:
-shallow depth of field (below f/8)
-manual shutter release (causes motion blur)

[wptabs type=”tabs” effect=”none” mode=”vertical”] [wptabtitle] Learn more about depth of field, bit depth, EXIF metadata, file formats, and more…[/wptabtitle] [wptabcontent]
Glossary of terms found at Digital Photography Review website (dpreview.com)
http://www.dpreview.com/learn/?/Glossary/[/wptabcontent] [wptabtitle] ADS Guides to Good Practice[/wptabtitle] [wptabcontent]

Learn more about the ADS Guides to Good Practice for close-range photogrammetric documentation…
Barnes, A; J. Cothren, K. Niven (2011) Guides to Good Practice: Close-Range Photogrammetry. Archaeology Data Service / Digital Antiquity: Guides to Good Practice.
http://guides.archaeologydataservice.ac.uk/g2gp/Photogram_Toc[/wptabcontent]

[wptabtitle] Documenting Surfaces[/wptabtitle] [wptabcontent]An excellent guide for using close-range or aerial photogrammetry to document surfaces (e.g. rock art, trackways, surfaces prone to erosion).
Matthews, N. A. (2008) Aerial and Close Range Photogrammetric Technology: Providing Resource Documentation, Interpretation, and Preservation. Technical Note 428. National Operations Center, Denver, Colorado: U.S. Department of the Interior, Bureau of Land Management.
http://www.blm.gov/nstc/library/pdf/TN428.pdf[/wptabcontent]

[wptabtitle] HABS/HAER/HALS[/wptabtitle] [wptabcontent]Learn more about architectural and engineering documentation for long term archival in the Heritage Documentation Programs collections in the Library of Congress.
National Park Services: Heritage Documentation Programs (HABS/HAER/HALS)
http://www.nps.gov/history/hdp/[/wptabcontent]

[wptabtitle] Cultural Heritage Site Surveying[/wptabtitle] [wptabcontent]What makes a successful and useful survey of cultural heritage sites? Learn what to record, how to record it, and what performance indicators are important…
Bryan, P., B. Blake, J. Bedford, D. Barber, J. Mills, and D. Andrews (2009) Metric Survey Specifications for Cultural Heritage. English Heritage, Swindon.
http://www.english-heritage.org.uk/publications/metric-survey-specification/[/wptabcontent]

[wptabtitle] English Heritage on Photogrammetric Survey of Historic Buildings[/wptabtitle] [wptabcontent]An extensive and detailed guide for the photogrammetric survey of historic buildings…
D’Ayala, D., and P. Smars (2003) Minimum requirements for metric use of non-metric photographic documentation, University of Bath.
PART 1: http://www.english-heritage.org.uk/publications/metric-use-of-non-metric-photographic-documentation/metricextraction1.pdf/
PART 2: http://www.english-heritage.org.uk/content/publications/publicationsNew/metric-use-of-non-metric-photographic-documentation/metricextraction2.pdf[/wptabcontent]

[wptabtitle] Intro to Architectural Photogrammetry[/wptabtitle] [wptabcontent]A nice introduction to close-range photogrammetry and methods for architectural photogrammetry…
Hanke, K., and P. Grussenmeyer (2002) Architectural Photogrammetry: Basic Theory, Procedures, Tools. September 2002, ISPRS Commission 5 Tutorial, Corfu.
http://www.isprs.org/commission5/tutorial02/gruss/tut_gruss.pdf[/wptabcontent] [/wptabs]

Aligned Images in PhotoScan

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’. To perform a triangulation, we 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. Once a triangulation is successful, image exterior orientation parameters (along with estimate for accuracy) should be available to the user. These are important pieces of information for downstream deliverables and should be documented. The table below describes the appropriate documentation for this process. Download a printable form in PDF format here or in a spreadsheet (.xlsx) format here.

Camera Calibration Photo

Each camera (referring to a camera and lens combination) used in a close-range photogrammetry project should be calibrated and a calibration file should be saved with the project data. Some close-range photogrammetry software does not require this information before processing the image block; however, it will provide most of this information after processing. The tables below describe what is appropriate to document for this process. Download a printable form in PDF format here or in a spreadsheet (.xlsx) format here.

For each camera/lens calibration:

For each calibration image (if performing a camera calibration with a target):

Nikon D70

Organization and documentation during image collection in the field is especially important. The table below describes the appropriate documentation for this process. Download a printable form in PDF format here or in a spreadsheet (.xlsx) format here.

For each group of images: