Nikon D200 IR Calibration

Below are camera calibration values for the CAST Nikon D200 IR camera with Nikkor 28 mm lens. For projects requiring highest accuracy it is recommended that you perform your own calibration, otherwise these values can be used.

PhotoModeler v2012 Calibration Values (August 2013, F-stop of f/8, overall RMS 0.218 pixels):
– Focal Length: 29.630373 mm
– Xp: 11.836279 mm
– Yp: 8.051145 mm
– Fw: 23.999451 mm
– Fh: 16.066116 mm
– K1: 1.435e-004
– K2: -1.481e-007
– P1: 5.659e-006
– P2: -1.311e-005

Calibration Values for PhotoScan (converted from PhotoModeler values using Agisoft Lens):
– fx: 4.7804273068544844e+003
– fy: 4.7803319847309840e+003
– cx: 1.9096258642704192e+003
– cy: 1.2989255852147951e+003
– skew: -8.0217439143733470e-004
– k1: -1.2545715047710407e-001
– k2: 1.5266014429827224e-001
– k3: -7.6547741407995973e-002
– p1: 3.5948192692070413e-004
– p2: -1.5418228415832919e-004

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)

[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.
[/wptabcontent]
[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