Version 3 (modified by emca, 8 years ago) (diff)

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Leica RCD digital camera

The system has a 39 megapixel digital camera, referred to as the "RCD" or "CH39", with the following characteristics:

  • 7216x5412 resolution, 12 bit [=~57MB raw]
  • 60mm lenses (changeable), with 44.2 degree x 34.0 degree FOV
    • fixed aperture (f-4.0)
  • pixel size 6.8microns (= ~15cm ground resolution at 1350m)
  • up to 1/4000 exposure time
  • Max frame rate 0.5Hz (2.02s per frame)
  • serial number 21
  • shutter is a dual curtain, one opening to start the exposure and the other closing to finish it
    • exposure will therefore occur at different times along the focal plane
    • 8ms for shutter to open and close, so there's a 4ms time difference between the top and bottom of the CCD acquiring light
  • lens distortion is a maximum of 2% at the edges of the FOV
    • distortion measurements are available
  • CCD is a Bayer array (raw 7162 x 5389), with a pixel layout as below. In the final processed TIFF, these pixels are blended and interpolated to make a full RGB grid.
Blue Green
Green Red

Logfiles contain various handy info, notably the image event file contains GPS time, (real time) pos/att and picture id

Calibration files are required and supplied by Leica (dark, gain and camera parameters).

File name convention is: DDHHMMSSXXXXXXGN.raw

  • DD = day of month
  • HHMMSS = timestamp
  • XXXXXX = incrementing picture id
  • G = gain (1-4)

Basic Image Processing

The RCD outputs raw images which are processed to create TIFFs. There are several image processing steps that are applied to each raw image.

  • Bias Correction
    The XXXd.tif file is used to subtract for ‘dark’ signals. “XXX” is the name of the camera parameters file.
  • System Response Correction
    The XXXg.tif file is used to correct for Pixel Response Non-Uniformity (PRNU) and for a first order system falloff in light across the image frame. “XXX” is the name of the camera parameter file.
  • Color Processing
    The XXXp.txt camera parameter file contains information on the camera regarding the Bayer array, color response, white balancing, and flaws. It is used to correctly interpolate from a Bayer image to full color RGB TIFF image, correct for color, white balance, and interpolate over flaws.

Orthophotos

This apparently takes another week long training course. We do have the basic software to do it but limited knowledge. Basic process is to determine the camera parameters, correct and overlay the images, keeping ideally only the most central parts. You then have to manually check through, especially along seams, and manually move the seam line in some instances (e.g. when perspective effects result in odd errors due to the seam hitting a tall building).

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