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Appropriate data sources

The ortho mapping workflow for historical aerial imagery is intended to photogrammetrically correct imagery that meets the following requirements:

  • Captured using panchromatic, natural color, or color infrared film
  • Stored as film negatives on rolls, film negative single frames, diapositives (roll or frame), or paper prints
  • Captured at nadir
  • Captured with a high quality mapping camera and lens, with fiducials visible, ideally with an available camera calibration report

The original film images need to be scanned before implementing the ortho mapping workflow.

If film has not yet been scanned, see preprocessing historical images for guidance.

Recommendations for existing digital files

If the film has already been scanned and you have digital files, you’ll want to consider the following.

Confirm that the fiducials are visible

Confirm that the fiducials are visible in the scans. If you have image files that have been edited so that the fiducials are not visible in the scans, it is strongly recommended that you redo the scans. The fiducials enable the system to accurately determine the camera coordinate system and improve the accuracy.

If you cannot get properly scanned image files, you can proceed with the ortho mapping workflow, but the image positions (even after block adjustment) may not be accurate.

Confirm the file format

Confirm that the image files are TIFF, JPG, JP2, or SID format. Any of these should work properly in the ortho mapping workflow, though JP2 format can be slow to read.

If you have a large number of files or notice performance problems, you may want to consider reformatting to TIFF files with internal JPG compression. (One option for converting or reformatting your files is OptimizeRasters.)

Determine the flight direction relative to the image orientation from the scanner

Review the files to determine flight direction. It is typical for film to be oriented in the digital scanner such that the direction of flight proceeds in +X direction of the image files (from left to right in the image file when an image is opened in a simple image viewer).

With a current version of ArcGIS Pro, the software will automatically compensate for incorrect scan orientation. However, if you have an older version of ArcGIS Pro, you can correct the scan orientation manually. The easiest method to verify the orientation of the scan relative to flight direction is to open two sequential photos from the same flightline in an image viewer and determine how to position the later photo relative to the earlier. (Make certain you don't pick images from the ends of two different flight lines). The standard orientation for scanning is for the later photo to overlap on the right (+X direction) relative to the previous photo. If your scan direction agrees with this description, the orientation is correct. If your later image must be positioned left, above, or below the earlier image, you can use the FCS field (see Exterior orientation) within the Frames table to adjust the rotation.

Once you've completed this review of your scanned images, you can proceed with the ortho mapping workflow.