Direct Georeferencing QA/QC Block Procedures for Aerial Camera, Part 2: Block Setup | GeoErnest

Direct Georeferencing QA/QC Block Procedures for Aerial Camera, Part 2: Block Setup | GeoErnest

To ensure that the final horizontal RMS ground accuracy is at the GSD level, a simple “QA/QC block” should be flown during each mission. This allows the geometric information of the image block to be combined with the independent information in the EO measurements (provided by your direct georeferencing system) in order to automatically check the quality of the system calibration and to verify the accuracy on the ground. You are basically completing a simplified boresight calibration.

Here are SEVEN characteristics to setup a QA/QC Block.

1. The QA/QC Block is ideally composed of a block of images with a minimum of 3 strips, with opposing flight direction, and 8 images in each strip

Remember, a QA/QC Block can be flown at any time during the mission

• For Block missions, a smaller QA/QC block can be simply subtracted from the full block,

• For Corridor and Single Photo Missions, 3 additional flight lines of 8 photos can be simply added to one of the existing strips at very little effort and cost

2. You must have your existing Airborne Geometric Calibration Report prior to any flight mission. These are your most recent boresight calibration report in conjunction with your latest camera calibration report

3. In the block, the image overlap should be 60% forward (minimum) and 20% sideward (minimum)

4. Make sure the QA/QC block has many features, ideally urban area because the QAQC procedures will create tie / pass points. You don’t what farm fields or golf courses

5. A few (2-3 minimum) Ground Control Points (GCP) are recommended in the QA/QC Block to

• Resolve any datum shift or GPS base station coordinate issues

• Detect any lever arm error

6. GCP accuracy is required to be within 5 cm horizontally and 5 cm vertically

7. GCP points are suggested to be Differential GPS surveyed using the same GPS Base Station location and coordinates as the Airborne Calibration Flight. This minimizes datum transformation errors.

You should have airborne geometric calibration software. Run this with your QAQC block data. You will create Refined Calibration Parameters that are mission specific values. You have re-calibrated you Xp/Yp, boresight values and local datum shift. If the changes are significant, apply the results to the current project flight only.

If your results improve your accuracy, it is very likely that something in your sensor system shifted. You should strongly consider performing a complete airborne geometric boresight calibration.

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