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Quality Control Review of Orthophotography. Matt McCormack, I.M.A.G.I.S. Goals to talk about today. Definitions How the Orthophotography Project deliverables and specifications influence review The how’s and what’s of reviewing the ortho and other related deliverables
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Quality Control Review of Orthophotography Matt McCormack, I.M.A.G.I.S.
Goals to talk about today • Definitions • How the Orthophotography Project deliverables and specifications influence review • The how’s and what’s of reviewing the ortho and other related deliverables • Examples, last thoughts, and finally… • Questions and (hopefully) answers section
Definitions • Orthophotography- aerial photos that have been “rectified” or adjusted to form to the project terrain and geo-referenced to the clients specifications. Relief and camera, as well as certain “feature” distortions have been removed, and the “frames” or “lifts” have been stitched together to form a “seamless” mosaic of the project area.
Definitions (cont.) • Clarity- generally referring to the amount of detail an image will render. Closely related to the flight height, weather conditions, lens and camera quality, final pixel resolution, and ground conditions when the mission was completed. Processing may also affect clarity of the image.
Definitions (cont.) • Radiometry- bright areas and dark areas in an image, typically adjusted for in the image processing technique known as “dodging”, or limiting overexposure in the light areas of an image and doing the opposite in dark or shadowed areas.
Definitions (cont.) • Color Balance- Ultimately adjusting the RGB composition to achieve a true color representation of each image and the images in the mosaic. Digital cameras may over-emphasize one or more of the red, green, or blue hues making this a very important step.
Before Color Balance After
Definitions (cont.) • Ghosting- a visual anomaly in a image where there are “left over” artifacts from an image used during the mosaicing process. Distorted, vehicles, offset features, and blurred imagery can occur as a result of the type of camera used, feathering routine in the software, or inadequate surface data.
Orthophotography Project deliverables and specifications • Revisit and know your project deliverable specifications! You can’t expect a vendor to “fix” what he didn’t “break”. Flight/Camera- height, lens, digital vs. film. Pixel resolution- match flight, camera, needs (consider multiple resolutions where possible). Surface/DTM- existing, develop new, edit previous Tile/Grid- naming convention, tile graphic by delivery Format(s)- tiffs, sids, qc area sids, twp sids Delivery Schedule- increment deliveries.
DEM makes photo “swim” from year to year – as seen in road edge.
Orthophotography Project deliverables and specifications (cont.) • Know your specs (cont.)Other products- CIR, Surface Data, Subsets Medium- External Hard Drive (recommend), DVD’s Flight Logs- Frame/Lift graphic with date/time Pilot Area(s)- Highly recommend representative pilot areas! Flush out issues before production. Color Balance, contrast, and brightness preferences Ask to see samples of areas with similar specs/needs. Extra Flights Downtown/True Orthos
Orthophotography Project deliverables and specifications (cont.) • Know your specs (cont.)Is Vendorrequired to “fix” bridges/features What are you willing to accept vs. impact to organization (foliage, water, shadows, dates)
How to Approach the Review • A planned approach is usually the best, so the following slides are some things to anticipate when setting up a review process.
Review Prep and Steps • Plan for huge amount of data!DEMS, CIR, Tiffs need LOTS of room • Select Review SoftwareFamiliarity and ease of use! • Plan for Staff TimeDelivery Schedules always change! Train so everyone on same page • Develop and Follow Procedure Document, especially for multiple Staff
Review Prep and Steps (cont.) • Image Review DocumentationDate Initials Comments (standardize) Observation Location (x/y, tile, point or graphic) Screen Capture (ie, SnagIt) Graphic- Shape file with fields in .dbf, Spread Sheet • Submit review “issues” and questionsDo this in a timely manner so they can act on them, it might save them time to head-off the issues early.
Review Prep and Steps (cont.) • Submit review “issues” and questions (cont.) The sooner they get them resolve and back the sooner you can move on to the next step, may affect other products like county, township, or municipal mosaics.
Review Prep and Steps (cont.) • Review re-submitted filesCheck identified errors for resolution Give the entire file a once over for an new issues that might have occurred.
What to look for during the review • Now, you have all of these files to review, they are all loaded and accessible. Now you need to know where to look for unacceptable images with “issues” and how to communicate that back to the vendor. All the while everyone is asking the same question, “When can I get a copy of the aerials?”. No pressure there!
What to look for during the review (cont.) • Overview or First ReviewLoad all of the tiles with the corresponding grid and note any missing, corrupt, or outliers (wrong projection or wrong/missing geocoordinates). • Full View View each tile at full view to make sure it “ties” to adjacent tiles, is the right image for the world file, and isn’t missing any data, look for obvious color balance and contrast/brightness issues.
What to look for during the review (cont.) • Full ViewView each tile at full view to make sure it “ties” to adjacent tiles, is the right image for the world file, and isn’t missing any data, look for obvious color balance and contrast/brightness issues.
What to look for during the review (cont.) • Detail View- view at final scale or higherView at final mapping scale (ie, 1”=100/1:1200) or higher magnification to see detail and look for common errors or “issues”. Pan in a consistent pattern starting in one corner and across or down and “snake” through the tile. Increase magnification or use “window” to look more closely at features of interest. Note and document, then check-off reviewed tile before moving on to next.
What to look for during the review (cont.) • Detail View- ShortcutsIn rural areas, may want to only zoom in on features and areas where errors are more common, like bridges, building, roads, steams. This will increase your speed (and lessen the boredom). Reference data like a state or county bridge, road, or drainage mapping file can be a great time saver. More built- up areas require more time and diligence.
What to look for during the review-Common Features and Problem Areas • Warped bridges, overpasses, and above ground featuresSurface data does not always support the rectification of these features, so it is not uncommon to find these features distorted. • Distorted roads, railroads, linear features Long straight features should be review for distortions like offsets at seams, dips, holes or hills in the elevation can cause curved distortions along linear features.
