Quality Control Review of Orthophotography

1
Quality Control Review of Orthophotography

• Matt McCormack, I.M.A.G.I.S.

2
Goals to talk about today

• Definitions
• How the Orthophotography Project deliverables and
  specifications influence review
• The hows and whats of reviewing the ortho and
  other related deliverables
• Examples, last thoughts, and finally
• Questions and (hopefully) answers section

3
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.

4
Single Frame Ortho
5
Multiple Rectified Frames
6
Mosaic Processing
7
Marion County Final Mosaic
8
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.

9
Ortho .5 foot resolution
10
Ortho 2.0 foot resolution
11
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.

12
Dodging Film
13
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.

14
Digital Camera Example
15
Color Balance
Before
After
16
Another Example
17
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.

18
Ghost Image
19
Orthophotography Project deliverables and
specifications

• Revisit and know your project deliverable
  specifications! You cant expect a vendor to
  fix what he didnt 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.

20
Surface Error I
21
Surface Error II
22
Outdated Surface Errors
23
DEM makes photo swim from year to year as
seen in road edge.
24
Orthophotography Project deliverables and
specifications (cont.)

• Know your specs (cont.) Other products- CIR,
  Surface Data, Subsets Medium- External Hard
  Drive (recommend), DVDs 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

25
Traditional Ortho 07
26
True Ortho 05
27
Traditional vs. True Orthos
28
Orthophotography Project deliverables and
specifications (cont.)

• Know your specs (cont.) Is Vendor required to
  fix bridges/features What are you willing to
  accept vs. impact to organization (foliage,
  water, shadows, dates)

29
Requirements? Not in 93!
30
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.

31
Review Prep and Steps

• Plan for huge amount of data! DEMS, CIR, Tiffs
  need LOTS of room
• Select Review Software Familiarity and ease of
  use!
• Plan for Staff Time Delivery Schedules always
  change! Train so everyone on same page
• Develop and Follow Procedure Document,
  especially for multiple Staff

32
Review Prep and Steps (cont.)

• Image Review Documentation Date Initials Commen
  ts (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 questions Do this in
  a timely manner so they can act on them, it
  might save them time to head-off the issues
  early.

33
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.

34
Review Prep and Steps (cont.)

• Review re-submitted files Check identified
  errors for resolution Give the entire file a
  once over for an new issues that might have
  occurred.

35
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!

36
What to look for during the review (cont.)

• Overview or First Review Load 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 isnt missing any
  data, look for obvious color balance and
  contrast/brightness issues.

37
Review Example 1
38
Wrong World File
39
What to look for during the review (cont.)

• 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 isnt missing any
  data, look for obvious color balance and
  contrast/brightness issues.

40
Review Example 2
41
Missing Data at Tile Edge
42
What to look for during the review (cont.)

• Detail View- view at final scale or higher View
  at final mapping scale (ie, 1100/11200) 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.

43
Review Example 3
44
Review Example 4
45
What to look for during the review (cont.)

• Detail View- Shortcuts In 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.

46
Source Reference Data
47
What to look for during the review-Common
Features and Problem Areas

• Warped bridges, overpasses, and above ground
  features Surface 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.

48
Overpass Distortion
49
Linear Feature Issue
50
Pavement warped at overpass
51
What to look for during the review-Common
Features and Problem Areas

• Buildings/Large Structures Buildings and large
  above ground features that have imagery from
  more than one image will look like they have
  collapsed, a common seaming error in a mosaic.
• Excessive building lean or warping Urban or
  downtown areas often have additional images to
  minimize the leaning caused by displacement,
  and large buildings sometimes appear wavy or
  warped during rectification.

52
Seam and Collapsed Feature
53
Visual Clue?
54
Seam or Feather Issue
55
Seam Line Error
56
Seam Line Error II
57
Image Smear at Bridge
58
Distorted Building
59
What to look for during the review-Common
Features and Problem Areas (cont.)

• Excessive or long shadows Should be flown at a
  time of day that minimizes this problem,
  exacerbated by contrast/brightness issues.
• Ground/Atmospheric Conditions Snow cover,
  Foliage, Flooding, Clouds or Haze are all issues
  that should meet specifications.
• Seams/Feathering Cutting through building, fuzzy
  along features, mismatching

60
Shadows, Building Lean
61
What else to look for during the review

• Ground Accuracy Measure Targets/Control Compare
  to planimetrics or previous Orthos Beware old
  source my be LESS accurate Find other Source
  Data for comparison Survey field checks Measure
  pre-selected blind control points

62
Target or Panel
63
(No Transcript)
64
Use other sources when available
65
Using Pictometry to show distortion in Ortho
66
Guitar Pool
67
Last Thoughts

• Consider Contracting with a qualified Vendor if
  you have the resources

68
Questions????
69
Thanks for listening, and have a great day!