requiring a spatial reference the: need for rectification
DESCRIPTION
REQUIRING A SPATIAL REFERENCE THE: NEED FOR RECTIFICATION. Why Rectify?. Recall . . . -all attribute data in a GIS must possess a spatial reference - PowerPoint PPT PresentationTRANSCRIPT
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REQUIRING A SPATIAL REFERENCE THE:
NEED FOR RECTIFICATION
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Why Rectify?
Recall . . .
-all attribute data in a GIS must possess a spatial reference
-ideally, data from all sources intended for use in the same GIS would share identical datum, projection, ellipsoid, and coordinate properties
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Why Rectify?
What reference is right?
-many datasets have “shifts,” some which are known and documented and some which are not known
-metadata is important, from data acquisition, to data handling, and ultimately to data delivery or database management
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Standard Rectification
Many forms (algorithms):
-the most common is polynomial rectification
-based on the principles of regression
-raw data is forced to fit a reference
-can be completed in 2-dimensions (X,Y) or 3-dimensions (X,Y,Z)
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Standard Rectification
Choosing the appropriate reference data:
-data must be at a comparable (suitable) scale
-if possible, the phenomena represented by the data should have no spatial-
temporal relationship (i.e., the features should not move over time)
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Standard Rectification
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Standard Rectification
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Standard Rectification
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Standard Rectification
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Standard Rectification
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Standard Rectification
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Standard RectificationAdding more information . . .
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Orthorectification
• Orthorectification :
When an image or photo has been put into an orthogonal plane to Earth by removing camera orientation errors, satellite errors, terrain & relief, etc.
Rectification or Geometric Correction :
Photos or images have been corrected for incidence error in capturing the data as well geometric error caused by earth rotation
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Need for a DEM
Digital Elevation Model:
- Continuous raster layer in which data file values represent elevation (z-value)
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Ortho – Process Overview• Planning and Scanning Photos
• Gathering reference information such as lakes, contours, roads, streams, (vectors).
•Interpolate DEM (Digital Elevation Model).
• Enter Camera Calibration report
• Complete Interior points entry
•Select GCP’s / or enter known GPS points
•Creating automatic Tie points
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Ortho Process Cont’d
* Model convergence
* Examination and Evaluation of the triangulation process.
* Color Balancing
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Getting Started…..
Scanning Photos…..• Time consuming
• Important to know the meta data
• Organization is key
• Back up as you go, not when you are finished…….
• Capture all of the fiducial points and make notes of unusual photos or photo orders.
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Digital Elevation Model
DEM• There are several ways to create a
surface…….. be critical of your product
• Some software has problems with contour and elevation data
• Interpolation of contours ……non or linear?
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Digital Elevation Model
Interpolation ??
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Camera Calibration Report
• Date of calibration
• Focal rating
• Assessment of lense distortion (fiducial distortion)
• Angular distortion
• Locations and distances between fiducial points
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Interior Control
• Bring photos online
• Building pyramid layers
• Interior control corrects the model to the camera calibration information
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Camera Report / Interior Control
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Control Points
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Automatic Tie Point Generation
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Triangulation
• Is the mathematical relationship between the photos, the ground and the camera
• Traditionally completed using stereo plotters allowing the user to capture ground control points using the control point extension techniques
• Digital Triangulation extends the traditional methods to offer: determining image position, determine tie point ground relationships with the overlap, dispersal of error over the block
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Block Bundle
• Views all of the photo as one image
• Allows different types of data to be incorporated into the mosaic
• This allows the software to statistically Identify error
Distribute error
Remove error
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What is a Block Bundle???.....
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Error Checking
• Time Robust Error checking
• Advanced Robust Error checking
• Final error checking (Model is accepted and the points are then moved…..)
• ECW compressed trial mosaic product with lakes, and roads coverages.
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Completed Mosaic ??
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Color Balancing…..
Before Almost After ….
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Color Balancing
• Masking over exposed areas (CIR)
• Buffering lakes and Region growing (Both)
• Lakes are essentially lifted out
• Final color balancing tweak is completed.
• Software--- ER Mapper, Erdas Image Equalizer
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Managing Error
• Scanning • Different Photo dates• Processing Time• Error assessment• Color balancing• Large files = large hard drives• Projections• Tree shadows, or at the other end of the spectrum lake
reflection or significant portions of bedrock• Large lakes
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The Lakes Problem….
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Benefits of an Ortho Mosaic
• 1 metre resolution data (color)
• Data has been corrected to represent the land base
• Excellent Map backdrops when compared to standard line topo - maps
• Verification of cut block layout
• New GPS units have the capabilities to handling compressed photo back drops.
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Benefits of Ortho Mosaics
• Each pixel posses geometric properties
• Measurements taken from a properly prepared orthorectified product represent the corresponding measurements that would be taken in the field
• Updates or additional photos can easily be added to the bundle block model
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Where are we Going....??
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Improving Ground Work
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Multi- scale Concurrent Inventories
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GIS Database Development