Presentation on theme: "REQUIRING A SPATIAL REFERENCE THE: NEED FOR RECTIFICATION."— Presentation transcript:
REQUIRING A SPATIAL REFERENCE THE: NEED FOR RECTIFICATION
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
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
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)
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)
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
Need for a DEM Digital Elevation Model: - Continuous raster layer in which data file values represent elevation (z-value)
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 GCPs / or enter known GPS points Creating automatic Tie points
Ortho Process Contd * Model convergence * Examination and Evaluation of the triangulation process. * Color Balancing
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.
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?
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
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
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.
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
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
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.
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