Topic 6: OBIA Flashcards
OBIA stand for
Object based image analysis
what does OBIA do
divides remote sensing imagery into meaningful image objects and assigning characteristics
what is Scale in remote sensing
Grain
- spatial resolution
Extent
- swath width
this is a trade off
what is the optimal scale
there is no single optimal scale for defining geographic entities
why is scale an issue
results and conclusions may only be a result of one specific scale
MAUP stands for
Modifiable areal unit problem
what is MAUP
is the sensitivity of analytical results to the definition of data collection units.
what are the two components of the MAUP
- scale problem
- aggregation problem
what is the Scale problem in the MAUP
variation in results when areal units are aggregated into fewer and larger units for analysis.
eg. resampling to larger pixel sizes
what is the aggregation problem in the MAUP
variation in results generated bu alternate zoning schemes at the same resolution.
Whats the relationship between between variance and correlation coefficients
lower variance (smoothing) results in stronger correlation
what are solutions to MAUP
- Abandon traditional statistics
- conduct a sensitivity analysis
- derive an optimal spatial resolution
- identify basic entities or objects
what is an optimal spatial resolution
no simple solution, application dependent
what is spectral classification
spectral classes are converted into information classes.
what are the three types of classifications
- supervised
- unsupervised
- hybrid
what is Pixel mixing
one one pixel represents multiple classes with no one clear signal
- composite signatures
what are competing effects of increased spatial resolution?
- less pixel mixing with high spatial resolution
- greater within-class variability.
summarize the MAUP problem
whenever a grid is assigned to a physical area there is inherent error in the way the data is aggregated.
OBIA as a solution for MAUP
provides soltion as features are not only pixel values based
what are objects
are basic entities within an image that are composed of h-res pixel groups
- we use shape, texture, colour and context to define shapes
intigration of Image objects to GIS
pixels: raster data model
objects: vector data model
OBIA provide what aspects for analysis
Spectral Variables
Shape variables
Texture Variables
Context
what are spectral variables
feautres related to the value of pixels within an object
what are Shape variables
Features to the shape of an image object, length, width, direction, area
texture variables
features related to spatial patterns of pixels within an object
what is Context in a OBIA
Features related to the spatial setting of an object within scene and/or its relationship to other objects in the scene
what does one-to-one correspondance in OBIA mean
the geographic entity is perfectly selected and the correct spatial scale is being used.
what is segmentation
pulling discrete regions out of an image
how is a segmentation preformed
- using premade algorithms
- expert knowledge of your image and application
- calibrate, trial and error
what are the two types of segmentation algorthims
1 discontinuity based
2 similarity based
what is a discontinuity based algorithm
image i sbroken based on abrubt changes in intensity, edge detection
what is similarity based algorithm
image is broken using regions based on pre-defined criteria using spectral or spatial information
Laplacian edge detection
-discontinuity based Segmentation algo
-directionally invariant edge detection
Sobel edge detection
another algo for dicontinuity based segmentation
thresholding
similarity based segmentation.
partioning a histogram
region based segmentation
similarity based segmentaion that partitions an image based on region growing approach
- seed points
- growing regions
what is Trimble
a segmentation algorithm that is a region merging technique
- process can be repeated at many scales
OBIA workflow
depends on purpose
partitioning an image into meaningful image objects requires….
an effective segmentation technique
melt ponds
ponds that form on the top of glaciers that increase melting
is C-band frequency SAR Capable of providing a seasonal prediction of spring melt ponds?
