Topic 12 Flashcards
(22 cards)
vector clip
overlay clip feature on input layer
determine locations where polygon boundaries are coincident, identify the line segments that intersect
raster clip
determine range of pixel rows and columns for the clip region
eliminate pixels that fall outside the clip extent
local operations
on raster data refer to cell-by-cell operations
can be performed on a single or multiple raster images
summary statistics (mean, min, max)
what operations are useful for activities such as change detection analysis
local operations
map algebra
mean map, local operators
depdends on what you want to accomplish
detect historical landscape changes
outcome of boolean expression is binary
map algebra definition
process of constructing siple numeric models based on overlaying raster layers and performing mathematical operations on the layers
extended map algebra
becomes much more complicated with more raster sets
neighbourhood (window) operatios
in Arcgis (statistical or convolution)
works on a neighbourhood of cells, then moves the window to a new set of cells
typically done on a single raster
can be high or low frequency
spatial filtering (phones)
low pass filters
removes the high frequency information (noise) and shows general trends in the data
smoothing operation
high pass filter
removes the low frequency information and show the high frequency (sharpening)
neighbourhood operation
widely applied in a variety of raster applications
remote sensing texture analysis
DEM processing
spatial filtering
focal cell
local or pixel of interest (spatial interest)
the windows do not have to be square
block or focal neighbourhoods
masks and windows
windows are positioned over a focal pixel
spatial filtering (convolution)
operations are performed using a moving window and a spatial neighborhood within a single raster layer
convolution coefficients
the moving window (kernel) is a matrix of convolution coefficients (weights)
mean low pass filter raster values
1/9
laplacian (edge detector values)
-1
adds up to 0
laplacian filter
high-pass filter
extract, enhance, add back into the original image
adds edge to high frequency info
edge detector
usually for aesthetics
zonal operations
zonal statistics
refers to raster analysis restricted to regions or zones within the map
window size and shape not regular (polygons)
MAUP
MAUP
the influence of modifiable areal units on statistical analysis
shifting boundaries, shifting results
two problems of MAUP
1) measurement scale
2) aggregation
solutions to MAUP
define fundamental entities
avoid using arbitraily define scales’’
use spatial statistics where able
