Inverse distance weighted interpolation¶
Introduction¶
Added in version 8.0.
The inverse distance weighted interpolation is a method to rasterize vector features with a weight that is the inverse of a power of the distance between the target pixel and the source feature.
Configuration¶
First, you must set the LAYER CONNECTIONTYPE parameter to IDW. The vector-to-raster interpolation takes the following parameters:
CONNECTION «layername» : reference to the NAME or GROUP of a LAYER to use as an input vector datasource. NAME takes precedence, followed by the first layer from GROUP who’s minscaledenom/maxscaledenom matches the current map scale. The referenced layer should be a TYPE POINT layer. Other layer types will result in one sample being added for each vertex of the input features.
PROCESSING «IDW_RADIUS=10» : Radius in pixels of the search radius of features to take into account. Higher values result in increased cpu time needed to compute the filtered data. The default is the dimension of the image to render.
PROCESSING «IDW_COMPUTE_BORDERS=ON|OFF» : A kernel of radius «r» cannot be applied to «r» pixels along the borders of the image. The default is to extend the search rectangle of the input datasource to include features «r» pixels outside of the current map extent so that the computed result extends to the full extent of the resulting image. This can be deactivated when tiling if the tiling software applies a metabuffer of «r» pixels to its requests, to avoid the performance overhead of computing this extra information.
PROCESSING «IDW_POWER=numeric» :
Value such that 1 / distance^power is the weight applied when computing pixel values. The default is 1.0.
Advanced sample weighting and filtering¶
See corresponding section of Kernel Density Estimation (Dynamic Heatmap)
Raster Color Ramping¶
See corresponding section of Kernel Density Estimation (Dynamic Heatmap)
Example mapfiles¶
MAP
SIZE 1000 500
EXTENT -180 -90 180 90
NAME "test heat"
IMAGETYPE "png"
WEB
METADATA
"ows_srs" "epsg:4326 epsg:3857 epsg:900913"
"ows_enable_request" "*"
END # METADATA
END # WEB
PROJECTION
"+init=epsg:4326"
END # PROJECTION
LAYER
NAME "idw"
TYPE raster
CONNECTIONTYPE idw
CONNECTION "points"
STATUS on
PROCESSING "IDW_RADIUS=20"
PROCESSING "IDW_COMPUTE_BORDERS=OFF"
PROCESSING "IDW_WEIGHT=1"
OFFSITE 0 0 0
CLASS
STYLE
COLORRANGE "#0000ff00" "#0000ffff"
DATARANGE 0 32
END # STYLE
STYLE
COLORRANGE "#0000ffff" "#ff0000ff"
DATARANGE 32 255
END # STYLE
END # CLASS
END # LAYER
LAYER
NAME "points"
STATUS on
TYPE POINT
DATA "pnts.shp"
END # LAYER
END # MAPFILE