The class GeoFeatureDialog provides a tool for computing statistical descriptors of geographical regions computed from
raster-based information about a geographical area, for example, raster-based information about elevation.
The tool fuses raster (e.g., elevation) and vector (e.g., county boundaries) data using georeferencing
information, displays overlaid data, computes statistics over each boundary and reports results in a DBF file, as well as
in a visual form .
Description:
The tool is designed to calculate mean, standard deviation, skew and kurtosis of raster-based
geographical features per each geographical boundary. Raster-based features are represented as an image
with multiple bands and geographical boundaries are represented as vectors of points
loaded from the ESRI shape file. It is assumed that raster and vector data are also described with
georeferencing information so that the two data sets can be fused.
Setup:
Once raster information was loaded into the main window, region boundaries should be loaded freom an ESRI shape file by clicking
on "LoadShape".
The loaded shape file can have its points specified either in pixels or in latitude/longitude. If the shape file points are described in terms of latitude/longitude,
then the user MUST select the option to convert the latitude/longitude to pixels. If such a conversion is required,
the underlying image MUST have geo-specific information to allow this conversion of shape file points.
For instance, if the underlying image is a digital elevation map (or DEM image),
its associated header file may contain information like the UTM Northing and Easting insertion values and the column and row resolution.
Using these geo-specific values, standard georeferencing conversions (defined in GeoConvert class) are applied to convert points from latitude/longitude co-ordinate system
to pixel co-ordinate system.
The loaded boundaries can be viewed by clicking on the button "ShowShape". If one would like to view the centroid points
of all boundaries then the button "Show Centroid Points" will overlay centroid points on the image. Before showing the overlay of boundaries
on top of the image (raster-based information), the two data sets (boundary points and image pixels)
are georegistered based on their georeferencing information.
Georegistration involves conversion of boundary points in latitude/longitude to boundary points in pixel coordinates and is performed
automatically when either of "ShowShape" button or "Compute" button is initiated. This conversion is performed only once because
the computation is very expensive.
Since a shape file could have many points that do not even fall on the image, it is wasteful to convert all shape points to pixels.
One of the optimizations done during this conversion process is to convert only those points that actually lie on the underlying image.
The algorithm works by first checking which boundaries of the shapes defined in the shape file,
overlap or lie entirely within the underlying image's boundary. Only for those particular boundaries, the
points are converted from latitude/longitude value to x/y pixel value.
A new shape object with a new set of relevant points is constructed using this procedure.
After this optimization, all other methods in this tool work only on the reduced set of shape points.
This gives considerable speedup.
Inputs required to run the tool:
The following inputs are required to run the tool:
1. The image on which the shape file will be overlaid.
2. The shape file which needs to be overlaid on the image loaded in the previous step.
If the shape file points are described in latitude/longitude, the underlying image must have geo-specific information
to allow conversion of shape points from latitide/longitude to pixel. To indicate that this conversion is required, the
'Enable lat/lng to pixel conversion' radio button must be selected.
Step 1: An image must be loaded in the main image window. This is the image on which the user wants overlay a shape on that image and perform various computation.
Step 2: Click 'Load Shape'. At this time the user must decide whether to enable or disable the 'lat/lng to pixel conversion' option,
as it will affect all future computations on the loaded shape.
Step 3:One can click 'Show Shape' to view the loaded shape overlaid on the underlying image. If there is no overlap between the loaded shape
and the image, then a 'No overlay found' message is displayed to the user.
Step 4:If an overlap was found in Step 3, the user can click 'Compute' to initiate computing all the four statistics mentioned earlier.
Step 5:Using the combo-box 'Select Feature', the user can then select the statistical feature he wants to view.
'Show Results' can then be clicked to get a color coded image for the the selected feature.