Back when Adam Golding and I prototyped Probability Mapper we already had an algorithm that could give the probability based on distance, terrain, vegetation, and other factors. But we were working with raster images, so we only had distance. If you had vector layers for terrain & vegetation, you'd be set.
~Originally 9 June 2008
Example from Feature Analyst's Landcover Tutorial
But suppose you don't. How do you take a raster image (above left) and turn it into a set of vector polygons (above right)? It's too tedious to do by hand. We thought about making a classifier, but that sounded like a side project that would expand without end. A recent email exchange brought it to mind again, and I did some looking. It seems there are good solutions out there, if you can pay.
On April 4, I attended a demo by ESRI at GMU. At one stage, they had to count the number of tailings cones (dirt piles) that had been excavated from a runway, to see if the volume of dirt matched the cut-and-fill operation, or if there was extra dirt suggesting underground facilities. Rather than manually count the thousands of piles, they used Definiens eCognition software to circle several and say "this is what I want". That trained a classifier, which went and found all the rest of them, and returned a vector layer for the piles.
Feature Analyst seems to be quite capable, using context and some pretty nifty machine learning. The examples and customers specifically mention Landcover classification. (See the example image above.)
Programmers looking for a smaller(?) package may be interested in the targeted ad suggested by gMail during my previous email exchange: Berkeley ImgSeg. It appears to do the same thing: you train a classifier by pointing to "yes" and "no" areas, it learns, and then it classifies your image for you. The appear to have a Python API, which gets points in my book.
Bayesian Network Classifiers
Ed Wright, my GIS colleague at IET has developed probabilistic feature classifiers by embedding our company's Bayes Net engine into a major image processing package. So far as I know, the GIS company hasn't been convinced there is a market for this sort of thing, and has not released it. (Also, for all we know, Feature Analyst might use similar technology. The nice results it seems to be getting are a hallmark of Ed's multi-layer, context-based approach.)
- Is anyone using this for Search & Rescue? Care to comment, esp. on "real-time" use in a mission?
- Is adequate vector data available?
- Is there a good open-source equivalent?
Bob reminds me that the NLCD classifications are available directly, so for broad-strokes classification of 30m squares, we don't have to extract features: Charles: In regards to classify land. What I used in the book was NLCD which is available for free. It was taken from Landsat data, so in some cases it may be a bit dated. But for wilderness searches it is probabily ok. If I recall the resolution is a 30 meter square at best. Other coarser resolution are available. But I know I could look at the data easily using tools on the web. So I think that would be the quick and dirty.
Plenty of info on the web.
It is one of the models I mention in the book, that should be used for predicting POA.
Jim writes: The Feature Analyst is one of the best out there for the ESRI platform. The company (VLS) got its start through a NASA SBIR. Naive Bayesian classifiers have been used lots in the remote sensing realm.