[Thuban-list] RFC: Layer Classification

[Jan-Oliver Wagner]

On Thu, Jan 16, 2003 at 09:27:37AM -0500, Frank Warmerdam wrote:
> First, for non-ambiguous class membership for data ranges I would suggest
> the test semantics be "range_low <= value < range_high",

we'll apply this rule.

> Second, when classifying continuous values it is often convenient to
> have an aspect of the class (such as color) vary continuously depending
> on where the data value falls between range_low and range_high.  For
> instance, if rendering point data with temperatures it is often nice
> to have one class that continuously renders the points between blue and
> red depending on where they fall in a range.

it seems that there are three types:
	- discrete (eg 1,2,3 or 'ruin', 'city')
	- range (eg 0-2.5, 2.5-3.75, 3.75-65.123)
	- continous (as you described)

discrete and range is no problem and will be implemented first.
continous is a bit different since it couples a drawing property
(color, line thickness, ...) directly to the value.
Eg: range 1-15.6 corresponds to color (0,0,0)-(0,0,255)

Jonathan, I guess you should keep this third type of classification
in mind. Maybe it is not too complicated to implement it.

> Finally, you might want to introduce a concept of a NULL class.  The
> classification that should be applied to features not falling into another
> class.  Alternatively this might just be specified as a lowest priority
> class with a very wide data range.

This concept will be implemented.

-- 
Jan-Oliver Wagner               http://intevation.de/~jan/

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