Re: [Geotools-gt2-users] Choropleth map legend

[Hal M. <hm...@as...>]

Andy,

The classification and legend was a bit tricky ...

I've attached an implementation of the Jenks algorithm for your
consideration.  It can be used to classify your features.  

	Map<FeatureId, Double> densities = new HashMap<FeatureId, Double>();

	... calculate densities ...

	ClassificationFunction classify = new JenksNBFunction();
	ArrayList<Expression> params = new ArrayList<Expression>();
	params.add(ff.property("name"));
	params.add(ff.literal(4));
	classify.setParameters(params);
		        
	RangedClassifier groups = (RangedClassifier)
classify.evaluate(densities);

You can get the min/max foreach range from groups

Also consider a map of class number to color.  From there I styled my
feature layer by creating a set of rules, each rule containing a filter of a
set of feature IDs and a symbolizer tied to a color (from the color lookup
map).

Hal

-----Original Message-----
From: Andy Turner [mailto:A.G...@le...] 
Sent: Wednesday, November 26, 2014 5:51 PM
To: 'Hal Mirsky'; geo...@li...
Subject: RE: [Geotools-gt2-users] Choropleth map legend

Thanks Hal,

I tried making a class by extending DirectLayer.

I tried adding it as a layer to the MapContent. It does something, but I
have not figured out what as yet...

I'm going to work on this tomorrow. It is most important for me that I can
get the bounds for each of the classes. Ideally I would like to produce a
legend, but at the moment I haven't found a way of getting the values
back... Hopefully I will find a way tomorrow, but if anyone has any further
pointers, that would be great.

Cheers,

Andy


-----Original Message-----
From: Hal Mirsky [mailto:hm...@as...] 
Sent: 25 November 2014 22:22
To: Andy Turner; geo...@li...
Subject: RE: [Geotools-gt2-users] Choropleth map legend

Andy,
I derived a class from DirectLayer and implemented the draw method which
worked great.  

Some of the legend text was dynamic (e.g. low/high values for each color).
A little interesting to figure out the size of rectangles I needed to draw
for each legend item.  Here's a snippet:

private Font titlef = new Font("Ariel", Font.BOLD, 12); private Font itemf
= new Font("Ariel", Font.BOLD, 10);

Rectangle2D titleLabelRect = titlef.getStringBounds(title, new
FontRenderContext(null, RenderingHints.VALUE_TEXT_ANTIALIAS_DEFAULT,
RenderingHints.VALUE_FRACTIONALMETRICS_DEFAULT));

Rectangle2D itemLabelRect = itemf.getStringBounds(label, new
FontRenderContext(null, RenderingHints.VALUE_TEXT_ANTIALIAS_DEFAULT,
RenderingHints.VALUE_FRACTIONALMETRICS_DEFAULT));

// now get the height of the title rectangle and height to use for each
legend item:

th = (int) titleLabelRect.getHeight();
ih = (int) itemLabelRect.getHeight();  // height of site label.  Also used
as icon size	
 ...

Hope this helps,
Hal
-----Original Message-----
From: Andy Turner [mailto:A.G...@le...]
Sent: Tuesday, November 25, 2014 11:36 AM
To: geo...@li...
Subject: [Geotools-gt2-users] Choropleth map legend

Hi,

I would like to have a map legend for the choropleth maps I am generating,
please will you help?

To style the main part of the map I have followed an example using
ColorBrewer and FilterFactory2. I have a Classifier by calling evaluate on a
Function from the FilterFactory2.

I've have searched and found others asking about this [1], but no answers.

[1]
http://gis.stackexchange.com/questions/22962/create-a-color-scale-legend-for
-choropleth-map-using-geotools-or-other-open-sou

Thanks,

Andy
http://www.geog.leeds.ac.uk/people/a.turner/index.html
 


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