[mapserver-dev] general problem with bar charts

[Karsten Hoffmann]

Hi developers,

 

I’m not sure if somebody has already recognized the following problem.

I found out that the bar charts in mapserver 5.0 are not really useful for
thematic mapping. Bar charts of different features in a map are not
comparable with each other because the maximum values in each chart have the
same size (height).

 

For example I have two features with the following attributes:

Feature A: 1000, 500, 200

Feature B: 2000, 1000, 400

 

Both features have exactly the same bar chart in the same size (height)
which I have defined for example with PROCESSING "CHART_SIZE=30 40". This
gives a wrong map and a wrong impression to the map reader. The height of
the bars of Feature A should only be the half of the bars heights of Feature
B.

 

My impression is that the maximum value of the given attributes for one
feature is always drawn with the defined height. All other values in this
chart are drawn relative to this height. 

 

It would be better to define a global height for a value (for example 30
pixels is equivalent to 2000). All bars of all charts should then be drawn
relative to this definition.

 

Another very useful function for thematic mapping would be the possibility
to vary the size (diameter) of pie charts relative to an attribute or the
sum of the values which are used for drawing the pie slices.

But I found out that this is already in the works and will hopefully come
with version 5.2 (see http://trac.osgeo.org/mapserver/ticket/2136).

 

Best regards,

Karsten Hoffmann

--

Dipl.-Geogr. Karsten Hoffmann

Institut für Geoinformatik und Fernerkundung (IGF)

Universität Osnabrück

Seminarstr. 19 a/b

49069 Osnabrück

 

Raum: 02/106

Tel.: +49 541 969-4233

Fax:  +49 541 969-4061

E-Mail: khoffmann at igf.uni-osnabrueck.de

Web:  www.igf.uni-osnabrueck.de

 

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