Problems translating map file layers to mapscript

[Sean Gillies]

David,

On Oct 18, 2005, at 2:18 PM, David Niergarth wrote:

> Hi Sean,
>
>> No, the defaults are fine with mapscript. If you have turned on auto
>> label scaling, then you will need to set minsize and maxsize. 
>> Otherwise,
>> class.label.size controls all.
>
> When I set class.label.size = 8, I get one-pixel-tall labels. When I 
> set
> both class.label.minsize and class.label.maxsize to 8, I the labels I
> expect (but I have to set both max and min values). Is this perhaps
> because I'm building the whole layer from scratch in mapscript and 
> there
> are no initial values for those attributes? (This is similar to Damon's
> response.)
>
> We've been using ipython (a huge help) and the API docs to figure out
> how to create our custom layers.

I suspect that you might be doing something like this:

     class.label = mapscript.labelObj()

right? This could be your problem.

Instances of mapscript.classObj are **complete**. There is no need to 
create new attributes for them. A new instance of classObj already has 
a properly initialized labelObj as a "label" attribute. New instances 
of labelObj (as above) won't be properly initialized. That's just the 
way MapServer/mapscript is. Underneath the Python wrapper is a lot of C 
code which still presumes that we're parsing a mapfile.

Here's an example session:

Python 2.3 (#1, Sep 13 2003, 00:49:11)
[GCC 3.3 20030304 (Apple Computer, Inc. build 1495)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
 >>> import mapscript
 >>> c = mapscript.classObj()
 >>> c.label.minsize
4
 >>> c.label.maxsize
256

those are the normal defaults, and will give you working labels. Now, 
the problematic usage:

 >>> l = mapscript.labelObj()
 >>> l.minsize
0
 >>> l.maxsize
0
 >>>

this label is going to fail.

Rule of thumb: whenever an object has another object attribute with a 
single value (such as the label attribute of a classObj), that 
attribute will be created and initialize by the parent's constructor.

cheers,
Sean

--
Sean Gillies
sgillies at frii dot com
http://zcologia.com