class expressions in PHP/Mapscript

[Stephen Woodbridge]

There are lots of tools for working with shapefiles including
PHP/Mapscript. Check the maptools.org site and follow the link to
shapelib, there is a link to the ERSI spec on shapefiles and some other
links that might be of interest.

The short story is you can do most anything you like the the DBF except
change the order of the records, implicitly or explicitly. The DBF
records are associated to the shape records based on a one-to-one
correspondence of record numbers. ie: shape record 1 is related to dbf
record 1, etc.

So you can create a new dbf file and populate it with you values rename
the shapefile.dbf to shapfile.dbf-old and rename my-new.dbf to
shapefile.dbf and you already to try it out.

-Steve

Jeff Portwine wrote:
> Part of what I was asking , I really was making things too difficult... for
> my most zoomed out views I just took the national map file and used
> "expression  /Interstate/"  and "expression /US/" from the "NAME" field and
> this looks alright...  the hard part though is labeling them.   I thought
> like you said about re-writing the dbf file to add a field with route
> number, and I thought maybe I could have fields like "name", "alternate
> name
> 1", alternate name 2"  for roads that have multiple names and separate them
> on the comma to fill in those fields.   The only problem is I really don't
> know how to re-write a dbf file...  I don't have a problem writing a perl
> script or something like that but I just don't know much about how dbf
> files
> work, or how exactly they interact with the other parts of the shapefile
> and
> I wasn't sure if adding fields would throw off other parts of the shape
> file.
>
> I'll look into that more...   I was hoping there was a way I couild just
> use
> PHP to grab the number part of the "NAME" and use that as my label text
> somehow.
>
> Thanks,
> Jeff
>
> ----- Original Message -----
> From: "Stephen Woodbridge" <woodbri at swoodbridge.com>
> To: "Jeff Portwine" <jdport at VERITIME.COM>
> Cc: <MAPSERVER-USERS at LISTS.UMN.EDU>
> Sent: Monday, March 28, 2005 3:26 PM
> Subject: Re: [UMN_MAPSERVER-USERS] class expressions in PHP/Mapscript
>
>
>> Jeff,
>>
>> Since I suggested looking at this I take a stab at a response. I think
>> you
>> have done about the best you can given the data in its current state.
>> If I
>> were trying to work with that data, and I haven't looked at it yet, but
>> based on your description, I would be inclined to re-write the dbf
>> file as
>> something that would be more useful along the lines of
>>
>> New DBF fields:
>> NAME - suitable for labeling
>> RTE_NUM - number of route extract from the name
>> RTE_TYPE - I -interstate, S - state, U - US Highway, C - county highway
>> RTE_CLASS - maybe for classification of the road for style, but I think I
>> would just use RTE_TYPE for that.
>>
>> Then I can use CLASSITEM "RTE_TYPE", LABELITEM "NAME", and RTE_* for
>> highway shields.
>>
>> You would have to write a script to do this using Perl or PHP and regular
>> expressions, you would want to split multiple names on the "," and then
>> based on some higharchy populate the new fields.
>>
>> Or looks for some other data, like NHPN from the BTS.gov or whatever.
>>
>> I also find it useful to dump the various fields of a dbf and get a
>> unique
>> list of the options I am dealing with to better figure out how to deal
>> with it.
>>
>> Some days nothing is simple,
>> -Steve
>>
>> Jeff Portwine wrote:
>>
>>> I am trying to add a more "general" version of a "roads" layer to my
>>> maps
>>> that I could use instead of the Tiger line data while the maps being
>>> generated are not zoomed in.    When the maps are zoomed in closer I
>>> want
>>> to switch to the Tiger data and go from there.    I've downloaded a
>>> major
>>> roads layer from the national map website called "roadtrl20".   The
>>> problem is that it doesn't use fields like "CFCC" like tiger does, it
>>> simply has a "NAME" field and a "Feature" field.   The Feature field has
>>> strings like "Limited Access Highway Alternate Route", "Other Through
>>> HIghway", "Principle Highway", etc.... descriptions that are vague at
>>> best as they don't tell me if it is an interstate or  what.... and there
>>> are several descriptions that could be the same thing.
>>>  In the "Name" field, it has things like  "Interstate Route 1",  "State
>>> Route", "US Route", etc... which is a little more useful except again
>>> there are several versions of things like "Interstate"  (Alternate
>>> Interstate, Business Interstate, etc)  and to make it more complicated
>>> many of them show several names separated by comma's.     So, it's
>>> difficult to come up with a good expression to separate the different
>>> types of roads... I thought I could do it in mapscript just reading the
>>> different "Names" into a variable and manipulating that variable to give
>>> me one word like "Interstate", "State", "US" that I could then use in my
>>> "expression" clause.    I thought I could do something similar to get
>>> the
>>> route number alone to use for labeling purposes (I'd like to superimpose
>>> the route # on a graphic of an interstate sign, etc).     I can't see
>>> any
>>> methods though that allow me to access the information from the
>>> shapefile
>>> to do this..    Is this possible, or am I just making this a lot more
>>> complicated that I need to?
>>>  Thanks,
>>> Jeff
>>>
>>
>>
>