about line joins and their z-order

[Jackey Cheung]

Thanks for your confirmation of the drawing order, and your advise.

I'll take the 2nd work around, since the 1st one makes the lines disjoined.

  ----- Original Message ----- 
  From: Rodrigo Martín LÓPEZ GREGORIO 
  To: Jackey Cheung 
  Cc: MAPSERVER-USERS at lists.umn.edu 
  Sent: Saturday, June 16, 2007 11:00
  Subject: Re: [UMN_MAPSERVER-USERS] about line joins and their z-order


  I assume that both (yellows and whites) roads are in the same layer and different classes. If this is the case you have no control about the drawing order with the class elements. Mapserver renders all layer elements in the order it gets from source (shp, postgis). 

  I think there can be two alternatives. The first is separate the roads in two layers using a FILTER at LAYER level so all the white roads gets drawed first and then all the yellow ones.

  The other alternative (the one I have used sometime) is order the elements in the source (shp, postgis) so all white elements are procesed first by mapserver. If your layer DATA is on a PostgreSQL table then you can make a second table with the same structure of your original table and insert all the roads in the right order like: 

  INSERT INTO newtable SELECT * FROM oldtable ORDER BY criteria

  I'm sure there must be a better way to sort the elements without creating a second table but this is the way I get it work.

  If your layer DATA is on a shp file I don't know how to do that but the idea is the same so if you find the way to do the same on shp file it must work also. 

  Rodrigo.


  On 6/15/07, Jackey Cheung <cheung.jackey at gmail.com > wrote: 
    I've rendered a map image like this: http://www3.mapasia.com/jackout/rj.png

    there are a few problems here:

    1. they are joined correctly
    2. although they are joined, but the yellow one should "covers" the white ones
    3. the white one should be drawn beneath the lower segment of the yellow one

    As trying to fix this kind of problems, I've noticed that it's impossible to control the z-order of how roads are drawn. Say, in may cities, one very long road may elevated somewhere, and dive beneath other roads somewhere else. Is there any way to present this kind of thing with MapServer?

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