Zsort ?

Daniel Morissette dmorissette at MAPGEARS.COM
Thu May 17 10:10:50 EDT 2007

Doesn't the sortshp command-line program allow you to do this already?

I am also worried that an ORDERITEM keyword/mechanism would be awfully 
slow on large shapefiles since the primary index used to fetch shapes on 
large files is the spatial index (.qix). There is currently no attribute 
index support on shapefile DBF's in MapServer and even if we added that, 
the primary index would remain the spatial index so I can't see how we 
could easily implement dynamic ordering of shapes without hurting 


Attila Csipa wrote:
> Maybe this would require a RFC, but I do not see this issue addressed in 
> existing .map references or RFC, I wanted to hear your opinion on this (there 
> was a short discussion about this, but a lot has changed in Mapserver since 
> then).
> What would you say if we introduced a drawing sort order inside layers ? As it 
> is now, all the features are drawn by their order in the data storage. If 
> using SQL queries one can define a sort order, but for shapefiles or other 
> local file storages this is not an option. This would mean introducing a sort 
> of ORDERITEM keyword (or an 'order' binding if we are thinking along the 
> lines of RFC19) which, if present, would be used to build a sorting table, 
> and then provide a seek function which would help the nextItem approach for 
> these data storages.
> The advantages of this should be obvious - for example if you have an area 
> column in your dbf you could draw large polygons first so you would not 
> obstruct small ones, or if you need to sort on a timestamp, etc.

Daniel Morissette

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