MapGuide RFC 69 - Rendering Layer Styles using Style Order

This page contains an change request (RFC) for the MapGuide Open Source project. More MapGuide RFCs can be found on the RFCs page.

Status

RFC Template Version	(1.0)
Submission Date	Jun 26 15:40:00 2009
Last Modified	Zac Spitzer Timestamp
Author	Zac Spitzer
RFC Status	proposed
Implementation Status
Proposed Milestone	2.2
Assigned PSC guide(s)

Overview

Correct rendering of road networks requires ordering. Major roads should be rendered over the top of minor roads.

Motivation

Currently MapGuide Studio exposes the ability to order individual styles within a layer,
however, the server doesn't support ordered rendering.

There are three possible known work arounds:

1. Break the road networks into separate layers.
   
2. Render the roads using composite type styles and specify the RenderingPass appropriately (see ​RFC 29 for details).
   
3. Set up the data source so that it returns readers with the features in the correct draw order.
   

Adding support to respect this ordering is considered to resource expensive, as many individual queries would be required.

Proposed Solution

Add support to the rendering engine to render layer styles in ordered passes.

After some discussion, it appears that implementing ordering of results from FDO could be an efficient way of approaching this. This avoids requiring MapGuide to issue multiple FDO queries.

The question has been raised about the support for ordering within other providers such as SHP and FDO.

This would require a change to FDO ​http://trac.osgeo.org/fdo/wiki/FDORfc40

As this will add overhead, by taking the ordered approach, this could be turned on by an optional field defining ORDER BY column(s) in the layer definition .

Implications

The current approach is to make this an optional enhancement, as to avoid impacting all layers.

Test Plan

None.

Funding/Resources

Help wanted

Related Trac Tickets

​http://trac.osgeo.org/fdo/wiki/FDORfc40 #618 Theming stylisation order isn't respected in a layer
​FDO Core enhancment: support standard ORDER BY expressions

Discussions

​http://n2.nabble.com/MapGuide-RFC-69---Rendering-Layer-Styles-using-Style-Order-td3158848.html
​http://n2.nabble.com/RE%3A-MapGuide-RFC-69---Rendering-Layer-Styles-td3159460.html