Changes between Initial Version and Version 1 of MapGuideRfc159

Timestamp:

Jun 6, 2017, 5:56:06 AM (7 years ago)

Author:

jng

Comment:

--

MapGuideRfc159

@@ +1 @@
+
+= !MapGuide RFC 159 - UTFGrid support =
+
+This page contains a change request (RFC) for the !MapGuide Open Source project.
+More !MapGuide RFCs can be found on the [wiki:MapGuideRfcs RFCs] page.
+
+== Status ==
+
+||RFC Template Version||(1.0)||
+||Submission Date||6 Jun 2017||
+||Last Modified||6 Jun 2017||
+||Author||Jackie Ng||
+||RFC Status||ready for review||
+||Implementation Status||Pending||
+||Proposed Milestone||3.3||
+||Assigned PSC guide(s)||(when determined)||
+||'''Voting History'''||(vote date)||
+||+1||||
+||+0||||
+||-0||||
+||-1||||
+||no vote|| ||
+
+== Overview ==
+
+This RFC proposes to add support for the rendering and storage/retrieval of UTFGrid tiles
+
+== Motivation ==
+
+UTFGrid is a compact JSON-based specification for storing rasterized interaction data and nicely complements XYZ map tiles.
+
+Where XYZ tiles provide the visuals, UTFGrid provides the tooltip interaction data. Combined together, you can have powerful 
+interactive tiled maps that require no sessions or server roundtrips for tooltip data as they can be queried locally from the UTFGrid tile.
+
+For a more in-depth overview of UTFGrid see: https://www.mapbox.com/blog/how-interactivity-works-utfgrid/
+
+== Proposed Solution ==
+
+This RFC will implement version 1.3 of the UTFGrid specification.
+
+Add a new API to MgRenderingService for the rendering of UTFGrid tiles.
+
+{{{
+class MG_MAPGUIDE_API MgRenderingService : public MgService
+{
+PUBLISHED_API:
+    /////////////////////////////////////////////////////////////////
+    /// \brief
+    /// Returns the specified UTFGrid tile for the given map. Tile structure is
+    /// based on the XYZ tiling scheme used by Google Maps, OpenStreetMap, and
+    /// others
+    ///
+    /// \param map
+    /// Input
+    /// map object containing current state of map.
+    /// \param baseMapLayerGroupName
+    /// Input
+    /// Specifies the name of the baseMapLayerGroup for which to render the tile.
+    /// \param x
+    /// Input
+    /// Specifies the row index of the tile to return.
+    /// \param y
+    /// Input
+    /// Specifies the column index of the tile to return.
+    /// \param z
+    /// Input
+    /// Specifies the zoom level of the tile to return.
+    /// \param dpi
+    /// Input
+    /// Specifies the dpi of the tile to return.
+    /// \param tileImageFormat
+    /// Input
+    /// Specifies the image format of the tile to return.
+    ///
+    /// \return
+    /// A byte reader containing the rendered UTFGrid tile.
+    ///
+    /// \since 3.3
+    virtual MgByteReader* RenderTileUTFGrid(
+        MgMap* map,
+        CREFSTRING baseMapLayerGroupName,
+        INT32 x,
+        INT32 y,
+        INT32 z,
+        INT32 dpi) = 0;
+};
+}}}
+
+The server-side implementation of this API taps into a new UTFGrid renderer in the Renderers project. The UTFGrid renderer uses the existing AntiGrain Geometry (AGG) library to render "pixels" of UTF characters. 
+
+To avoid unnecessary reinventing of the wheel, our UTFGrid renderer implementation re-uses MapServer's [implementation of the low-level AGG pixel primitives](https://github.com/mapserver/mapserver/blob/branch-7-0/maputfgrid.h) needed to render UTF character "pixels"
+
+We will leverage the infrastructure introduced in RFC 140 to add support for UTFGrid tiles.
+
+Support for UTFGrid tiles is exposed through the new {{{TileFormat}}} of {{{UTFGRID}}} in the existing {{{XYZ}}} tile provider. 
+
+Retrieval of UTFGrid tiles is achieved through the existing {{{GETTILEIMAGE}}} mapagent operation version {{{1.2.0}}}, with the {{{MAPDEFINITION}}} parameter pointing to a Tile Set Definition resource configured:
+
+ * With the {{{XYZ}}} tile provider
+ * With the {{{TileFormat}}} of {{{UTFGRID}}}
+
+For this RFC, UTFGrid rendering takes the following into consideration:
+
+ * It only looks at layers in the Tile Set that have a tooltip and/or URL defined in their Layer Definition
+ * Tooltip and Hyperlink content for features in these matching layers are rendered out as the following properties:
+    * {{{MG_TOOLTIP}}}: The tooltip content for the feature
+    * {{{MG_URL}}}: The associated hyperlink for the feature
+
+Thus, if you have a Tile Set configured with a {{{TileFormat}}} of {{{UTFGRID}}}, but have no layers that have tooltips or hyperlinks defined in their respective Layer Definitions, the UTFGrid tiles rendered and retrieved from such a Tile Set Definition will be blank.
+
+This implementation resides in the [http://trac.osgeo.org/mapguide/browser/sandbox/jng/utfgrid utfgrid sandbox]. Upon adoption of this RFC, it will be merged into trunk.
+
+== Implications ==
+
+A Tile Set Definition using the {{{XYZ}}} provider and a {{{TileFormat}}} of {{{UTFGRID}}} can only be used on versions of MapGuide on/since the introduction of this RFC.
+
+== Test Plan ==
+
+Add unit tests for rendering UTFGrids, compare with image-based XYZ tiles at the same X/Y/Z coordinates for "visual" verification of UTFGrid content.
+
+== Funding / Resources ==
+
+Community