Changes between Version 24 and Version 25 of MapGuideRfc51


Ignore:
Timestamp:
Sep 24, 2008, 1:29:39 PM (16 years ago)
Author:
chrisclaydon
Comment:

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  • MapGuideRfc51

    v24 v25  
    7676We will support re-projecting raster in drawing sources.
    7777
    78 === Addendum ===
    79 
    80 When we came to implement this proposal, it became apparent that we would achieve better results by generating the grid in the raster coordinate system and transforming it into the map coordinate system, rather than the other way round (as originally proposed). A description of the new method follows:
    81 
    82 In Figure 1, the blue rectangle represents the current map (or viewport) extents. The extents are converted from the map coordinate system into the raster coordinate system in order to determine the new extents in the raster CS (green rectangle).
    83 
    84 ||[[Image(MapToLayerCS.png)]]||
    85 ||Figure 1. Conversion of map (or viewport) extents into raster coordinate system.||
    86 
    87 The intersection of the raster extents (pink) with the map extents (green) is then calculated in the raster coordinate system. And this part of the raster image is retrieved from the provider (yellow).
    88 
    89 ||[[Image(MapRasterIntersection.png)]]||
    90 ||Figure 2. Intersection of map and raster in raster CS.||
    91 
    92 The raster image is then divided into a mesh of tesselating triangles. The vertices of the mesh are transformed from raster pixel coordinates into the raster coordinate system coordinates, then into the map (or viewport) coordinate system coordinates, and finally into map pixel coordinates, to create a transformed non-uniform mesh. Each triangle from the source raster is then rendered into the corresponding triangular section in the destination mesh to produce the transformed raster image.
    93 
    94 ||[[Image(MeshReprojection.png)]]||
    95 ||Figure 3. The raster image is rendered into the viewport using the transformation mesh.||
    96 
    9778== Implications ==
    9879
    … …  
    11596
    11697Autodesk
     98
     99== Addendum ==
     100
     101When we came to implement this proposal, it became apparent that it would be more efficient to generate the grid in the raster coordinate system and transform it into the map coordinate system, rather than the other way round (as originally proposed). A description of the new method follows:
     102
     103In Figure 1, the blue rectangle represents the current map (or viewport) extents. The extents are converted from the map coordinate system into the raster coordinate system in order to determine the new extents in the raster CS (green rectangle).
     104
     105||[[Image(MapToLayerCS.png)]]||
     106||Figure 1. Conversion of map (or viewport) extents into raster coordinate system.||
     107
     108The intersection of the raster extents (pink) with the map extents (green) is then calculated in the raster coordinate system. And this part of the raster image is retrieved from the provider (yellow).
     109
     110||[[Image(MapRasterIntersection.png)]]||
     111||Figure 2. Intersection of map and raster in raster CS.||
     112
     113The raster image is then divided into a mesh of tesselating triangles. The vertices of the mesh are transformed from raster pixel coordinates into the raster coordinate system coordinates, then into the map (or viewport) coordinate system coordinates, and finally into map pixel coordinates, to create a transformed non-uniform mesh. Each triangle from the source raster is then rendered into the corresponding triangular section in the destination mesh to produce the transformed raster image.
     114
     115||[[Image(MeshReprojection.png)]]||
     116||Figure 3. The raster image is rendered into the viewport using the transformation mesh.||
     117