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The real-time projection of video and raster data for web maps

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The real-time projection of video and raster data for web maps

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The Real-time Projection of Video and Raster Data for Web Maps
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The Real-time Projection of Video
and Raster Data for Web Maps
Bojan Šavrič
Bernhard Jenny
ICA CoMP, Pittsburgh
October 5, 2014
Projecting with WebGL
Programs that are executed on the GPU
Vertex shader
(manipulate vertices of the geometry model)
Fragment shader
(determinate the color of image fragments)
Two approaches:
Inverse per-fragment projection
Combined forward per-triangle and
inverse per-fragment projection
Inverse Per-fragment Projection
Geometry: two triangles
7 steps for each fragment:
1)Dividing window coordinates by the nominal map scale
2)Subtracting false northing and false easting
3)Projection inverse converting Cartesian to spherical coord.
4)Rotating in the inverse direction
5)Adding the longitude of the central meridian
6)Converting spherical coordinates to UV texture
(scaling and shifting)
7)Sampling the fragment color from texture image
Aliasing artifacts Alpha blending
Forward Per-triangle Projection
Geometry: geographic-grid tessellation
Forward Per-triangle Projection
Geometry: geographic-grid tessellation
Forward Per-triangle Projection
Geometry: geographic-grid tessellation
Combined Forward Per-triangle…
Geometry: geographic-grid tessellation
5 steps for each fragment:
1)Forward projection of the geometry
(with applied map scale, false northing, and false easting)
2)Rotation spherical coordinates
3)Adding the longitude of the central meridian
4)Converting rotated coordinates to UV texture
5)Setting the flag if triangle is along the antimeridian
Combined Forward Per-triangle…
Anti-aliasing: Mipmaps
Anti-aliasing: Anisotropic Filtering
Thank you!
cartography.oregonstate.edu
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