Presentation at OGC GeoPackage working group

1. GeoPackage for
(lidar, top-down, tile-based)
Point Clouds
OGC TC Meeting
Michael P. Gerlek (RadiantBlue)
mpg@flaxen.com
1 June 2015
RadiantBlue 15 June 2015

2. Summary• No magic
– “Do the obvious thing”
• Yes, it’s actually a 2D model, not 3D
– LAS-centric
• Follows from raster tiling model
– Added “pctiles” data type
– Added new table for point dimensions
• Implemented in PDAL
5 June 2015 RadiantBlue 2

3. SQLite, etc.
• No changes to underlying tooling
• Not using spatial indexing
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4. Spatial Ref Sys Table
• (no change)
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5. Contents Table
• New data type: “pctiles”
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6. PCTile Matrix Set
• New table
– Taken directly from (Raster) Tile Matrix Set
• But no new fields
• Question
– Should this indeed be a separate table?
– Or should current (raster) table be overloaded
to allow point cloud tiles?
5 June 2015 RadiantBlue 6

7. PCTile Matrix
• New table
– Taken directly from (Raster) Tile Matrix
• Removed columns that don’t make sense for point
clouds (pixel space)
– tile_width, tile_height (in pixels)
– pixel_x_height, pixel_y_height (spatial)
• Question:
– Here too, could reuse existing (raster) table
– And just ignore the pixel field
– Or just redefine/overload tile_width/height
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8. “User Data” Table
• Added two new columns
– num_points
– child_mask
• Both helpful to clients (but not required)
– “How many points are available to be pulled
from the database for this tile?”
– “Which of this tile’s four child tiles are
available?”
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9. Blob Contents
• Packed set of points
– Each point is a packed set of dimensions
– Stored as native data types
• Example
– X0, Y0, Z0, T0, X1, Y1, Z1, T1, …
– f64, f64, f64, u64, f64, f64, f64, u64, …
• Optional compression via lazperf
– Standalone compression lib (think gzip)
– Derived from LAZ codec, datatype-aware
– (should be signaled in matrix set table or in metadata)
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10. Data Columns Table
• (not used)
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11. Metadata Table
• No schema change
• md_scope: “dataset”
• md_standard_uri: “LAS”
• mime_type: “text/plain”
• Need to define a convention
– (Or not)
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12. Metadata Reference Table
• No schema change
• reference_scope: “table”
• column_name: “table”
• row_id_value: “NULL”
• md_parent_id: “NULL”
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13. PCTile Dimensions Table
• New table
– Need to describe the “contents” of a “point”
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table_name TEXT NOT NULL PK,FK
ordinal_position INTEGER NOT NULL PK Lexical ordering of
the point structure
dimension_name TEXT NOT NULL “X”, “gps_time”, etc.
data_type TEXT NOT NULL “double”, “uint32”,
etc.
description TEXT
minimum, mean,
maximum
DOUBLEs Because histogram
stretch

14. Implementation Limitations
• Power-of-two zoom levels only
– And must start at 0
• Metadata protocol assumes LAS
– Quick hack
• Compression option not yet supported
• PDAL repo, rialto-tiling branch
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15. Some Minor Errata (OGC 12-128r10)
• Requirement 11
– A bit hard to parse – suggest “record” clauses be separated by semicolons
• Overloading of min_x, etc.
– Section 1.1.3.1.1
• Suggest explicitly stating that the bounding box is of the data and not the tile matrix set
– Section 2.2.6.1.1
• Suggest explicitly stating that the bounding box is of the tile matrix set and not the data
(although it is clear in subsequent 2.2.6.1.2)
• Table 14
– Reference to table 14 should be to table 15?
• Table 16 (column 1, row 4)
– Should be “row_id_value1” (superscript typo)
• Table 17
– Addition: table_name is an FK
5 June 2015 RadiantBlue 15

16. Thank you.
RadiantBlue 165 June 2015