pointcloud/doc/concepts/objects.rst

.. _objects:

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Point Cloud Objects
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PcPoint
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The basic point cloud type is a ``PcPoint``. Every point has a (large?) number of
dimensions, but at a minimum an X and Y coordinate that place it in space.

Points can be rendered in a human-readable JSON form using the
``PC_AsText(pcpoint)`` function. The "pcid" is the foreign key reference to the
``pointcloud_formats`` table, where the meaning of each dimension in the "pt"
array of doubles is explained. The underlying storage of the data might not be
double, but by the time it has been extracted, scaled and offset, it is
representable as doubles.

.. code-block:: sql

    {
        "pcid" : 1,
          "pt" : [0.01, 0.02, 0.03, 4]
    }

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PcPatch
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The structure of database storage is such that storing billions of points as
individual records in a table is not an efficient use of resources. Instead, we
collect a group of ``PcPoint`` into a ``PcPatch``. Each patch should hopefully
contain points that are near together.

Instead of a table of billions of single ``PcPoint`` records, a collection of
LIDAR data can be represented in the database as a much smaller collection (10s
of millions) of ``PcPatch`` records.

Patches can be rendered into a human-readable JSON form using the
``PC_AsText(pcpatch)`` function. The "pcid" is the foreign key reference to the
``pointcloud_formats`` table.

.. code-block:: sql

    {
        "pcid" : 1,
         "pts" : [
                  [0.02, 0.03, 0.05, 6],
                  [0.02, 0.03, 0.05, 8]
                 ]
    }