Some doc updates for filters.reprojection and others

doc/stages/filters.reprojection.rst

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+.. _filters.reprojection:
+
+filters.reprojection
+===========================
+
+The reprojection filter converts the X, Y and/or Z dimensions to a new spatial
+reference system. The old coordinates are replaced by the new ones,
+if you want to preserve the old coordinates for future processing, use a
+`filters.ferry`_ to create a new dimension and stuff them there.
+
+.. note::
+
+    X, Y, and Z dimensions in PDAL are carried as doubles, with their
+    scale information applied. Set the output scale (`scale_x`, `scale_y`, or
+    `scale_z`) on your writer to descale the data on the way out.
+
+    Many LIDAR formats store coordinate information in 32-bit address spaces, and
+    use scaling and offsetting to ensure that accuracy is not lost while fitting
+    the information into a limited address space. When changing projections, the
+    coordinate values will change, which may change the optimal scale and offset
+    for storing the data.
+
+
+Example
+-------
+
+.. code-block:: xml
+
+  <?xml version="1.0" encoding="utf-8"?>
+  <Pipeline version="1.0">
+    <Writer type="drivers.las.writer">
+    <Option name="filename">example-geog.las</Option>
+    <Option name="scale_x">0.0000001</Option>
+    <Option name="scale_y">0.0000001</Option>
+    <Option name="scale_z">0.1</Option>
+    <Option name="offset_x">-100</Option>
+    <Option name="offset_y">40</Option>
+    <Option name="offset_z">0</Option>
+    <Option name="spatialreference">EPSG:4326</Option>
+      <Filter type="filters.reprojection">
+        <Option name="in_srs">EPSG:26916</Option>
+        <Option name="out_srs">EPSG:4326</Option>
+        <Reader type="drivers.las.reader">
+          <Option name="filename">example-utm.las</Option>
+          <Option name="spatialreference">EPSG:26916</Option>
+        </Reader>
+      </Filter>
+    </Writer>
+  </Pipeline>
+
+Options
+-------
+
+in_srs
+  Spatial reference system of the input data. Express as an EPSG string (eg
+  "EPSG:4326" for WGS86 geographic) or a well-known text string. [Required if
+  input reader does not supply SRS information]
+
+out_srs
+  Spatial reference system of the output data. Express as an EPSG string (eg
+  "EPSG:4326" for WGS86 geographic) or a well-known text string. [Required]
+