SfM Workflow

Libraries and notebooks for processing SfM xyzrgb data.

PDAL Configuration (PDAL.py)

The PDAL.py file contains the PDAL Object specification. This object provides functions for generating json-formatted PDAL workflows that will crop, rotate, and translate an sfm point cloud.

Creating a PDAL object

Here's an example that demonstrates how a PDAL configuration can be generated from a set of points. The points are provided as a list of [x,y] pairs (i.e. a list of lists):

points = [
    [262986.2, 53128.25],   # lower right corner of crop area
    [262967.5, 53029.84],   # lower left corner of crop area  
    [262870.1, 53048.72],   # upper left corner of crop area
    [262888.9, 53148.19],   # upper right corner of crop area 
]

Note: The points supplied must be in circular (clockwise or counterclockwise) order for the correct configuration file to be generated.

Using these points, we can import the PDAL class, and initialize a PDAL object:

from PDAL import PDAL

my_pdal = PDAL(points=points)

The my_pdal object can now be used to generate the appropriate PDAL configuration file.

Creating a PDAL configuration file

The PDAL configuration file is a JSON-formatted file created using the PDAL.write_json() function. The defaut name for this file is sfm_cloudprocess.json, but this can be overridden by passing an output_file argument when generating a pdal object:

my_pdal = PDAL(points=points, output_file=`name_of_output_file.json`)

my_pdal.write_json()

Alternatively, it is possible to specify the output file when calling write_json():


my_pdal.write_json(output_file='name_of_output_file.json')

Writing output files with one-liners:

It is possible to write out a PDAL configutation file using only an array of points:


points = [
    [262986.2, 53128.25],   # lower right corner of crop area
    [262967.5, 53029.84],   # lower left corner of crop area  
    [262870.1, 53048.72],   # upper left corner of crop area
    [262888.9, 53148.19],   # upper right corner of crop area 
]

PDAL(points=points).write_json()

Note: As with the note above, these points supplied must be in circular (clockwise or counterclockwise) order for the correct configuration file to be generated.

Additional Class functions

The PDAL class has a suite of functions that assist in working with PDAL calculations these include:

PDAL.rotation_angle(points): Determines the necessary rotation angle, given a list of bounding coordinates.
PDAL.rotation_matrix(points): Generates the appropriate transformation matrix necessary to rotate a set of points into an orthogonal coordinate system.
PDAL.translation_matrix(points): Generates the transformation matrix necessary to re-center a transformed matrix so that the lower left corner of the point cloud is at the origin (0,0)
PDAL.transform_point(point, matrix): Re-projects a single point according to a specified transformation matrix (use PDAL.rotation_matrix() or PDAL.translation_matrix() to generate this matrix)

TODOS: