owlet 0.8.3

A Geospatial Python Package for Field Researchers

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A Geospatial Python Package for Field Researchers

Owlet and EGF: Developed for Field Researchers

Owlet is a Python library for interacting with and mapping EGF files.

EGF, or Exact Geometry Format, is a file structure designed specifically for recording geo-data without traditional GIS software. An EGF file contains all of the necessary components required to define geospatial features— without overcomplicating it.

EGF File Example

Overview

An EGF file is comprised of three sections:

1. A Feature Type Declaration (point, line, polygon)
2. Attribute Headers
3. Features: attributes & coordinate sets

Example EFG file containing two placemarks:

PT



Park Name, City, Pond, Fountain



Post office Square, Boston, FALSE, TRUE
42.356243, -71.055631, 2



Boston Common, Boston, TRUE, TRUE
42.355465, -71.066412, 10

In an EGF file, each section / feature is separated by three blank lines and the file ends with a single blank line.

An EGF file is a '.txt' file renamed to '.egf'

Full EGF Documentation

Installing Owlet

To install owlet, type one of the following commands into the terminal or command line

Windows

>>> py -m pip install owlet

MacOS / Linux

>>> pip3 install owlet

Using Owlet

To begin, save the EGF file example above to your computer as BostonParks.egf using a text editor such as Notepad.

Once the EGF file is saved, create a new Python file and import Owlet.

When writing a new Python file, begin by importing Owlet.

import owlet

Reading an EGF file

To read an EGF file, begin by saving the path of the EGF file to a variable in your python script.

Then pass the variable that hold the EGF file's path to the read_egf() function. Since the read_egf() function is a part of the Owlet Python package, the function is called by typing owlet. before the function name - e.g. owlet.read_egf()

Below, the EGF file is loaded and saved to a variable named my_shape.

in_file = "path/to/file/BostonParks.egf"

my_shape = owlet.read_egf(in_file)

If the file path is short, it may be easier to pass the path directly in to the function like in the example below. For longer paths, it is neater to save the path to a variable.

my_shape = owlet.read_egf("folder/BostonParks.egf")

Visualizing an EGF file

To visualize my_shape, call the visualize() function and pass my_shape to it.

owlet.visualize(my_shape)

Upon visualize() being executed, the computer's default web browser will open and provide a preview of my_shape using the webpage geojson.io

Both points from the EGF file are displayed on the map after running owlet.visualize(my_shape)

EGF Files also support linestrings for mapping paths

Polygons are also supported by EGF

Converting an EGF File to Other Formats

To interact with the data from an EGF file outside of Owlet, the data can be exported to a different format. Owlet offers a few different export options.

GeoJSON

To use the EGF data with other GIS software packages, Owlet provides a GeoJSON export option.

To export data in GeoJSON format, first save the export file path to a variable. (Notice that the new file's name and file extension are included in the path.)

Then call the function write_geojson() and pass it the path of the file to be created as well as the variable that holds the EGF geometry.

out_file = "folder/MyShape.json"

owlet.write_geojson(out_file, my_shape)

Upon write_geojson() being executed, a .json file will be created at the location specified by the path defined by the out_file variable. The new GeoJSON file can be loaded, viewed, and manipulated by many common GIS programs.

Loading GeoJSON into Owlet

in_file = "path/to/file/MyShape.json"

my_shape = owlet.read_geojson(in_file)

Note: Owlet has the ability to read GeoJSON files where each feature is of the same geometry type and every feature is contained within a "FeatureClass" (QGIS exports GeoJSON files in this format). Owlet supports Point, LineString, and Polygon GeoJSON features only. A GeoJSON file may have either .json or .geojson as its file extension.

Reading an EGF file and Writing it to a GeoJson File - Complete Script

import owlet

in_file = "path/to/file/BostonParks.egf"
out_file = "folder/MyShape.json"

my_shape = owlet.read_egf(in_file)

owlet.write_geojson(out_file, my_shape)

CSV

To view/manipulate an EGF file in as a table, the write_csv() function can be used in the same way as the write_geojson() function.

To export data in CSV format, first save the export file path to a variable. (Notice that the new file's name and file extension are included in the path.)

Then call the function write_csv() and pass it the path of the file to be created as well as the variable that holds the EGF geometry.

out_file = "folder/MyShape.csv"

owlet.write_csv(out_file, my_shape)

The resulting CSV file will match the table below:

Park Name	City	Pond	Fountain	GEOMETRY_PT
Post office Square	Boston	FALSE	TRUE	[-71.055631, 42.356243, 2.0]
Boston Common	Boston	TRUE	TRUE	[-71.066412, 42.355465, 10.0]

When saved as a CSV file and opened with an appropriate program, the data can be filtered, new attributes can be added, and existing attributes can be edited.

For example, a State attribute could be added to each record of the table.

Park Name	City	State	Pond	Fountain	GEOMETRY_PT
Post office Square	Boston	MA	FALSE	TRUE	[-71.055631, 42.356243, 2.0]
Boston Common	Boston	MA	TRUE	TRUE	[-71.066412, 42.355465, 10.0]

As long as the GEOMETRY_PT column is not manipulated, the CSV file can be loaded back in to Owlet.

Loading CSV into Owlet

in_file = "path/to/file/MyShape.csv"

my_shape = owlet.read_csv(in_file)

To see that the changes made to the table have been reflected in Owlet, use the print() function.

print(my_shape)

Which will print out:

'PT' GCA object containing 2 feature(s) with the following attributes: ['Park Name', 'City', 'State', 'Pond', 'Fountain']

The above line reveals that my_shape is a PT (Point) file that contains 2 features that each have Park Name, City, State, Pond, and Fountain as attributes. "GCA object" refers to the internal format that Owlet uses to store geometry.

Reading an EGF file and Writing it to a CSV File - Complete Script

import owlet

in_file = "path/to/file/BostonParks.egf"
out_file = "folder/MyShape.csv"

my_shape = owlet.read_egf(in_file)

owlet.write_csv(out_file, my_shape)

Google Earth KML

Owlet can also write KML files for use with Google Earth. Owlet leverages the KML format's "ExtendedData" feature which makes Owlet's KMLs import cleanly into QGIS.

The write_kml() function takes multiple arguments:

1. Path of file to write
2. EGF to write (the variable that an EGF file is saved to)
3. Title of the attribute column that contains the attributes that the features should be named with
4. Name of folder within KML file that will contain the features of the EGF file
5. Folder description (optional)
6. Altitude mode (optional)

Optional arguments do not need to be defined in order for a KML to be produced.

Owlet accepts three types of altitude modes:

• 'ctg' short for Clamped to Ground. Elevation values are ignored and all features are displayed at ground level.
• 'rtg' short for Relative to Ground. Elevation values are rendered as "x" meters above the ground below.
• 'abs' short for Absolute. Elevation values are rendered as "x" meters above mean sea level.

The default altitude mode is ctg

Write a KML file by only providing the required arguments

out_file = "folder/MyShape.kml"

owlet.write_kml(out_file, my_shape, 'Park Name', 'Parks')

Adding a Folder Description

out_file = "folder/MyShape.kml"

owlet.write_kml(out_file, my_shape, 'Park Name', 'Parks', 'Parks near Downtown Boston')

Changing the Altitude Mode

out_file = "folder/MyShape.kml"

owlet.write_kml(out_file, my_shape, 'Park Name', 'Parks', altitude_mode='rtg')

Providing all KML Arguments

out_file = "folder/MyShape.kml"

owlet.write_kml(out_file, my_shape, 'Park Name', 'Parks', 'Parks near Downtown Boston', 'rtg')

Reading an EGF file and Writing it to a KML File - Complete Script

import owlet

in_file = "path/to/file/BostonParks.egf"
out_file = "folder/MyShape.kml"

my_shape = owlet.read_egf(in_file)

owlet.write_kml(out_file, my_shape, 'Park Name', 'Parks', 'Parks near Downtown Boston', 'rtg')

EGF

Owlet will also export to EGF.

out_file = "folder/MyShape.egf"

owlet.write_egf(out_file, my_shape)

   

Owlet License: GNU GPLv3