Usage¶

To use EVTech in a project:

import evtech

In order to load a dataset (a single collection of images):

# Load the cameras
nadirs, obliques = evtech.load_dataset('/path/to/dataset')

# Get the image data for the first nadir camera as a numpy array
nadir_cam = nadirs[0]
img = nadir_cam.load_image()

The camera object also stores the average elevation of the image and the geographical bounds of the image, which can be retreived as a Shapely polgon:

# Get average elevation for image
elev = nadir_cam.elevation

# Get bounding polygon
bounds = nadir_cam.get_bounds()

# Create geojson from bounds using shapely, json
from shapely.geometry import mapping
import json

geo_json = json.dumps(mapping(bounds))

From here you can also look at operations with the camera, such as projecting a ray from the camera at a given pixel. Also projecting a latitude, longitude, elevation point into the camera to get the pixel location:

image_pt = nadir_cam.project_to_camera(lon, lat, elevation)
ray = nadir_cam.project_from_camera(col, row)

Rays can be used with ground elevation to find the intersection of the pixel and the ground:

ground_point_at_pxiel = ray.intersect_at_elevation(nadir_cam.elevation)

We have provided a simple single-image height measurement function that uses the camera and two points to compute the height of an object at a given elevation:

height = nadir_cam.height_between_points(base_img_pt, peak_image_pt, nadir_cam.elevation)

Lastly, we have proivded a function to take multiple cameras and associated image points, and triangulate a three dimensional point:

# Load cameras from dataset
cam1 = nadirs[0]
cam2 = obliques[1]
cam3 = obliques[2]
cams = [cam1, cam2, cam3]

# Points from images associated with cam1, cam2, cam3
pt1 = [605,171]
pt2 = [304,536]
pt3 = [879,441]
pts = [pt1, pt2, pt3]

world_pt = evtech.triangulate_point_from_cameras(cams, pts)

OpenCV has a number of tools that can be used for image manipulation and display, refer to the imgproc and highgui packages. Note that these are c++ bindings, you can find many examples that may be helpful on how to use the OpenCV Python bindings here:

import cv2

# Get image
img = nadir_cam.load_image()

# Display an image
cv2.namedWindow('image', cv2.WINDOW_NORMAL)
cv2.imshow('image',img)
k = cv2.waitKey(0)

# wait for ESC key to exit
if k == 27:
    cv2.destroyAllWindows()