geocachinggps
I am not sure if this forum is proper place for that kind of question but i hope to get some advice…
I looking for some scenario (examples, ideas) for urban game (location-based game) with usage of GPS devices. The thing is that the game should touch on spatial planning subject. It will be for teenager audience.
As @Loxodromes said above, I too am not sure that an open source library exists to do this. But it's simple enough to do in Python if you're happy enough with the scripting. For example, if you have access to numpy and scipy you can use a KDTree to easily calculate points from trail A that are within some tolerance of points from trail B.
With a bit of work you can take this a bit further by stacking the points into a single array and playing with labelled groups. This has the bonus of coping with more than two base data sets for comparison, though note this is not memory friendly - if you've got a lot of points you might need to do some work to make this more memory efficient. This also assumes everything is in the same projection.
import numpy as np
import scipy.spatial
For this example I'll dummy up some data, but take a look at numpy.loadtxt to read in your CSVs.
np.random.seed(20140201)
num_pts = 50
points_a = np.vstack([
np.linspace(0., 10., num=num_pts),
np.linspace(10., 0., num=num_pts)
]).T
points_b = points_a + np.random.random([num_pts, 2]) - 0.5
points_c = points_a + np.random.random([num_pts, 2]) - 0.5
points_d = points_a + np.vstack([
np.sin(np.linspace(0., 2 * np.pi, num_pts)),
np.sin(np.linspace(0., 2 * np.pi, num_pts)),
]).T
all_trails = [points_a, points_b, points_c, points_d]
You'll also need to specify a tolerance
tolerance = 0.1
Then, so you can process all the points in bulk but still know what group they're in, stack the arrays.
labelled_pts = np.vstack([
np.hstack([a, np.ones((a.shape[0], 1)) * i])
for i, a in enumerate(all_trails)
])
You can now build a KDTree from the labelled points. Remember that you don't want the labels themselves in the tree - they're used later on to classify results
tree = scipy.spatial.KDTree(labelled_pts[:, :2])
You use the ball point algorithm to get all the points within tolerance of another set of points (which is conveniently also our input points).
points_within_tolerance = tree.query_ball_point(labelled_pts[:, :2], tolerance)
This returns an array of the same length as the incoming points, with each value in the array being a tuple of indexes of the found points in the tree. Because you put in our original set there will always be at least one match. However you can then build a simple vectorisation function to test whether each item in the tree matches a point from a different group.
vfunc = np.vectorize(lambda a: np.any(labelled_pts[a, 2] != labelled_pts[a[0], 2]))
matches = vfunc(points_within_tolerance)
matching_points = labelled_pts[matches, :2]
The vfunc simply returns a numpy array of the results of this function, in this case True or False which we can use to index out our points.
So now you have points on the GPS trails which cross, but you want to group points into contiguous segments of track that overlap. For that you can use the scipy hierarchical clustering methods to group the data into groups which are linked by at most the tolerance distance.
import scipy.cluster.hierarchy
clusters = scipy.cluster.hierarchy.fclusterdata(matching_points, tolerance, 'distance')
clusters is an array of the same length of your matched points containing cluster indexes for each point. This means it's easy to get back a table of x, y, original_trail, segment by stacking the output together.
print np.hstack([
matching_points, #x, y
np.vstack([
labelled_pts[matches, 2], #original_trail
clusters #segment
]).T
])
Or you can draw up the clusters.
from itertools import cycle, izip
import matplotlib.pyplot as plt
for pts, colour in izip(all_trails, cycle(['blue', 'red', 'orange', 'green', 'pink'])):
plt.scatter(pts[:, 0], pts[:, 1], c=colour)
for clust_idx, shape, size in izip(set(clusters), cycle(['o', 'v', '^', '<', '>', 's', 'p', '*', '8', 'd']), cycle([40, 50, 60])):
plt.scatter(matching_points[clusters == clust_idx, 0], matching_points[clusters == clust_idx, 1], c='yellow', marker=shape, s=size)
plt.show()
Hopefully this all makes sense!
Maybe you could use RTKLIB with https://github.com/fcancillo/RXtoRINEX-V2.0 to translate the SIRFstarIV data into RINEX and other formats.
It's been years since you asked, so maybe it would be a good time to look into newer devices, with newer capabilities and power requirements.
Depending on the accuracy you require, you can get pretty low power consumption with the system doing the calculations in-chip. If you need to do the processing off-line, you needs to transfer lots of satellite data to the system that will do the calculations, which might cost power.
uBlox has a NEO-7P or NEO-M8P devices with PPP capable power devices ($200 on a board in 2018) that can calculate cm-scale accurate fixes on-chip, so you may not need an extenal library. They are also compatible with RTKLIB, if you would like to do that.
Best Answer
You might find some ideas at: