CODEWITHSUNDEEP
imageplotmatplotlibcartography
heltonbiker
heltonbiker

Reputation: 27615

How to plot geo-referenced image so that it "fits" the plot coordinate system in Matplotlib

A very similar question, solved the same way: how to use 'extent' in matplotlib.pyplot.imshow

I have a list of geographical coordinates (a "tracklog") that describe a geographical trajectory. Also, I have the means of obtaining an image spanning the tracklog coverage, where I know the "geographical coordinates" of the corners of the image.

My plot currently looks like this (notice the ticks - x=longitudes, y=latitudes, in UTM, WGS84):

enter image description here

Then suppose I know the corner coordinates of the following image (or a version of it without the blue track), and would like to plot it SO THAT IT FITS THE COORDINATE SYSTEM of the plot.

enter image description here

How would I do it?

(as a side note, in case that matters, I plan to use tiles)

As per the comment of Joe Kington (waiting for his actual answer so that I can accept it), the following code works as expected, giving a pannable and zoomable fixed-aspect "georeferenced" tile over which I am able to plot tracklogs:

import matplotlib.pyplot as plt
import Image
import numpy

imarray = numpy.asarray(Image.open('map.jpg'))

plt.plot([0,1], [0,1], 'o', c='red', ms=20)  ## some reference circles for debugging
plt.imshow(imarray, extent=[0,1,0,1])   ## some random map whose corners have known coordinates
plt.axis('equal')
plt.show()

enter image description here

Upvotes: 2

Views: 4163

Answers (2)

Moritz Makowski
Moritz Makowski

Reputation: 382

I solved it by taking a screenshot from some maps program and then finding out the lat/lon borders of the image. I can imshow the whole map and the use set_xlim and set_ylim to only show the area I want to.

Since the maps in navigation programs are plot maps in a 1km:1km aspect ratio, you have to manually set that ratio using the sinus of the latitude.

from PIL import Image

munich_map = Image.open("images/munich-map.png")

...

axis.imshow(
   munich_map,
   extent=[11.245921, 11.930659, 47.949627, 48.279644],
   aspect=1 / math.sin(math.radians(48)),
)

axis.set_xlim(from_lon, to_lon)
axis.set_ylim(from_lat, to_lat)

enter image description here

Upvotes: 0

oz123
oz123

Reputation: 28868

There is really not much of an answer here, but if you are using matplotlib, and you geos-tuff, take a look at matplotlib.basemap.
By default all operations are done on UTM maps, but you can choose your own projection. Take also a look on the list of good tutorials in http://www.geophysique.be, for example.

Upvotes: 0

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