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creare-com / pydem

Python library for Global Hydrology Analysis. Used to calculate upstream contributing area, aspect, slope, and topographic wetness index.
Apache License 2.0
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Working with Nan values #12

Closed kothawadegs closed 6 years ago

kothawadegs commented 7 years ago

I tried pyDEM on SRTM data, I'm able to calculate TWI, but in the final output, I'm getting Nan values as well. Can you please help me how to resolve this issue or is there any pre-processing required? Also can you please add a comment on visualization part of the TWI on the map, like Folium etc?

mpu-creare commented 7 years ago

NaNn values are reasonable since twi = log(uca / slope) and in certain regions the slope is '0' .

Do you get single pixel nan's? or do they come in larger groups? Can you send us a 5x5 grid of elevation, aspect, slope, uca, and twi around one of the single pixel nan's?

Not sure what you're asking about the visualization...

kothawadegs commented 7 years ago

I'm getting ndarray containing TWI values. My question here is how to plot/visualize these values of TWI?

mpu-creare commented 7 years ago

Oh! There are a lot of ways to do so. I personally just use plain old matplotlib:

from matplotlib.pyplot import *
matshow(twi)
show()
kothawadegs commented 7 years ago

Thanks..! What if I want to overlay this information in Folium map to validate the results with the actual geographical feature?

mpu-creare commented 7 years ago

I have not used Folium, so unfortunately I cannot comment on that. I have saved the results to a GeoTIFF and then used QGis to visualize / overlay.

kothawadegs commented 7 years ago

I used matshow to show and saved the output image. It's looking like the image attached here. Is there any way to make it better visualization? srtm1arcbangsouth

mpu-creare commented 7 years ago

I'm not sure what your goal is for your visualization. I suggest looking at matplotlib's documentation, as visualization is not one of pydem's core functions.