Vesuvius_SRTM3.png
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Summary
Description Vesuvius SRTM3.png |
English:
Shaded terrain map of the Naples and Mount Vesuvius region from
SRTM
3 elevation data. Each pixel corresponds to about 70x70 m. SRTM tile used was
http://dds.cr.usgs.gov/srtm/version2_1/SRTM3/Eurasia/N40E014.hgt.zip
. The top of the image is 41°N, the left side is 14°E.
|
Date | |
Source | Own work |
Author |
Morn the Gorn
compass rose from Maps_template-fr.svg : Eric Gaba ( Sting - fr:Sting ) |
Other versions |
Derivative works of this file: This file was derived from: Vesuvius SRTM3.xcf |
Code
SRTM data was plotted with the following Python 2 script (requires Python Imaging Library and NumPy ) and then rescaled in Gimp to correct for the raw data aspect ratio at that latitude (about 92 m x 70 m). Terrain shading and hypsometric colors were combined in Gimp in layer multiply mode.
# Read SRTM3 file and create shaded relief
# 2010-04-05
from struct import unpack,calcsize
from numpy import *
import numpy as np
from PIL import Image
row_length = 1201 # row_length is 1201 for SRTM3 or 3601 for SRTM1
file_name = "N40E014.hgt" # from http://dds.cr.usgs.gov/srtm/version2_1/SRTM3/Eurasia/
hlim = 800 # height limit for map [m]
ref_lat = 40.55 # reference latitude
earth_eq = 6371. * 1000. * 2. * pi
x_scale = 1./360.*earth_eq*cos(ref_lat/180.*pi)/row_length
y_scale = 1./360.*earth_eq/row_length
print "1 pixel = %u * %u m" % (x_scale, y_scale)
print "factor", y_scale/x_scale
h = zeros((row_length, row_length))
f = open(file_name, 'r')
li = []
for j in range(row_length):
for i in range(row_length):
d = f.read(2)
(height,) = unpack('>h', d)
h[i,j] = height
if height < -1000:
li.append((i,j))
hmax = h.max()
h3 = zeros_like(h)
h3[:,:] = h[:,:]
print len(li), "missing data points"
def get_nei(z):
h2 = h[z[0]-1:z[0]+2,z[1]-1:z[1]+2]
nn = sum(where(h2 < -1000, 0, 1))
av = sum(where(h2 > -1000, h2, 0)) / float(nn)
return nn, av
# fill missing points with a nearest-neighbor averaging method:
loop = len(li)
lim = 7
while loop > 0:
sd = False
for q in range(len(li)):
if h[li[q]] > -1000.: continue
n, a = get_nei(li[q])
if n >= lim:
print li[q],loop, n, a, lim
h3[li[q]] = a
loop -= 1
sd = True
if not sd: lim -= 1
h[:,:] = h3[:,:]
print "missing points done"
def hext(a):
"Hex color to triplet."
r,g,b = a[0:2], a[2:4], a[4:6]
return int(r, 16), int(g, 16), int(b, 16)
# from http://en.wikipedia.org/wiki/Wikipedia:WikiProject_Maps/Conventions/Topographic_maps:
col_sea = hext("0978ab")
cols = """
{{Mapcolor|r=245|v=244|b=242|hex=#F5F4F2|col=black}}
{{Mapcolor|r=224|v=222|b=216|hex=#E0DED8|col=black}}
{{Mapcolor|r=202|v=195|b=184|hex=#CAC3B8|col=black}}
{{Mapcolor|r=186|v=174|b=154|hex=#BAAE9A|col=black}}
{{Mapcolor|r=172|v=154|b=124|hex=#AC9A7C|col=black}}
{{Mapcolor|r=170|v=135|b=83|hex=#AA8753|col=black}}
{{Mapcolor|r=185|v=152|b=90|hex=#B9985A|col=black}}
{{Mapcolor|r=195|v=167|b=107|hex=#C3A76B|col=black}}
{{Mapcolor|r=202|v=185|b=130|hex=#CAB982|col=black}}
{{Mapcolor|r=211|v=202|b=157|hex=#D3CA9D|col=black}}
{{Mapcolor|r=222|v=214|b=163|hex=#DED6A3|col=black}}
{{Mapcolor|r=232|v=225|b=182|hex=#E8E1B6|col=black}}
{{Mapcolor|r=239|v=235|b=192|hex=#EFEBC0|col=black}}
{{Mapcolor|r=225|v=228|b=181|hex=#E1E4B5|col=black}}
{{Mapcolor|r=209|v=215|b=171|hex=#D1D7AB|col=black}}
{{Mapcolor|r=189|v=204|b=150|hex=#BDCC96|col=black}}
{{Mapcolor|r=168|v=198|b=143|hex=#A8C68F|col=black}}
{{Mapcolor|r=148|v=191|b=139|hex=#94BF8B|col=black}}
{{Mapcolor|r=172|v=208|b=165|hex=#ACD0A5|col=black}}
"""
col = []
for l in cols.splitlines():
if len(l) < 10: continue
i = l.find('#')
if i > -1:
col.append(hext(l[i+1:i+7]))
col.reverse() # -> bottom to top
o = Image.new('RGB', h.shape)
def interp(c, f):
"Interpolate into color table."
r = int((1.-f) * col[c][0] + f * col[c+1][0])
g = int((1.-f) * col[c][1] + f * col[c+1][1])
b = int((1.-f) * col[c][2] + f * col[c+1][2])
return r,g,b
for j in range(row_length):
for i in range(row_length):
c, f = divmod(h[j,i] / hmax * (len(col)-1), 1)
if 0 < h[j,i] < hmax:
o.putpixel((j,i), interp(int(c), f))
elif h[i,j] == hmax:
o.putpixel((j,i), col[-1])
else: o.putpixel((j,i), col_sea)
o.save("map_height.png") # save height map
o2 = o.crop((0,0,942,603))
o2.save("map_height_cropped.png")
# taken from hillshade.py:
#def illumination(idata,azdeg=315.0,altdeg=45.):
def illumination(idata,azdeg=225.0,altdeg=45.):
# convert alt, az to radians
az = azdeg*np.pi/180.0
alt = altdeg*np.pi/180.0
# gradient in x and y directions
dx, dy = np.gradient(idata)
slope = 0.5*np.pi - np.arctan(np.hypot(dx, dy))
aspect = np.arctan2(dx, dy)
odata = np.sin(alt)*np.sin(slope) + np.cos(alt)*np.cos(slope)*np.cos(-az -\
aspect - 0.5*np.pi)
# rescale to interval -1,1
# 1 means maximum sun exposure and 0 means complete shade.
odata = (odata - odata.min())/(odata.max() - odata.min())
return odata
il = 255 * illumination(h)
o4 = Image.new('RGBA', il.shape)
for j in range(row_length-1):
for i in range(row_length-1):
v = int(il[j,i])
if 0 <= v < 128:
alpha = (255 - 2*v)
o4.putpixel((j,i), (0,0,0,alpha))
elif v == 128:
o4.putpixel((j,i), (0,0,0,0))
elif 128 < v < 256:
alpha = 2*(v-128)
o4.putpixel((j,i), (255,255,255,alpha))
else:
o4.putpixel((j,i), (255,255,255,0))
o4.save("il_NW_alpha.png") # NW-illuminated (alpha transparency for use with Inkscape)
Licensing
I, the copyright holder of this work, hereby publish it under the following licenses:
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Creative Commons
Attribution-Share Alike 3.0 Unported
license.
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Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License , Version 1.2 or any later version published by the Free Software Foundation ; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled GNU Free Documentation License . http://www.gnu.org/copyleft/fdl.html GFDL GNU Free Documentation License true true |
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Annotations
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This image is annotated: View the annotations at Commons |