File:Vesuvius SRTM3.png
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This is a file from the Wikimedia Commons. The description on its description page there is shown below.
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Summary
DescriptionVesuvius SRTM3.png |
English: Shaded terrain map of the Naples and Mount Vesuvius region from SRTM3 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.
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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:
This file is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.
- You are free:
- to share – to copy, distribute and transmit the work
- to remix – to adapt the work
- Under the following conditions:
- attribution – You must give appropriate credit, provide a link to the license, and indicate if changes were made. You may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use.
- share alike – If you remix, transform, or build upon the material, you must distribute your contributions under the same or compatible license as the original.
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.htmlGFDLGNU Free Documentation Licensetruetrue |
You may select the license of your choice.
Annotations InfoField | This image is annotated: View the annotations at Commons |
Items portrayed in this file
depicts
4 March 2010
image/png
File history
Click on a date/time to view the file as it appeared at that time.
Date/Time | Dimensions | User | Comment | |
---|---|---|---|---|
current | 18:01, 4 April 2010 | 942 × 794 (922 KB) | Morn | corrected color of a lake |
File usage
The following page uses this file:
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