[英]Geopandas + rasterio : isolate a vector as png
我正在嘗試將城市的邊界隔離為 png 的單個部分。 我的目標是將這個 png 疊加到非常古老的衛星照片上。
為此,我收集了一個復制照片尺寸的光柵文件和一個帶邊界的矢量文件。 然后,我使用了光柵:
import rasterio
from rasterio.plot import show
src = rasterio.open("my_raster.tiff")
和 geopandas 的等價物:
import geopandas as gpd
GDF = gpd.read_file("boundary.shp")
我檢查了 src 和 GDF 之間的坐標參考系是否完全相同,然后我使用 matplotlib 正確放置邊界:
import matplotlib.pyplot as plt
fig, ax = plt.subplots(figsize=(20, 10))
show(src.read(), transform=src.transform, ax=ax)
GDF.plot(ax=ax, color='white')
plt.show()
這表明:
效果很好,但我不能用 savefig() 只保存 png 中的邊界。 我試圖將 ax 分開,用 ax1 表示光柵,用 ax2 表示矢量,但它沒有用......
我可以只保存圖的這一部分嗎?
好的,經過一番搜索,我保存了我的 plot 如下:
import matplotlib.pyplot as plt
fig, ax = plt.subplots(figsize=(20, 10))
show(src.read(), transform=src.transform, ax=ax)
GDF.plot(ax=ax, color='#fff')
ax.set_axis_off()
fig.savefig("test.png", dpi=220, bbox_inches = 'tight')
plt.show()
然后,我在一點 function 中使用了 PIL:
from PIL import ImageTk, Image
def only_boundary(image):
# first, convert picture as RGBA
with Image.open(image).convert("RGBA") as img:
pixels = img.load()
for i in range(img.size[0]):
for j in range(img.size[1]):
# if a pixel is not white...
if pixels[i,j] != (255, 255, 255,255):
#it becomes transparent
pixels[i,j] = (0, 0, 0, 0)
# then the loops are over, we save
im = img.save(image)
only_boundary("test.png") 保存了好結果!
我們可以通過使用 OpenCV 輪廓使方法更清晰。
myfilter='example'
myfilter_raster=os.path.join(raster_path,myfilter+'.tif')
with rasterio.open(myfilter_raster) as src:
vector_df=gdf_rbb[gdf_rbb.idarpt==myfilter].copy()
out_image, out_transform = rasterio.mask.mask(src, vector_df.geometry.to_list(), crop=False)
out_meta = src.meta
out_meta.update({"driver": "PNG",
"height": out_image.shape[1],
"width": out_image.shape[2],
"transform": out_transform})
out_file=myfilter+'.png'
out_file=os.path.join(mask_images_path,out_file)
print('Generated' ,out_file)
mask = out_image[0].astype("uint8")
mask[mask > 0] = 255
border = cv2.copyMakeBorder(mask, 1, 1, 1, 1, cv2.BORDER_CONSTANT, value=0 )
contours, hierarchy = cv2.findContours(border, cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE, offset=(-1, -1))
boundary_image=np.zeros(mask.shape)
for contour in contours:
cv2.drawContours(boundary_image,[contour],0,(255,255,255),3)
plt.imshow(boundary_image)
plt.show()
with rasterio.open(out_file, 'w', **out_meta) as dst:
dst.write(boundary_image , 1)
# from rasterio.plot import show
# fig, ax = plt.subplots(figsize=(20, 10))
# show(src.read(), transform=src.transform, ax=ax)
# vector_df.plot(ax=ax, color='white')
# plt.show()
使用 opencv 邊緣檢測的另一種簡單方法。
myfilter='example'
myfilter_raster=os.path.join(raster_path,myfilter+'.tif')
with rasterio.open(myfilter_raster) as src:
vector_df=gdf_rbb[gdf_rbb.idarpt==myfilter].copy()
out_image, out_transform = rasterio.mask.mask(src, vector_df.geometry.to_list(), crop=False)
out_meta = src.meta
out_meta.update({"driver": "PNG",
"height": out_image.shape[1],
"width": out_image.shape[2],
"transform": out_transform})
out_file=myfilter+'2.png'
out_file=os.path.join(mask_images_path,out_file)
print('Generated' ,out_file)
mask = out_image[0].astype("uint8")
mask[mask > 0] = 255
edges = cv2.Canny(mask,100,200)
plt.subplot(121)
plt.axis('off')
plt.imshow(mask,cmap = 'gray')
plt.title('Original Image')
plt.subplot(122),
plt.imshow(edges,cmap = 'gray')
plt.title('Edge Image')
plt.show()
with rasterio.open(out_file, 'w', **out_meta) as dst:
dst.write(edges , 1)
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