Find lat/long coordinates from pixel point in .geotiff using python and gdal

问题

I have points defined by pixel coordinates in a .geotiff imagesat.

I am trying to convert these pixel coordinates into longitude and latitude.

At first a tried to adapt the given code from the inverse question i previously asked here

def pixel_to_world(geo_matrix, x, y):
    ul_x   = geo_matrix[0]
    ul_y   = geo_matrix[3]
    x_dist = geo_matrix[1]
    y_dist = geo_matrix[5]
    _x = x * x_dist + ul_x
    _y = y * y_dist + ul_y
    return (_x, _y)

def build_transform_inverse(dataset, EPSG):
    source = osr.SpatialReference(wkt=dataset.GetProjection())
    target = osr.SpatialReference()
    target.ImportFromEPSG(4326)
    return osr.CoordinateTransformation(source, target)

def find_spatial_coordinate_from_pixel(dataset, transform, x, y):
    point = ogr.Geometry(ogr.wkbPoint)
    point.AddPoint(float(x), float(y))
    point.Transform(transform)
    return pixel_to_world(dataset.GetGeoTransform(), point.GetX(), point.GetY())

ds = gdal.Open(source_directory_path + filename)
_t = build_transform_inverse(ds, 4326)
coordinates = find_spatial_coordinate_from_pixel(ds, _t, point[0], point[1])

But my final coordinates are incorrect, i get something like (-1528281.9351183572, 1065990.778732022) instead of (-13.728790283203121, 9.531686027524676) with

ul_x = -1528281.943533814, 
ul_y = 1065990.7964650677, 
x_dist = 0.5970709765586435, 
y_dist = -0.5972870511184641

I also tried the rasterio approach like :

import rasterio

with rasterio.open('path/to/file.tiff') as map_layer:
    pixels2coords = map_layer.xy(2679,2157)
    print(pixels2coords)

Witch fails to return a proper long lat coordinate couple ( it returns (-1526993.7629018887, 1064390.365811596) ).

What am i doing wrong ?

回答1:

You have flipped the order in which you convert between pixels, projected coordinates and lat longs. You are doing the order pixels -> lat lngs -> projected it should be pixels -> projected -> lat lngs.

The following should work

from osgeo import osr, ogr, gdal


def pixel_to_world(geo_matrix, x, y):
    ul_x = geo_matrix[0]
    ul_y = geo_matrix[3]
    x_dist = geo_matrix[1]
    y_dist = geo_matrix[5]
    _x = x * x_dist + ul_x
    _y = y * y_dist + ul_y
    return _x, _y


def build_transform_inverse(dataset, EPSG):
    source = osr.SpatialReference(wkt=dataset.GetProjection())
    target = osr.SpatialReference()
    target.ImportFromEPSG(EPSG)
    return osr.CoordinateTransformation(source, target)


def find_spatial_coordinate_from_pixel(dataset, transform, x, y):
    world_x, world_y = pixel_to_world(dataset.GetGeoTransform(), x, y)
    point = ogr.Geometry(ogr.wkbPoint)
    point.AddPoint(world_x, world_y)
    point.Transform(transform)
    return point.GetX(), point.GetY()

ds = gdal.Open(source_directory_path + filename)
_t = build_transform_inverse(ds, 4326)
coordinates = find_spatial_coordinate_from_pixel(ds, _t, point[0], point[1])
print(coordinates)

In find_spatial_coordinate_from_pixel i have flipped the order, such that pixel_to_world is now called first, before the coordinate transformation.

来源：https://stackoverflow.com/questions/59052516/find-lat-long-coordinates-from-pixel-point-in-geotiff-using-python-and-gdal

标签

python

gdal

ogr

rasterio