GDAL GetGeoTransform Documentation — Is there an oversight, or what am I misunderstanding?
The documentation for GDALDataset::GetGeoTransform says some things that are rather confusing.
Fetches the coefficients for transforming between pixel/line (P,L) raster space, and projection coordinates (Xp,Yp) space.
Xp = padfTransform[0] + P*padfTransform[1] + L*padfTransform[2];
Yp = padfTransform[3] + P*padfTransform[4] + L*padfTransform[5];
In a north up image,
padfTransform[1]is the pixel width, andpadfTransform[5]is the pixel height.
The upper left corner of the upper left pixel is at position (
padfTransform[0],padfTransform[3]).
The default transform is
(0,1,0,0,0,1)and should be returned even when a CE_Failure error is returned, such as for formats that don't support transformation to projection coordinates.
If this is a matrix, it makes sense that Pixel_X is at 1,1 and Pixel_Y is at 2,2.
Here is my question:
So should the equation for Yp be:
Yp = padfTransform[3] + L*padfTransform[4] + P*padfTransform[5];
in which the positions of L and P are swapped?
Or if I am confused about something, can someone help me get unconfused?
gdal documentation
edited 2 hours ago
user2856
30.1k258105
asked 3 hours ago
philologonphilologon
1205
add a comment |
The documentation for GDALDataset::GetGeoTransform says some things that are rather confusing.
Fetches the coefficients for transforming between pixel/line (P,L) raster space, and projection coordinates (Xp,Yp) space.
Xp = padfTransform[0] + P*padfTransform[1] + L*padfTransform[2];
Yp = padfTransform[3] + P*padfTransform[4] + L*padfTransform[5];
In a north up image,
padfTransform[1]is the pixel width, andpadfTransform[5]is the pixel height.
The upper left corner of the upper left pixel is at position (
padfTransform[0],padfTransform[3]).
The default transform is
(0,1,0,0,0,1)and should be returned even when a CE_Failure error is returned, such as for formats that don't support transformation to projection coordinates.
If this is a matrix, it makes sense that Pixel_X is at 1,1 and Pixel_Y is at 2,2.
Here is my question:
So should the equation for Yp be:
Yp = padfTransform[3] + L*padfTransform[4] + P*padfTransform[5];
in which the positions of L and P are swapped?
Or if I am confused about something, can someone help me get unconfused?
gdal documentation
edited 2 hours ago
user2856
30.1k258105
asked 3 hours ago
philologonphilologon
1205
add a comment |
The documentation for GDALDataset::GetGeoTransform says some things that are rather confusing.
Fetches the coefficients for transforming between pixel/line (P,L) raster space, and projection coordinates (Xp,Yp) space.
Xp = padfTransform[0] + P*padfTransform[1] + L*padfTransform[2];
Yp = padfTransform[3] + P*padfTransform[4] + L*padfTransform[5];
In a north up image,
padfTransform[1]is the pixel width, andpadfTransform[5]is the pixel height.
The upper left corner of the upper left pixel is at position (
padfTransform[0],padfTransform[3]).
The default transform is
(0,1,0,0,0,1)and should be returned even when a CE_Failure error is returned, such as for formats that don't support transformation to projection coordinates.
If this is a matrix, it makes sense that Pixel_X is at 1,1 and Pixel_Y is at 2,2.
Here is my question:
So should the equation for Yp be:
Yp = padfTransform[3] + L*padfTransform[4] + P*padfTransform[5];
in which the positions of L and P are swapped?
Or if I am confused about something, can someone help me get unconfused?
gdal documentation
edited 2 hours ago
user2856
30.1k258105
asked 3 hours ago
philologonphilologon
1205
The documentation for GDALDataset::GetGeoTransform says some things that are rather confusing.
Fetches the coefficients for transforming between pixel/line (P,L) raster space, and projection coordinates (Xp,Yp) space.
Xp = padfTransform[0] + P*padfTransform[1] + L*padfTransform[2];
Yp = padfTransform[3] + P*padfTransform[4] + L*padfTransform[5];
In a north up image,
padfTransform[1]is the pixel width, andpadfTransform[5]is the pixel height.
The upper left corner of the upper left pixel is at position (
padfTransform[0],padfTransform[3]).
The default transform is
(0,1,0,0,0,1)and should be returned even when a CE_Failure error is returned, such as for formats that don't support transformation to projection coordinates.
If this is a matrix, it makes sense that Pixel_X is at 1,1 and Pixel_Y is at 2,2.
Here is my question:
So should the equation for Yp be:
Yp = padfTransform[3] + L*padfTransform[4] + P*padfTransform[5];
in which the positions of L and P are swapped?
Or if I am confused about something, can someone help me get unconfused?
gdal documentation
gdal documentation
edited 2 hours ago
user2856
30.1k258105
asked 3 hours ago
philologonphilologon
1205
edited 2 hours ago
user2856
30.1k258105
asked 3 hours ago
philologonphilologon
1205
edited 2 hours ago
user2856
30.1k258105
edited 2 hours ago
user2856
30.1k258105
edited 2 hours ago
user2856
30.1k258105
30.1k258105
asked 3 hours ago
philologonphilologon
1205
asked 3 hours ago
philologonphilologon
1205
asked 3 hours ago
philologonphilologon
1205
1205
add a comment |
add a comment |
1 Answer
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No.
For a north up image with no rotation (i.e. padfTransform[4] == padfTransform[2] == 0), the formula simply becomes:
Xp = padfTransform[0] + P*padfTransform[1];
Yp = padfTransform[3] + L*padfTransform[5];
# Where P = column number and L = row number
i.e add the starting X (or Y) to the column (or row) number multiplied by the pixel width (or height).
The rotation terms may be what's tripping you up...? When a pixel is rotated, the Y skew needs to be considered when calculating the X map coordinate and the X skew needs to be considered when calculating the Y map coordinate. There's a quite detailed explanation in the wikipedia article on world files.
answered 2 hours ago
user2856user2856
30.1k258105
That there is rotation is what was tripping me up. So can you tell me what P and L stand for? I naively supposed that P was Pixel dimension and L was Line dimension (the lines between pixels). Yes, that is as foolish as a sophomore reasoning with senior. In that vein, what do those letters stand for?
– philologon
2 hours ago
1
@philologon P is column number, and L is row number. These are "coordinates" on the raster image.
– Mike T
2 hours ago
Thanks. I now see it is right there in the documentation. I always find a way to embarrass myself in these kinds of things, usually by skimming too fast.
– philologon
2 hours ago
add a comment |
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1 Answer
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1 Answer
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votes
No.
For a north up image with no rotation (i.e. padfTransform[4] == padfTransform[2] == 0), the formula simply becomes:
Xp = padfTransform[0] + P*padfTransform[1];
Yp = padfTransform[3] + L*padfTransform[5];
# Where P = column number and L = row number
i.e add the starting X (or Y) to the column (or row) number multiplied by the pixel width (or height).
The rotation terms may be what's tripping you up...? When a pixel is rotated, the Y skew needs to be considered when calculating the X map coordinate and the X skew needs to be considered when calculating the Y map coordinate. There's a quite detailed explanation in the wikipedia article on world files.
answered 2 hours ago
user2856user2856
30.1k258105
That there is rotation is what was tripping me up. So can you tell me what P and L stand for? I naively supposed that P was Pixel dimension and L was Line dimension (the lines between pixels). Yes, that is as foolish as a sophomore reasoning with senior. In that vein, what do those letters stand for?
– philologon
2 hours ago
1
@philologon P is column number, and L is row number. These are "coordinates" on the raster image.
– Mike T
2 hours ago
Thanks. I now see it is right there in the documentation. I always find a way to embarrass myself in these kinds of things, usually by skimming too fast.
– philologon
2 hours ago
add a comment |
No.
For a north up image with no rotation (i.e. padfTransform[4] == padfTransform[2] == 0), the formula simply becomes:
Xp = padfTransform[0] + P*padfTransform[1];
Yp = padfTransform[3] + L*padfTransform[5];
# Where P = column number and L = row number
i.e add the starting X (or Y) to the column (or row) number multiplied by the pixel width (or height).
The rotation terms may be what's tripping you up...? When a pixel is rotated, the Y skew needs to be considered when calculating the X map coordinate and the X skew needs to be considered when calculating the Y map coordinate. There's a quite detailed explanation in the wikipedia article on world files.
answered 2 hours ago
user2856user2856
30.1k258105
That there is rotation is what was tripping me up. So can you tell me what P and L stand for? I naively supposed that P was Pixel dimension and L was Line dimension (the lines between pixels). Yes, that is as foolish as a sophomore reasoning with senior. In that vein, what do those letters stand for?
– philologon
2 hours ago
1
@philologon P is column number, and L is row number. These are "coordinates" on the raster image.
– Mike T
2 hours ago
Thanks. I now see it is right there in the documentation. I always find a way to embarrass myself in these kinds of things, usually by skimming too fast.
– philologon
2 hours ago
add a comment |
No.
For a north up image with no rotation (i.e. padfTransform[4] == padfTransform[2] == 0), the formula simply becomes:
Xp = padfTransform[0] + P*padfTransform[1];
Yp = padfTransform[3] + L*padfTransform[5];
# Where P = column number and L = row number
i.e add the starting X (or Y) to the column (or row) number multiplied by the pixel width (or height).
The rotation terms may be what's tripping you up...? When a pixel is rotated, the Y skew needs to be considered when calculating the X map coordinate and the X skew needs to be considered when calculating the Y map coordinate. There's a quite detailed explanation in the wikipedia article on world files.
answered 2 hours ago
user2856user2856
30.1k258105
No.
For a north up image with no rotation (i.e. padfTransform[4] == padfTransform[2] == 0), the formula simply becomes:
Xp = padfTransform[0] + P*padfTransform[1];
Yp = padfTransform[3] + L*padfTransform[5];
# Where P = column number and L = row number
i.e add the starting X (or Y) to the column (or row) number multiplied by the pixel width (or height).
The rotation terms may be what's tripping you up...? When a pixel is rotated, the Y skew needs to be considered when calculating the X map coordinate and the X skew needs to be considered when calculating the Y map coordinate. There's a quite detailed explanation in the wikipedia article on world files.
answered 2 hours ago
user2856user2856
30.1k258105
edited 1 hour ago
answered 2 hours ago
user2856user2856
30.1k258105
answered 2 hours ago
user2856user2856
30.1k258105
answered 2 hours ago
user2856user2856
30.1k258105
30.1k258105
That there is rotation is what was tripping me up. So can you tell me what P and L stand for? I naively supposed that P was Pixel dimension and L was Line dimension (the lines between pixels). Yes, that is as foolish as a sophomore reasoning with senior. In that vein, what do those letters stand for?
– philologon
2 hours ago
1
@philologon P is column number, and L is row number. These are "coordinates" on the raster image.
– Mike T
2 hours ago
Thanks. I now see it is right there in the documentation. I always find a way to embarrass myself in these kinds of things, usually by skimming too fast.
– philologon
2 hours ago
add a comment |
That there is rotation is what was tripping me up. So can you tell me what P and L stand for? I naively supposed that P was Pixel dimension and L was Line dimension (the lines between pixels). Yes, that is as foolish as a sophomore reasoning with senior. In that vein, what do those letters stand for?
– philologon
2 hours ago
1
@philologon P is column number, and L is row number. These are "coordinates" on the raster image.
– Mike T
2 hours ago
Thanks. I now see it is right there in the documentation. I always find a way to embarrass myself in these kinds of things, usually by skimming too fast.
– philologon
2 hours ago
That there is rotation is what was tripping me up. So can you tell me what P and L stand for? I naively supposed that P was Pixel dimension and L was Line dimension (the lines between pixels). Yes, that is as foolish as a sophomore reasoning with senior. In that vein, what do those letters stand for?
– philologon
2 hours ago
That there is rotation is what was tripping me up. So can you tell me what P and L stand for? I naively supposed that P was Pixel dimension and L was Line dimension (the lines between pixels). Yes, that is as foolish as a sophomore reasoning with senior. In that vein, what do those letters stand for?
– philologon
2 hours ago
1
1
@philologon P is column number, and L is row number. These are "coordinates" on the raster image.
– Mike T
2 hours ago
@philologon P is column number, and L is row number. These are "coordinates" on the raster image.
– Mike T
2 hours ago
Thanks. I now see it is right there in the documentation. I always find a way to embarrass myself in these kinds of things, usually by skimming too fast.
– philologon
2 hours ago
Thanks. I now see it is right there in the documentation. I always find a way to embarrass myself in these kinds of things, usually by skimming too fast.
– philologon
2 hours ago
add a comment |
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