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Wrap GMT's standard data type GMT_GRID for grids #2398
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pygmt/datatypes.py
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pad = header.pad[:] | ||
x = self.x[: header.n_columns] | ||
y = self.y[: header.n_rows] | ||
data = np.array(self.data[: header.mx * header.my]).reshape( |
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The grid has n_columns
columns and n_rows
rows, but usually the number of data points in memory are not n_columns * n_rows
due to grid pads. For some specific reasons, GMT usually adds two more rows/columns on west, east, south, north sides. So, we should have:
mx = pad[0] + n_columns + pad[1]
my = pad[2] + n_rows + pad[3]
That's why we need to use the following codes to get the data matrix:
data = np.array(self.data[: header.mx * header.my]).reshape(
(header.my, header.mx)
)[pad[2] : header.my - pad[3], pad[0] : header.mx - pad[1]]
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This is amazing, thanks for pulling this together @seisman! I'll need to take a closer look to review this properly, but it's looking very promising 🤩
Currently the unit tests are failing, mostly because the output xarray.DataArray
doesn't have the same attributes/metadata as when we were using the NetCDF tempfile. Will need to find a way to copy those metadata over somehow.
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Most of the tests on grdview
(which uses grdcut
for the fixture) are failing with an incorrect figure size. Is there something to be fixed with the padding?
No, if you compare the baseline and result images, you'll see that the differences are caused by the |
Added a temporary workaround at 6280e39. And now all tests pass except |
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CodSpeed Performance ReportMerging #2398 will improve performances by ×2Falling back to comparing Summary
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I think this PR is now ready for review. Generally speaking, this PR does three things:
I think it makes more sense to split this big PR into three smaller PRs. Maybe after this PR is reviewed and approved. |
@@ -1946,6 +1951,70 @@ def virtualfile_to_dataset( | |||
return result.to_numpy() | |||
return result # pandas.DataFrame output | |||
|
|||
def virtualfile_to_raster( |
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In this method, kind
can be grid
, cube
, image
or None
. If None
, we will call Session.inquire_virtualfile
to determine the family of the virtualfile.
Most GMT modules can write grids only, so we can set kind="grid"
to avoid calling Session.inquire_virtualfile
.
Here are some exceptions:
grdmix
writes imagesgrdcut
writes grids or imagesgrdimage -A
writes images [Unimplemented in PyGMT]greenspine
writes grids or cubesgrdinterpolate
writes grids or cubes
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Most GMT modules can write grids only, so we can set
kind="grid"
to avoid callingSession.inquire_virtualfile
.
Yes, I think we can set kind="grid"
, unless we know if GMT will allow passing GMT_IMAGE to certain grd* modules in the future. For example, maybe grdclip
would allow GMT_IMAGE inputs at some point, and so we might want to set kind=None
for future-proofing.
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We need to do more refactoring if grdclip
would support GMT_IMAGE in the future, since we need to check the kind of the input data (grid in, grid out or image in, image out), similar to what we have to do to grdcut
(xref: #2398 (comment)).
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Ok, I meant if upstream GMT were to support passing GMT_IMAGE
into grdclip
in the future, but not sure when that would happen. Ok to just default to kind='grid'
for now, since that's the current behaviour I think.
Can probably keep it as one PR, I think you've done a good job of cherrypicking the GMT grid header and inquire virtualfile stuff out already, and the code here is reasonable to review. I'll give this a proper final review after Thursday-ish as I'm attending the MIGARS conference this week (have already received thanks from a couple of PyGMT users here, so I'll pass that on 😃). |
Co-authored-by: Yvonne Fröhlich <[email protected]>
# Flip the coordinates and data if necessary so that coordinates are ascending. | ||
# `grid.sortby(list(grid.dims))` sometimes causes crashes. | ||
# The solution comes from https://github.com/pydata/xarray/discussions/6695. | ||
for dim in grid.dims: | ||
if grid[dim][0] > grid[dim][1]: | ||
grid = grid.isel({dim: slice(None, None, -1)}) |
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Could you elaborate a bit on this part? Sort ascending is probably needed for the x (longitude) dimension. But for the y (latitude) dimension, it is quite common to sort in descending order (y going from North Pole +90 to South Pole -90). What is the typical sorting order returned from GMT?
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I think GMT requires ascending order for longitude/latitude. Similar codes are already used at (The codes below use sortby
, but we can't use it here due to a mysterious reason (xref #2398 (comment)).)
pygmt/pygmt/clib/conversion.py
Lines 122 to 124 in 70d666e
if any(i < 0 for i in inc): # Sort grid when there are negative increments | |
inc = [abs(i) for i in inc] | |
grid = grid.sortby(variables=list(grid.dims), ascending=True) |
I tried to find some evidence from the GMT source codes but failed because the codes are so complicated. Perhaps the most straightforward evidence is from following lines (https://github.com/GenericMappingTools/gmt/blob/e493ccc220d9e997abb655cb461142ed2e7cc777/src/gmt_nc.c#L754):
/* Determine grid step */
header->inc[GMT_X] = gmt_M_get_inc (GMT, dummy[0], dummy[1], header->n_columns, registration);
if (gmt_M_is_dnan(header->inc[GMT_X]) || gmt_M_is_zero (header->inc[GMT_X])) header->inc[GMT_X] = 1.0;
if (header->n_columns == 1) registration = GMT_GRID_PIXEL_REG; /* The only way to have a grid like that */
/* Extend x boundaries by half if we found pixel registration */
if (registration == GMT_GRID_NODE_REG && header->registration == GMT_GRID_PIXEL_REG)
header->wesn[XLO] = dummy[0] - header->inc[GMT_X] / 2.0,
header->wesn[XHI] = dummy[1] + header->inc[GMT_X] / 2.0;
else /* Use as is */
header->wesn[XLO] = dummy[0], header->wesn[XHI] = dummy[1];
in which dummy[0]
and dummy[1]
is the min/max value of the x vector. For pixel registration, GMT extends the x boundaries by half a grid. The codes only make sense when head->inc[GMT_X]
is positive.
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Ok, from what I can tell, this means GMT expects grids with coordinates sorted in ascending order. But here in the to_dataarray()
method, we're going from GMT virtualfile to xarray.DataArray
, so is this sorting still needed or can we return the grid as is? Maybe the sort ascending logic is only needed in virtualfile_from_grid
(which is implemented in the dataarray_to_matrix
conversion function already)?
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But here in the
to_dataarray()
method, we're going from GMT virtualfile toxarray.DataArray
, so is this sorting still needed or can we return the grid as is? Maybe the sort ascending logic is only needed invirtualfile_from_grid
(which is implemented in thedataarray_to_matrix
conversion function already)?
Hmmm, your comments make more sense. I tried to remove these sorting codes locally. Here is the output:
In [1]: import xarray as xr
In [2]: from pygmt import which
In [3]: path = which("@earth_relief_01d_g", download="a")
In [4]: grid1 = xr.load_dataarray(path)
In [6]: from pygmt.clib import Session
...: with Session() as lib:
...: with lib.virtualfile_out(kind="grid") as voutgrd:
...: lib.call_module("read", f"{path} {voutgrd} -Tg")
...: grid = lib.read_virtualfile(voutgrd, kind="grid")
...: grid2 = grid.contents.to_dataarray()
...:
In [7]: grid1
Out[7]:
<xarray.DataArray 'z' (lat: 181, lon: 361)> Size: 523kB
array([[ 2865. , 2865. , 2865. , ..., 2865. , 2865. , 2865. ],
[ 3088. , 3087.5, 3087. , ..., 3088.5, 3088. , 3088. ],
[ 3100.5, 3100.5, 3101. , ..., 3101.5, 3101. , 3100.5],
...,
[-3745.5, -3729. , -3722.5, ..., -3734. , -3742. , -3745.5],
[-2940. , -2945. , -2951. , ..., -2895.5, -2921.5, -2940. ],
[-3861. , -3861. , -3861. , ..., -3861. , -3861. , -3861. ]])
Coordinates:
* lon (lon) float64 3kB -180.0 -179.0 -178.0 -177.0 ... 178.0 179.0 180.0
* lat (lat) float64 1kB -90.0 -89.0 -88.0 -87.0 ... 87.0 88.0 89.0 90.0
Attributes:
actual_range: [-7174. 5350.]
long_name: elevation (m)
In [8]: grid2
Out[8]:
<xarray.DataArray 'z' (lat: 181, lon: 361)> Size: 523kB
array([[-3861. , -3861. , -3861. , ..., -3861. , -3861. , -3861. ],
[-2940. , -2945. , -2951. , ..., -2895.5, -2921.5, -2940. ],
[-3745.5, -3729. , -3722.5, ..., -3734. , -3742. , -3745.5],
...,
[ 3100.5, 3100.5, 3101. , ..., 3101.5, 3101. , 3100.5],
[ 3088. , 3087.5, 3087. , ..., 3088.5, 3088. , 3088. ],
[ 2865. , 2865. , 2865. , ..., 2865. , 2865. , 2865. ]])
Coordinates:
* lat (lat) float64 1kB 90.0 89.0 88.0 87.0 ... -87.0 -88.0 -89.0 -90.0
* lon (lon) float64 3kB -180.0 -179.0 -178.0 -177.0 ... 178.0 179.0 180.0
Attributes:
Conventions: CF-1.7
title: SRTM15 Earth Relief v2.5.5 at 01 arc degree
history:
description: Reduced by Gaussian Cartesian filtering (314.5 km fullwidt...
long_name: elevation (m)
actual_range: [-7174. 5350.]
It seems xr.load_dataarray
returns an xarray.DataArray with ascending lon/lat coodinates, but now GMT returns descending latitude. I think I was trying to make GMT_GRID.to_dataaray()
return the exactly same xarray.DataArray object as xr.load_dataarray
. But, maybe there are some misunderstandings here.
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It seems
xr.load_dataarray
returns an xarray.DataArray with ascending lon/lat coodinates, but now GMT returns descending latitude. I think I was trying to makeGMT_GRID.to_dataaray()
return the exactly same xarray.DataArray object asxr.load_dataarray
. But, maybe there are some misunderstandings here.
Hmm yeah, I don't think we need to match the behaviour of xr.load_dataarray
here. I tried with rioxarray.open_rasterio
and it gave descending latitude:
import pygmt
import rioxarray
import xarray as xr
path = pygmt.which("@earth_relief_01d_g", download="a")
grid2 = rioxarray.open_rasterio(path)
print(grid2)
# <xarray.DataArray 'z' (band: 1, y: 181, x: 361)> Size: 131kB
# [65341 values with dtype=int16]
# Coordinates:
# * band (band) int64 8B 1
# * x (x) float64 3kB -180.0 -179.0 -178.0 ... 178.0 179.0 180.0
# * y (y) float64 1kB 90.0 89.0 88.0 87.0 ... -87.0 -88.0 -89.0 -90.0
# spatial_ref int64 8B 0
# Attributes: (12/20)
# lat#actual_range: [-90. 90.]
# lat#axis: Y
# lat#long_name: latitude
# lat#standard_name: latitude
# lat#units: degrees_north
# lon#actual_range: [-180. 180.]
# ... ...
# title: SRTM15 Earth Relief v2.5.5 at 01 arc degree
# actual_range: [-7174. 5350.]
# long_name: elevation (m)
# scale_factor: 0.5
# _FillValue: -32768
# add_offset: 0.0
so we could probably remove the sorting in to_dataarray()
, assuming this doesn't break any of the unit tests.
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I don't think we need to match the behaviour of
xr.load_dataarray
here.
Matching the behavior of xr.load_dataarray
makes it easier to test the output of the virtualfiles using xr.DataArray.indentical
.
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I don't think we need to match the behaviour of
xr.load_dataarray
here.Matching the behavior of
xr.load_dataarray
makes it easier to test the output of the virtualfiles usingxr.DataArray.identical
.
The returned attributes are not the same, so xr.testing.assert_identical
will fail anyway.
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Actually, we're using xr.testing.assert_allclose
in the tests. If we don't sort the coordinates ascendingly, then we have to update all these tests.
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Hmm yeah, I just tried running make test
locally after commenting out the sorting code, and got 19 test failures. Most of these are from the expected_grid
fixture returning a DataArray with y (latitude) sorted in ascending order:
================================================================================== short test summary info ===================================================================================
FAILED ../pygmt/datatypes/grid.py::pygmt.datatypes.grid._GMT_GRID.to_dataarray
FAILED ../pygmt/tests/test_dimfilter.py::test_dimfilter_no_outgrid - AssertionError: Left and right DataArray objects are not close
FAILED ../pygmt/tests/test_grdclip.py::test_grdclip_no_outgrid - AssertionError: Left and right DataArray objects are not close
FAILED ../pygmt/tests/test_grdfill.py::test_grdfill_dataarray_out - AssertionError: Left and right DataArray objects are not close
FAILED ../pygmt/tests/test_grdfill.py::test_grdfill_asymmetric_pad - AssertionError: Left and right DataArray objects are not close
FAILED ../pygmt/tests/test_grdfilter.py::test_grdfilter_dataarray_in_dataarray_out - AssertionError: Left and right DataArray objects are not close
FAILED ../pygmt/tests/test_grdgradient.py::test_grdgradient_no_outgrid - AssertionError: Left and right DataArray objects are not close
FAILED ../pygmt/tests/test_grdhisteq.py::test_equalize_grid_no_outgrid - AssertionError: Left and right DataArray objects are not close
FAILED ../pygmt/tests/test_grdlandmask.py::test_grdlandmask_no_outgrid - AssertionError: Left and right DataArray objects are not close
FAILED ../pygmt/tests/test_grdproject.py::test_grdproject_no_outgrid[M10c] - AssertionError: Left and right DataArray objects are not close
FAILED ../pygmt/tests/test_grdproject.py::test_grdproject_no_outgrid[EPSG:3395 +width=10] - AssertionError: Left and right DataArray objects are not close
FAILED ../pygmt/tests/test_grdproject.py::test_grdproject_no_outgrid[+proj=merc +ellps=WGS84 +units=m +width=10] - AssertionError: Left and right DataArray objects are not close
FAILED ../pygmt/tests/test_grdsample.py::test_grdsample_dataarray_out - AssertionError: Left and right DataArray objects are not close
FAILED ../pygmt/tests/test_surface.py::test_surface_input_file - AssertionError: Left and right DataArray objects are not close
FAILED ../pygmt/tests/test_surface.py::test_surface_input_data_array - AssertionError: Left and right DataArray objects are not close
FAILED ../pygmt/tests/test_surface.py::test_surface_input_xyz - AssertionError: Left and right DataArray objects are not close
FAILED ../pygmt/tests/test_triangulate.py::test_regular_grid_no_outgrid - AssertionError: Left and right DataArray objects are not close
FAILED ../pygmt/tests/test_xyz2grd.py::test_xyz2grd_input_array[array] - AssertionError: Left and right DataArray objects are not close
FAILED ../pygmt/tests/test_xyz2grd.py::test_xyz2grd_input_array[Dataset] - AssertionError: Left and right DataArray objects are not close
======================================================== 19 failed, 657 passed, 4 skipped, 5 xfailed, 2 xpassed, 5 warnings in 58.94s ========================================================
Let's just keep the ascending sort for now then.
@@ -35,8 +33,9 @@ def test_load_remote_dataset_benchmark_with_region(): | |||
assert data.gmt.registration == 0 | |||
assert data.shape == (11, 21) | |||
# The cpt attribute was added since GMT 6.4.0 | |||
if Version(__gmt_version__) >= Version("6.4.0"): | |||
assert data.attrs["cpt"] == "@earth_age.cpt" | |||
# Can't access the cpt attribute using virtual files |
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Ok, so auto colormap won't work after this PR is merged? We'll need to remember to document this in the PyGMT v0.12.0 changelog.
Co-authored-by: Wei Ji <[email protected]>
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Thanks again @seisman for the wonderful work here, from digging into the GMT C code and handling all the grid header parsing! There are still a few limitations such in regard to the CPT attribute and grdtype detection, as you've mentioned in the top post, but we can address that in the future. The speedup improvements will be worth it 😄
@@ -35,8 +33,9 @@ def test_load_remote_dataset_benchmark_with_region(): | |||
assert data.gmt.registration == 0 | |||
assert data.shape == (11, 21) | |||
# The cpt attribute was added since GMT 6.4.0 | |||
if Version(__gmt_version__) >= Version("6.4.0"): | |||
assert data.attrs["cpt"] == "@earth_age.cpt" | |||
# Can't access the cpt attribute using virtual files |
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Ok, let's keep track about this .cpt
attribute idea at #499 (comment).
Description of proposed changes
This PR wraps GMT's standard data type
GMT_GRID
for grids, so that we can store the output grid in GMT virtual files and don't have to write the output grid into a temporary file and load it as xarray.DataArray.Expected enhancements/features
Here is a list of enhancements/features related to the
GMT_GRID
data type:GMT_GRID_HEADER
for grid metadata [Wrap GMT's data structure GMT_GRID_HEADER for grid/image/cube headers #3127]GMT_GRID
for gridsSession.virtualfile_to_raster
method for handling output to an actual file or a virtual file [Similar to theSession.virtualfile_to_dataset
in PR clib: Add virtualfile_to_dataset method for converting virtualfile to a dataset #3083]GMT_GRID
directly to GMT API. Currently, for an xarray.DataArray grid, we first convert it to a matrix, then pass the matrix with some metadata (like inc, registration and gtype) to GMT. This way has proven to cause troubles (e.g., Cylindrical projections 'Q' plot incorrectly in pygmt when using xarrays #390), mainly due to grid paddings. It would be better if we could internally convert xarray.DataArray to GMT_GRID and then pass GMT_GRID to GMT API. It may help us fix many long-term issues. [Will do in future PRs]The
GMT_GRID
/GMT_GRID_HEADER
data structureThe
GMT_GRID
data structure is defined at gmt/src/gmt_resources.h:it contains the x/y array, the data array and the grid header. The grid header
GMT_GRID_HEADER
is defined at gmt/src/gmt_resources.h. It contains many important metadata information about the grid. Here are some important header variables:n_columns
: Number of columnsn_rows
: Number of rowsregistration
: 0 for gridline registration and 1 for pixel registration.wesn
: min/max of x/y coordinates, i.e., [xmin, xmax, ymin, ymax]z_min
/z_max
: min/max of z valuesinc
: x and y increment [should be equal to x[1] - x[0] and y[1] - y[0]]z_scale_factor
/z_add_offset
: Used for data compressing by storing floating-point data as smaller integers in a netCDF file. The relation between the actual data z' and the data stored in netCDF file (z) is z' = z * scale_factor + offset (i.e., unpacking). Need to note that when reading a netCDF file, GMT already does the conversion, soz_min
/z_max
and thedata
array are already unpacked so we usually don't need to care about these two variables.x_units
/y_units
: x/y units in the form oflong_name [units]
. The[units]
part is optional. Some examples are:x
/y
/longitude [degrees_east]
/latitude [degrees_north]
.z_units
: Also in the form oflong_name [units]
.pad
: Extra columns/rows on west/east/south/north sides. Paddings are mainly used for grid manipulations at grid boundary. Defaults are [2, 2, 2, 2].mx
: actual columns in memory. Equal to n_columns + pad[0] + pad[1]my
: actual rows in memory. Equal to n_rows + pad[2] + pad[3]Conversions between netCDF and
GMT_GRID
Although netCDF is the default grid format for I/O, GMT uses the
GMT_GRID
data structure as its internal representation of grids. Thus, GMT needs to convert netCDF data/metadata toGMT_GRID
for input and do the inverse for output. The conversions between netCDF andGMT_GRID
are done by functionsgmt_nc_read_grd
/gmt_nc_write_grd
ingmt/src/gmt_nc.c
. Below Here are some technical notes:x_units
/y_units
/z_units
has the form oflong_name [units]
, in which[units]
is optional.long_name
andunits
are netCDF attributes. gmtnc_get_unitslong_name
andunits
attributes and then sets thex_units
/y_units
/z_units
string. Iflong_name
is not defined, then use the variable's name instead. Ifunits
is not defined, then[units]
is not appended. gmtnc_get_unitslong_name
andunits
attributes by parsing thex_units
/y_units
/z_units
string, and setting the netCDF attributes if they're defined. More attributes are added if it's a geographic coordinate. Ifunits="degrees_east"
, set attributesstandard_name
tolongitude
andaxis
toX
; Ifunits="degrees_north"
, set attributesstandard_name
tolatitude
andaxis
toY
. gmtnc_put_unitslon
/time
/x
for x axis andlat
/time
/y
for y axis. referencez
for 2-D grid orcube
for 3-D cube, unless the variable name is given. The variable name is stored in the hidden structureHH->varname
, but how isHH->varname
determined?. referenceConventions
(CF-1.7
),title
,history
,description
,GMT_version
,node_offset
(only for pixel grids). referenceactual_range
(fromheader-wesn
) andaxis
(X
orY
) are also set. referencescale_factor
(if not 1.0),add_offset
(if not 0.0),cpt
(if defined by GMT),_FillValue
(for NaN),actual_range
.Benefits of current implementation
Limitations of current implementation
In addition to the metadata stored in the
GMT_GRID_HEADER
object, GMT also has some hidden metadata which is stored in a hidden data structure, for example,grdtype
(Cartesian or Geographic grid?),cpt
(the default CPT). The hidden data structure is private and may change between different GMT versions. So it's not a good practice to wrap and use the hidden data structure. But it also means we can't know thegrdtype
/cpt
attributes when convertingGMT_GRID
toxarray.DataArray
.For
grdtype
, it's reasonable to say that the grid is geographic if x's unit isdegrees_east
and y's unit isdegrees_north
(see the note above and also CF conventions), but forcpt
, we can't know if a grid has a default CPT or not.Another limitation is that,
grdcut
now can't cut an image because we assume that the output is a grid. An initial fix is at #3115. But, as far as I can see, although many GMT modules can accept an image (e.g.,grdcut
,grdimage
,grdview
), onlygrdcut
andgrdmix
can output an image.References
gmtnc_put_units
ingmt_nc.c
gmtnc_get_units
ingmt_nc.c
gmtnc_grd_info
ingmt_nc.c
gmt_grd_init
ingmt_grdio.c