From 292721ecd94ada4688f073818540d8e56b259398 Mon Sep 17 00:00:00 2001
From: Brendan Collins <brendancol@gmail.com>
Date: Wed, 13 May 2026 21:08:24 -0700
Subject: [PATCH] geotiff: VRT writer emits Int64/UInt64 for 64-bit integer
 sources (#1833)

The dtype lookup in write_vrt had no entry for bps=64, so signed 64-bit
sources fell back to Int32 and unsigned 64-bit sources fell back to Byte.
The VRT reader has UInt64/Int64 support already (issue #1783), so the
loss happened on write -- uint64 values silently truncated to [0, 255].

Add 64-bit entries to both lookups so write_vrt and to_geotiff(..., '*.vrt')
round-trip 64-bit integer rasters losslessly.
---
 xrspatial/geotiff/_vrt.py                     |  8 +-
 .../tests/test_vrt_writer_int64_1833.py       | 75 +++++++++++++++++++
 2 files changed, 81 insertions(+), 2 deletions(-)
 create mode 100644 xrspatial/geotiff/tests/test_vrt_writer_int64_1833.py

diff --git a/xrspatial/geotiff/_vrt.py b/xrspatial/geotiff/_vrt.py
index 49e38708..553d939f 100644
--- a/xrspatial/geotiff/_vrt.py
+++ b/xrspatial/geotiff/_vrt.py
@@ -1363,9 +1363,13 @@ def _pixel_size_mismatch(a: float, b: float) -> bool:
     if sf == 3:
         vrt_dtype_name = 'Float64' if bps == 64 else 'Float32'
     elif sf == 2:
-        vrt_dtype_name = {8: 'Int8', 16: 'Int16', 32: 'Int32'}.get(bps, 'Int32')
+        vrt_dtype_name = {
+            8: 'Int8', 16: 'Int16', 32: 'Int32', 64: 'Int64',
+        }.get(bps, 'Int32')
     else:
-        vrt_dtype_name = {8: 'Byte', 16: 'UInt16', 32: 'UInt32'}.get(bps, 'Byte')
+        vrt_dtype_name = {
+            8: 'Byte', 16: 'UInt16', 32: 'UInt32', 64: 'UInt64',
+        }.get(bps, 'Byte')
 
     srs = crs_wkt or first.get('crs_wkt') or ''
     nd = nodata if nodata is not None else first.get('nodata')
diff --git a/xrspatial/geotiff/tests/test_vrt_writer_int64_1833.py b/xrspatial/geotiff/tests/test_vrt_writer_int64_1833.py
new file mode 100644
index 00000000..7e4b0751
--- /dev/null
+++ b/xrspatial/geotiff/tests/test_vrt_writer_int64_1833.py
@@ -0,0 +1,75 @@
+"""Regression tests for VRT writer 64-bit integer dtype handling.
+
+``write_vrt`` (and ``to_geotiff(da, "*.vrt")`` by extension) previously
+mapped signed 64-bit source rasters to ``Int32`` and unsigned 64-bit
+source rasters to ``Byte`` because the dtype lookup had no entry for
+``bps=64`` and fell back to the small-int default. The VRT reader has
+explicit ``UInt64`` / ``Int64`` support (see issue #1783), so the loss
+happened on write -- silently truncating uint64 values to ``[0, 255]``.
+
+See issue #1833.
+"""
+from __future__ import annotations
+
+import re
+
+import numpy as np
+import xarray as xr
+
+from xrspatial.geotiff import open_geotiff, to_geotiff
+
+
+def _da(arr: np.ndarray) -> xr.DataArray:
+    h, w = arr.shape
+    return xr.DataArray(
+        arr,
+        dims=('y', 'x'),
+        coords={'y': np.arange(h, dtype=np.float64),
+                'x': np.arange(w, dtype=np.float64)},
+        attrs={'res': (1.0, 1.0)},
+    )
+
+
+def _read_vrt_dtype_attr(vrt_path: str) -> str:
+    """Extract the ``dataType`` attribute from the emitted VRT XML."""
+    with open(vrt_path) as f:
+        xml = f.read()
+    m = re.search(r'dataType="([^"]+)"', xml)
+    assert m is not None, f"no dataType attribute in VRT:\n{xml}"
+    return m.group(1)
+
+
+def test_uint64_vrt_writer_declares_uint64(tmp_path):
+    big = np.iinfo(np.uint64).max
+    arr = np.array([[1, 2], [big - 7, big]], dtype=np.uint64)
+    vrt = tmp_path / 'u64_1833.vrt'
+    to_geotiff(_da(arr), str(vrt))
+    assert _read_vrt_dtype_attr(str(vrt)) == 'UInt64'
+
+
+def test_int64_vrt_writer_declares_int64(tmp_path):
+    info = np.iinfo(np.int64)
+    arr = np.array([[info.min, -1], [0, info.max]], dtype=np.int64)
+    vrt = tmp_path / 'i64_1833.vrt'
+    to_geotiff(_da(arr), str(vrt))
+    assert _read_vrt_dtype_attr(str(vrt)) == 'Int64'
+
+
+def test_uint64_vrt_round_trip(tmp_path):
+    big = np.iinfo(np.uint64).max
+    arr = np.array([[1, 2], [big - 7, big]], dtype=np.uint64)
+    vrt = tmp_path / 'u64_rt_1833.vrt'
+    to_geotiff(_da(arr), str(vrt))
+    r = open_geotiff(str(vrt))
+    assert r.dtype == np.uint64
+    np.testing.assert_array_equal(np.asarray(r.values), arr)
+
+
+def test_int64_vrt_round_trip(tmp_path):
+    info = np.iinfo(np.int64)
+    arr = np.array([[info.min, -1], [0, info.max]], dtype=np.int64)
+    vrt = tmp_path / 'i64_rt_1833.vrt'
+    to_geotiff(_da(arr), str(vrt))
+    r = open_geotiff(str(vrt))
+    assert r.dtype == np.int64
+    np.testing.assert_array_equal(np.asarray(r.values), arr)