Enable setting gcps in Reader option

[vincentsarago]

Let's say you have an Non-geo image (as COG already) and some external GCP (e.g from a Georeferencing UI), it would be nice to pass those GCPS to rio_tiler.io.Reader directly to allow virtual georeferencing

rio-tiler/rio_tiler/io/rasterio.py

Lines 98 to 110 in 93cf68e

	def __attrs_post_init__(self):
	"""Define _kwargs, open dataset and get info."""
	if not self.dataset:
	dataset = self._ctx_stack.enter_context(rasterio.open(self.input))
	if dataset.gcps[0]:
	self.dataset = self._ctx_stack.enter_context(
	WarpedVRT(
	dataset,
	src_crs=dataset.gcps[1],
	src_transform=transform.from_gcps(dataset.gcps[0]),
	)
	)
	else:

[vincentsarago]

After couple hours digging, it seems there is no easy solution.
Notes:

• WarpedVRT will no work if the dataset do not have internal GCPS
• I was hopping we could pass a list of gcps to WarpedVRT but it's not possible (the underneath GDAL function won't get it either)

The only solution I found was to create a VRT

import xml.etree.ElementTree as ET
from rasterio.vrt import _boundless_vrt_doc
from rasterio.warp import WarpedVRT

with rasterio.open("image.jpeg") as dataset:
    # Use rasterio boundless_vrt_doc to create a VRT xml document
    vrt_xml = _boundless_vrt_doc(dataset)

    # Update the VRT to add the GCPS
    vrtdataset = ET.fromstring(vrt_xml)
    gcp_list = ET.SubElement(vrtdataset, 'GCPList')
    gcp_list.attrib['Projection'] = str(gcps_crs)
    for gcp in self.gcps:
        g = ET.SubElement(gcp_list, 'GCP')
        g.attrib["Id"] = gcp.id
        g.attrib['Pixel'] = str(gcp.col)
        g.attrib['Line'] = str(gcp.row)
        g.attrib['X'] = str(gcp.x)
        g.attrib['Y'] = str(gcp.y)
    vrt_xml = ET.tostring(vrtdataset)

# Open the VRT Dataset and pass it to the WarpedVRT
with rasterio.open(vrt_xml.decode()) as dataset:
    with WarpedVRT(
        dataset,
        src_crs=dataset.gcps[1],
        src_transform=transform.from_gcps(dataset.gcps[0]),
    ) as vrt:
        ...

Notes:

• I'm not sure what _boundless_vrt_doc does so we might not to check if there are any specifics
• in GDAL if we wanted to allow passing GCPS I thing we would need to update https://github.com/OSGeo/gdal/blob/e641b1356a3ac2ef9f0676fe75f5dc95162afc36/frmts/vrt/vrtwarped.cpp#L139-L298 to allow GDALAutoCreateWarpedVRTEx to set the projection from external GCPS instead of https://github.com/OSGeo/gdal/blob/e641b1356a3ac2ef9f0676fe75f5dc95162afc36/frmts/vrt/vrtwarped.cpp#L292

Ps: I'm going to convert the issue to discussion because there Is no real actionable right now