Frequently Asked Questions (FAQ)
Contents
Frequently Asked Questions (FAQ)¶
EOReader¶
I want to load orthorectified bands, what do I need to do ?¶
EOReader always loads orthorectified bands, you cannot get raw bands !
For Sentinel-3 data, EOReader creates GCPs and uses
rasterio.reproject
SNAP to geocode the wanted images. The result is slightly different from the one obtained by SNAP !For SAR images, EOReader uses SNAP to orthorectify the wanted images.
For DIMAP data, if not already orthorectified, EOReader will use
rasterio.reproject
(withRPC_DEM
keyword) to orthorectify the DIMAP stack.
However, this comes with several limitations:Pay attention to give a sufficiently resolute DEM (does orthorectifying Pleiades data with a 30 m SRTM DEM make sense ?)
gdalwarp
cannot access DEM through S3-compatible storage or https links. Be sure to link a DEM stored on disk.
For other sensors, non-orthorectified bands are not supported yet.
I want to load projected bands, what do I need to do ?¶
EOReader always loads projected bands (in UTM). This may be an issue for:
Sentinel-3 data that are very wide and may have inaccurate georeferencing.
DIMAP data provided in WGS84 that need reprojection (and therefore time-consuming processes)
If needed, we could change this to allow WGS84 representation. If so, do not hesitate to open an issue on GitHub !
I want to use Dask with EOReader, what should I do ?¶
First of all, be sure to have dask[distributed]
installed in your environment.
Then set the environment variable EOREADER_USE_DASK
to 1.
The bands will be read and written using rioxarray
’s dask functionalities,
see here for more information.
However, EOReader still relies a lot on rasterio
(to orthorectify DIMAP products for example) or on SNAP,
and these functions cannot be daskified. A lot of optimizations are left to do, do not hesitate to help us on that !
Warning
Dask is a functionality not really tested on EOReader, use it at your own risk
SNAP¶
SNAP DEM vs other DEM¶
SNAP has a capability to use its own DEMs. This does not interfere with the DEM provided to load a DEM band for example.
However, you can force SNAP to use your own DEM (stored in EOREADER_DEM_PATH
, providing your DEM is compatible)
by setting the environment variable EOREADER_SNAP_DEM_NAME
to External DEM
.
What SNAP’s GPT optimizations are you using ?¶
We are using some optimizations in order to optimize SNAP’s GPT speed, as specified here
Memory: We are allowing GPT to use 95% of your max virtual memory
CPU: We are allowing GPT to use
max_core
- 2 cores of your computer (i.e. 14 cores out of 16)Tiles: Width and height are set to 2048 pixels (instead of 512x512) and cache to 50% of your max memory (instead of 1024Mo)
I have installed EOReader with Conda and I have troubles with SNAP¶
Please remember that conda modifies your
PATH
, so thegpt
exe can be lost.
Do not hesitate to include it once again. For example:
import os
os.environ["PATH"] += r";C:\Program Files\snap\bin"
Sometimes a weird bug appears with conda and the .xml files stored in
eoreader/data
are not in the conda package.
If it happens, please post an issue and in the meantime download them from Github, then set the graphs by hand:
import os
os.environ["EOREADER_PP_GRAPH"] = r"your/path/to/grd_s1_preprocess_default.xml" # if you are analyzing S1 GRD data
os.environ["EOREADER_DSPK_GRAPH"] = r"your/path/to/sar_despeckle_default.xml"
Known SNAP bugs¶
Sometimes SNAP process returns Feature 'http://javax.xml.XMLConstants/feature/secure-processing' is not recognized.
This is a known SNAP bug.
Just add the line -Djavax.xml.parsers.SAXParserFactory=com.sun.org.apache.xerces.internal.jaxp.SAXParserFactoryImpl
to your gpt.vmoptions
file.
Please look at this issue for more information.