Frequently Asked Questions (FAQ)
Frequently Asked Questions (FAQ)#
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.reprojectto geocode the wanted images. However, the result is slightly different from the one obtained by SNAP.
For SAR images, EOReader uses SNAP to orthorectify the wanted images.
For VHR data, if not already orthorectified, EOReader will use
RPC_DEMkeyword) 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 ?)
gdalwarpcannot access DEM through S3-compatible storage or https links. Be sure to link a DEM stored on disk.
This step is very time-consuming as the whole stack is reprojected for once. It may even never finish on your computer with very big images (sometimes VHR data can weight more than 15Go). It is best to give an already orthorectified stack on the side, you can see an example in the VHR Notebook
For other constellations, 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 !
Dask is a functionality not really tested on EOReader, use it at your own risk
⚠ Be sure to use SNAP 8.0 or more, and please verify that your software is up-to-date.
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
However, it seems that SNAP can only use TIF dems…
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)
SNAP known bugs#
Absolute radiometric calibration has already been applied to the product#
If SNAP 8.0 is used without any updates, the calibration step seems not be able to be skipped if the calibration step has already been applied. (see this issue) This is resolved when the software is updated.
Using SNAP 9.0 also resolves this.
secure-processing not recognized#
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
Please look at this issue for more information.
COSMO-SkyMed orthorectified files are empty#
For an unknown reason, the SNAP calibration step doesn’t work and set nodata everywhere.
A workaround is to set the file
cplx_no_calib_preprocess_default.xml stored in
eoreader/data in the
EOREADER_PP_GRAPH environment variable.
Even if the product won’t be calibrated, you will be able to work with some orthorectified data.
import os os.env["EOREADER_PP_GRAPH"] = "/home/eoreader/data/cplx_no_calib_preprocess_default.xml" prod.load(VV)