### I want to load orthorectified bands, what do I need to do ?¶

• For Sentinel-3 data, EOReader creates GCPs and uses rasterio.reproject SNAP to geocode the wanted images. The result is slightly different than 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 (with RPC_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 30m 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

## 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 the gpt 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

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.