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Reading Sentinel-3 raster data In Fme Desktop - NetCDF

  • February 25, 2019
  • 6 replies
  • 45 views
adriano
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Has anyone had success reading FME Sentinel-3 data in FME Desktop?

 

I am attempting to read in the level 2 OLCI Terrestrial Chlorophyll Index but their data does not come with any coordinate system within the netcdf but rather in a completely separate unrelated file which is not compatible GIS Software.

 

My question is how to properly read in Sentinel-3 data in fme desktop? Their documentation only provides a method for converting the data into a geotiff but unfortunately their software does not indicate the coordinate system of the data.

 

https://step.esa.int/docs/tutorials/S3TBX_Data_conversion_and_export_in_SNAP.pdf

 

 

 

After contacting their team about what coordinate system this data uses, their response was:

 

 

"I am afraid you won’t find any information related to the coordinate system in the documentation.

The data are provided in a projection linked to the satellite.

-Along track the resolution is OLCI acquisition rate (~0.044 s)

-Across track the sampling is 270 m (see value in the product manifest); frames are perpendicular to the satellite direction."

 

 

I didn't find their explanation very helpful.

 

 

Any suggestions?

6 replies

jdh
Contributor
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  • jdhContributor
  • Contributor
  • February 25, 2019

You should have a netcdf file called geo_coordinates.nc.

 

 

This contains 3 rasters, with the Longitude, Latitude and Altitude for each pixel.

 

 

 

FME can read it, and you can do some manipulations to turn your data into a point cloud, or individual points.

 

 

Note that the lat/long is stored in an integer format, I believe by a factor of 1e6.

 

 

adriano
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  • adriano
  • Author
  • February 25, 2019
jdh wrote:

You should have a netcdf file called geo_coordinates.nc.

 

 

This contains 3 rasters, with the Longitude, Latitude and Altitude for each pixel.

 

 

 

FME can read it, and you can do some manipulations to turn your data into a point cloud, or individual points.

 

 

Note that the lat/long is stored in an integer format, I believe by a factor of 1e6.

 

 

yup i see the geo_coordinates.nc file which has those attributes! Do we really need the altitude band or just the lat and long?

 

What manipulations did you do exactly to convert it to a point cloud? Did you use the "RasterBandCombiner" to combine all 3 raster layers into 1 single raster with 3 bands (lat,long,OLCI Terrestrial Chlorophyll Index)?

jdh
Contributor
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  • jdhContributor
  • Contributor
  • February 25, 2019
adriano wrote:

yup i see the geo_coordinates.nc file which has those attributes! Do we really need the altitude band or just the lat and long?

 

What manipulations did you do exactly to convert it to a point cloud? Did you use the "RasterBandCombiner" to combine all 3 raster layers into 1 single raster with 3 bands (lat,long,OLCI Terrestrial Chlorophyll Index)?

You would only need the altitude band if you were working in 3D.

 

Yes, all necessary bands were combined into a single raster.

 

 

Attached is a proof of concept workflow. I ended up just coercing to individual points. You could turn them into a point cloud, or rasterize them.

 

 

Looking at my sample, they do appear to be spatially aligned, so you may decide that it's not worth the expense (time) of coercing the pixels, but rather getting the coordinates of the 4 corners and determining the affine transformation.

 

 

adriano
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  • adriano
  • Author
  • February 25, 2019
jdh wrote:

You would only need the altitude band if you were working in 3D.

 

Yes, all necessary bands were combined into a single raster.

 

 

Attached is a proof of concept workflow. I ended up just coercing to individual points. You could turn them into a point cloud, or rasterize them.

 

 

Looking at my sample, they do appear to be spatially aligned, so you may decide that it's not worth the expense (time) of coercing the pixels, but rather getting the coordinates of the 4 corners and determining the affine transformation.

 

 

wow this is great. Thanks for taking the time to put this together. I want to work with the data as a raster instead of a point cloud so I am going to do some further tweaking!

jdh
Contributor
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  • jdhContributor
  • Contributor
  • February 25, 2019
adriano wrote:

wow this is great. Thanks for taking the time to put this together. I want to work with the data as a raster instead of a point cloud so I am going to do some further tweaking!

You happened to say the magic word "Sentinel" while I was on my lunch break.

 

Good luck with this. What I did was a very brute force approach, and may not be the best for production work.
adriano
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  • adriano
  • Author
  • February 25, 2019
jdh wrote:

You happened to say the magic word "Sentinel" while I was on my lunch break.

 

Good luck with this. What I did was a very brute force approach, and may not be the best for production work.

Is it possible in fme to keep it as a raster with it's correct geoloction for each pixel without having to convert it to points in fme? You used the vertex creator in order to assign it to the correct lat long but I'm not sure what raster transformer would have this functionality?

 

 

When attempting to convert the points back to a raster using the image rasterizer, it doesn't come out quote right.

 

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