How to extract the correct longitude/latitude from a OLCI L2 FR data?

s3tbx
#1

Data source: S3A_OL_2_WFR____20170808T015825_20170808T020125_20170808T035817_0179_021_003_2340_MAR_O_NR_002.SEN3

When I am trying to extract the longitude/latitude from OLCI data using Python, I am a bit confused.
(1) I read longitude/latitude from “geo_coordinates.nc” which are stored as INT32. For example, [116331531, 42158803] @ pixel[0,0] which is translated to [116.331531, 42.158803]
(2)It reads as [116.33295, 42.15732] when I put the pointer on pixel[0,0].
(3)When I extracted pixel info using “copy pixel-info to clipboard”, it gave me two sets of longitude/latitude info.
“Image-X: 0 pixel
Image-Y: 0 pixel
Longitude: 116°19’59” E degree
Latitude: 42°09’27" N degree"
and
“altitude: 0 m
latitude: 42.1588030000 degrees_north
longitude: 116.3315310000 degrees_east” this one is equal to (1)

which one should I use?

#2

In the file geo_coordinates.nc the coordinates are stored for each pixel but there is another file where geo-coordinates are stored on a tie-point grid. It’s named tie_geo_coordinates.nc. They are less accurate but working with them is faster.
In your pixel-info export, the Longitude and Latitude values (in degrees minutes seconds) are taken from the tie-points. The latitude and longitude values (in decimal degrees) are taken from the per-pixel bands.
By default, SNAP uses the tie-points. You can switch to the per-pixel geo-coordinates in the options dialogue.

image.png752×368 27.3 KB

Afterwards they should be equal.

#3

I got it.
Thanks. Marpet.

#4

Sir, Hello:
The SZA, SAA, OZA, OAA are not stored for each pixel in any file. In the tie_geometrics.nc they are stored on a tie-point grid. But there is more information about beginning point and interval of this grid. Can you tell detail? Thanks