Average NDVI from a polygon

Apps / Services
#1

Hello,

I’m getting started accessing the Process API (S2L1C) and I need to get the minimum, maximum and average ndvi from a polygon.

I’ve already getting the TIFF file with the desired colors, but I don’t know where to start to get those values in the response.

I’m using CURL and PHP.

Any help would be appreciated.

#2

Hi @marcos.fbc,

the easiest way is to use a dedicated API for this - Statiatical API.

The other option is using updateOutputMetadata function of the custom script as demonstrated in Tip 6 in this blog:

1 Like
#3

Thanks for your quick response.
I`ll try both today.

#4

Hi @gmilcinski,

Thanks again for your response.
I’m trying to use Statiacical API, but when I changed the region using GEOMETRY the response was empty.

Actually I needed to add RESX and RESY to my request as well.

http://services.sentinel-hub.com/ogc/fis/4f9e0919-3206-MASKED?LAYER=VEGETATION-INDEX-NDVI&STYLE=INDEX&CRS=EPSG:3857&TIME=2018-11-15%2F2020-05-15&GEOMETRY=POLYGON((-54.08952876561413 -27.98739282040455,-54.08336551369231 -27.98760544600711,-54.08459142114501 -27.98144772947314,-54.08738735387322 -27.97536276995694,-54.08843974280309 -27.97533191400677,-54.08908634398883 -27.97588577227436,-54.09016603092668 -27.97696274098633,-54.09139788028573 -27.97760384874638,-54.08986613010527 -27.98277768003278,-54.08952876561413 -27.98739282040455))&MAXCC=5&RESX=512&RESY=512

Any ideas why is it happening?

#5

There are several problems in your request:

  • CRS is defined as EPSG:3857, yet your geometry is provided in EPSG:4326
  • geometry should be provided in latitude/longitude order
  • RESX and RESY should not appear in Statistical API, used RESOLUTION instead
  • RESOLUTION should be provided in the same units as the CRS, e.g. in degrees in your case; there is an exception in case of Statistical API, that you can use RESOLUTION=10m if you want us to give a best try to convert these “10 meters into degrees at your latitude”

Applying all of this you get a request, that works:

http://services.sentinel-hub.com/ogc/fis/4f9e0919-3206-4690-MASKED?LAYER=VEGETATION-INDEX-NDVI&STYLE=INDEX&CRS=EPSG:4326&TIME=2018-11-15%2F2020-05-15&GEOMETRY=POLYGON((-27.98739282040455 -54.08952876561413, -27.98760544600711 -54.08336551369231, -27.98144772947314 -54.08459142114501, -27.97536276995694 -54.08738735387322, -27.97533191400677 -54.08843974280309, -27.97588577227436 -54.08908634398883, -27.97696274098633 -54.09016603092668, -27.97760384874638 -54.09139788028573, -27.98277768003278 -54.08986613010527, -27.98739282040455 -54.08952876561413))&MAXCC=5&RESOLUTION=10m

Note that I have masked part of your instance ID to prevent other readers of this forum to abuse it.

1 Like
#6

@gmilcinski,

I already tested here and it’s working fine.

Thank you for your help