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Finding percentage of land cover classes referring to whole except one certain class in a selected polygon

  • May 22, 2023
  • 4 replies
  • 64 views
L

My question is quite simple but I am a new user in FME. Well, I am going through this process in FME workbench to find percentage of land cover classes excluding water bodies.

​

General process:

1- Using selected land cover Shapefile and only consider Grassland (class 30) and cropland (class 40) classes

​

2- Using selected tiles to extract the percent of targeted vegetation (grassland+cropland) referred to the whole classes except water(class 80)

​

3- Select tiles having at least 1% or 0.5% of the targeted vegetation. For info, 1% corresponds to 10 000 ha

​

Below, you can find my fme workflow that it does not work for percentage calculation.

​

I thank you in advance for your guide and feedback.

Best answer by nielsgerrits

I took a look at the worksapce, a couple of things

 

Firstly Area calculations work best when working in a projected coordinate system rather one in LatLong. You should reproject to a different coordinate system before making and Area calculations.

 

Second is that if you want to compare per tile you will also need to add the 'Name' attribute to the group-by in the Dissolvers and the Aggregators otherwise your calculation will not be per tile as teh dissolver will dissolve it all back together again.

 

Addressing these issues should help

The tiles are overlapping, but if you use the Clipper the area's will be assigned to the first tile, not all of them.

2023-05-22_16h14_45As the sentinel data is not overlapping and dissolving is a heavy task, I would leave the Dissolvers out as they are not needed.

I used EPSG:5880 SIRGAS 2000 / Brazil Polyconic but I just picked one from the list, not sure if correct.

Attached a sample how I solved it.

 

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4 replies

virtualcitymatt
Celebrity
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I took a look at the worksapce, a couple of things

 

Firstly Area calculations work best when working in a projected coordinate system rather one in LatLong. You should reproject to a different coordinate system before making and Area calculations.

 

Second is that if you want to compare per tile you will also need to add the 'Name' attribute to the group-by in the Dissolvers and the Aggregators otherwise your calculation will not be per tile as teh dissolver will dissolve it all back together again.

 

Addressing these issues should help

nielsgerrits
VIP
Forum|alt.badge.img+62
  • nielsgerritsVIP
  • Best Answer
  • May 22, 2023

I took a look at the worksapce, a couple of things

 

Firstly Area calculations work best when working in a projected coordinate system rather one in LatLong. You should reproject to a different coordinate system before making and Area calculations.

 

Second is that if you want to compare per tile you will also need to add the 'Name' attribute to the group-by in the Dissolvers and the Aggregators otherwise your calculation will not be per tile as teh dissolver will dissolve it all back together again.

 

Addressing these issues should help

The tiles are overlapping, but if you use the Clipper the area's will be assigned to the first tile, not all of them.

2023-05-22_16h14_45As the sentinel data is not overlapping and dissolving is a heavy task, I would leave the Dissolvers out as they are not needed.

I used EPSG:5880 SIRGAS 2000 / Brazil Polyconic but I just picked one from the list, not sure if correct.

Attached a sample how I solved it.

 

Buckle your seatbelt Dorothy, cause Kansas is going bye-bye...
L
  • lutfi
  • Author
  • May 22, 2023

I took a look at the worksapce, a couple of things

 

Firstly Area calculations work best when working in a projected coordinate system rather one in LatLong. You should reproject to a different coordinate system before making and Area calculations.

 

Second is that if you want to compare per tile you will also need to add the 'Name' attribute to the group-by in the Dissolvers and the Aggregators otherwise your calculation will not be per tile as teh dissolver will dissolve it all back together again.

 

Addressing these issues should help

Thank you so much for your reply.

I made corrections based on your feedback and it is much more fonctional now but still I am having issues with percentage calculations.

L
  • lutfi
  • Author
  • May 23, 2023

The tiles are overlapping, but if you use the Clipper the area's will be assigned to the first tile, not all of them.

2023-05-22_16h14_45As the sentinel data is not overlapping and dissolving is a heavy task, I would leave the Dissolvers out as they are not needed.

I used EPSG:5880 SIRGAS 2000 / Brazil Polyconic but I just picked one from the list, not sure if correct.

Attached a sample how I solved it.

 

Thanks a lot @nielsgerrits​  I applied your corrections on fme workflow and now it seems to be OK. Best of luck🙏

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