Estimate the vegetation area included in the ellipse(about footprint)

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Estimate the vegetation area included in the ellipse(about footprint)

JINHUI
Hello!

1.To estimate the vegetation area included in each ellipse, which spatial analysis fountion could I use?

2. I would like to know how to estimate the vegetation area included in each ellipse, which spatial analysis fountion could I use to  "cut" the vegetation polygons with each ellipse?

3.I try to use the ST_intersection but failed,I can not get the intersection of the geom and the footprint;

--create table cont_veg as select a.Time, a.Wdir,a.z0,a.KM_p01a,a.KM_p01b,a.KM_p01c, ST_area(st_intersection(a.footprint, b.ST_Union)) as veg_cont from footprint_ART_def a,veg_uni  b where st_intersects(a.footprint, b.ST_Union);
and could you tell me the exactly meaning of the 'veg_cont'?

4.For the rotation angle (radians) of the ellipse in the x,y projection (in ST_makeellipse) how can I get it ?

Thanks in avance!!!

Jinhui chen
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Re: Estimate the vegetation area included in the ellipse(about footprint)

Gwendall Petit
Administrator
Hi,

Maybe you don't remember the exercices done in courses ... but we already answered this kind of questions.

You have two kind of geometries :
  1- the vegetation area (polygon)
  2- the footprint area (polygon) --> ellipse

So if you you want to determine, in each ellipse the area of vegetation, you have to cut (with st_intersection) the vegetation which is in an ellipse (better to choose ST_Intersect).
When the vegetation is cutted, you have to sum the area (ST_Area) of each pieces that are in each ellipses.

Hope it helps,

Regards

Gwendall
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Re: Estimate the vegetation area included in the ellipse(about footprint)

JINHUI


the information of the ellipse

sorry,I don't know how to let the picture more clear
and the information about the ellipse is

id Time Wdir Z0 KM_P01a KM_P01b KM_P01c   footprint
                                                                         POLYGON((......))
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Re: Estimate the vegetation area included in the ellipse(about footprint)

JINHUI
In reply to this post by Gwendall Petit
Good morning,my dear professor Gwendall,

I have alrealy cutted the footprint and try to analysis the area of vegetation in the ellipse ,
but I try to get the area of the ellipse,but failed,and for the ellipse,I only get the information like:

--select sum(footprint) from footprint_ART_g260;
for this founction, I should first translate footprint to geom?or not?(How?)

Jinhui