請問在Stata中如何根據座標計算任意多邊形的面積和中心

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各位前輩，
      最近遇到一個比較棘手的問題，我現有一個省份的鄉鎮市區的boundary的座標（經緯度），希望通過stata來計算這些鄉鎮市區的面積和中心，請問各位前輩具體的語法應該怎麼寫。我之前在網路查過一個Pro.Nick寫的Program ,試著運行但是數據沒有什麽變化，即是我的data當中并沒有產生一個新的叫area的變項。
      以下是語法
      *! NJC 1.0.0 15 August 2003
program polyarea, rclass
version 12
syntax varlist(min=2 max=2 numeric) [in]

tokenize `varlist'
args x y

marksample touse, novarlist
qui count if `touse' & (missing(`x') | missing(`y'))
if r(N) {
di as err "missing values in data"
exit 198
}

tempvar order area

gen long `order' = _n
su `order' if `touse', meanonly

qui gen `area' = `touse' * ///
(`x'[_n + 1] - `x') * (`y'[_n + 1] + `y') / 2
qui replace `area' =       ///
(`x'[`r(min)'] - `x') * (`y'[`r(min)'] + `y') / 2 in `r(max)'
su `area', meanonly

di as res %9.0g abs(r(sum))
return scalar area = abs(r(sum))
end


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关键词：Stata tata marksample meanonly Boundary 如何 中心

it looks like the program return the area in scalar, not a variable in data.  If you do

sca list area

does it show anything?

jjjj6666 发表于 2014-2-13 05:19
it looks like the program return the area in scalar, not a variable in data.  If you do

sca list  ...

thanks a lot for your concern ,I have tried your suggestion"sca list area"but failed    Stata showed the result below
sca list area
scalar area not found
r(111);

sorry, it return the sca in return list, using "di r(area)" instead.

also, when calling this program, did you get any error?

jjjj6666 发表于 2014-2-14 01:07
sorry, it return the sca in return list, using "di r(area)" instead.

also, when calling this prog ...

hello,so grateful for your help.I have tried "di r(area)"but nothing showed in the scree.That is the trouble it seems that the program runs successfully without any erro ,but I can't get the value of area.

can you post the data with the x y variables only if it's not big? It seems the program will output something, at least.

jjjj6666 发表于 2014-2-14 04:27
can you post the data with the x y variables only if it's not big? It seems the program will output  ...

yes I post my data named "data sample.xlsx" in the appendix at the end of my question .do you notice it .

测试的结果，请参考

thanks.  So, it does show the result in r(area), and I think sysuxiaogui can get the result from r(area) easily.

jjjj6666 发表于 2014-2-14 21:51
thanks.  So, it does show the result in r(area), and I think sysuxiaogui can get the result from r(a ...

Dear J,I have tried di r(area) but get nothing .you use Stata version12.0 or others?