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I need to calculate the area of the Building (which the coordinates represents). I used transform() to calculate the area, but the calculated area is not accurate. Please help me calculating the area using the lat/lon coordinates.

          Class Parcel(models.Model):
              geom = models.MultiPolygonField(srid=3492)
              street_nbr = models.CharField(max_length=80)

          Class Primary(models.Model):
              geom  = models.MultiPolygonField(srid=4326)


      >>>parcel = Parcel.objects.filter(street_nbr__contains="2730", street_nam__contains="11TH AVE",city__contains="SACRA").values()
      >>>parcel[0]['geom'].geojson


     >>>build = Primary.objects.filter(goem__contained= parcel[0]['geom'].geojson).values()

     >>>build[0]['geom'].geojson
     '{"coordinates": [[[[-121.476756, 38.542154], [-121.47686, 38.542152], [-121.47686, 38.542136], [-121.476904, 38.542135], [-121.476904, 38.542132], [-121.476962, 38.542131], [-121.476966, 38.542295], [-121.476893, 38.542296], [-121.476892, 38.542278], [-121.476845, 38.542279], [-121.476845, 38.542281], [-121.476759, 38.542282], [-121.476756, 38.542154]]]], "type": "MultiPolygon"}'


      >>>x = build[0]['geom']
      >>>y = x.transform(3492,Clone=True)
      >>>y.area
      1636.8046

Here i'm getting the area as 1636.8046, I was supposed to get 2,327 sqft . I'm not able to find what I am doing wrong.

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1 Answer 1

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If your coordinates are in lat/long, then the SRID should be 4326. So just change the transformation parameter in x.transform.

Try changing y = x.transform(3492,Clone=True) to y = x.transform(4326,Clone=True)

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  • >>> x = build[0]['geom'] >>> y = x.transform(4326,clone=True) >>> y.area 2.9458000000913017e-08 thanks for suggesting me , I tried as you mentioned the above but I'm not aware of Units of the result . Could you please explain me what the result is ?
    – Ballipalli Narendra
    Jul 26, 2018 at 6:45
  • @BallipalliNarendra 2.9458000000913017e-08 is scientific notation for describing very large numbers. In this case it translates to 0.00000002945800000091302, which doesn't seem correct for an area
    – Sam Comber
    Jul 26, 2018 at 8:13
  • 1
    Yes dude area is wrong. I am not getting what i am doing wrong
    – Ballipalli Narendra
    Jul 26, 2018 at 8:15
  • the units for that number is square degrees. Not sure how to fix, though
    – Teddy Ward
    Jul 16, 2019 at 0:08

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