[gdal-dev] S57 dataset boundary issue

[s duclos]

Nikhil,

I loaded your ENC.

I see a number of depth area (DEPARE) and anchor zone area (ACHARE).

But no inner ring!

Is there an inner rings somewhere I should see?



rgds,

Sylvain.



----- Original Message -----
> From: Nikhil Sai Parupalli <nikhil.parupalli at iictechnologies.com>
> To: s duclos <sylvain_duclos at yahoo.com>; Frank Warmerdam <warmerdam at pobox.com>
> Cc: "gdal-dev at lists.osgeo.org" <gdal-dev at lists.osgeo.org>
> Sent: Wednesday, October 10, 2012 8:00:41 AM
> Subject: RE: [gdal-dev] S57 dataset boundary issue
> 
> Duclos,
> 
> Please see this sample data attached.
> So as per the code given by you we have tried and got result i.e able to find 
> out area 
> 
> some times it shows area<0 and some times area>0 hence we get  CW and CCW.
> But how do we classify in layer which is outer boundary and which is inner 
> boundary
> 
> 
> 
> 
> Geometry testgeo = geomLAKARE.GetBoundary();
>                                     double area = 0;
>                                     for (int l = 0; l < 
> testgeo.GetPointCount() - 1; l++)
>                                     {
>                                         double x1 = testgeo.GetX(l);
>                                         double y1 = testgeo.GetY(l);
>                                         double x2 = testgeo.GetX(l + 1);
>                                         double y2 = testgeo.GetY(l + 1);
>                                         area += (x1 * y2) - (x2 * y1);
>                                     }
> 
> Thanks and Regards
> Nikhil Sai Parupalli
> 
> 
> 
> Note: Do not print this email until and unless it is really required. Save paper 
> , stay Green
> 
> ________________________________________
> From: s duclos [sylvain_duclos at yahoo.com]
> Sent: Tuesday, October 09, 2012 11:58 PM
> To: Frank Warmerdam; Nikhil Sai Parupalli
> Cc: gdal-dev at lists.osgeo.org
> Subject: Re: [gdal-dev] S57 dataset boundary issue
> 
> Frank & Nikhil,
> 
> 
> Frank asked:
> 
>> are, I'm not sure what I or others can do about
>> the performance cost of checking.
> 
> 
> If I understand the problem, then it cost nothing!
> 
> You have to check the winding while loading a OGRGeometryH
> like so:
>                 double area = 0;
>                 for (unsigned int i=0; i<vert_count-1; i++) {
>                     double x1 = OGR_G_GetX(hRing, i);
>                     double y1 = OGR_G_GetY(hRing, i);
>                     double x2 = OGR_G_GetX(hRing, i+1);
>                     double y2 = OGR_G_GetY(hRing, i+1);
>                     area += (x1*y2) - (x2*y1);
>                 }
> 
> 
> If the area < 0 then it is CW (clockwise) and > 0 is CCW (Counter CW).
> 
> Note that in S57 the exterior ring must be CW and
> interior ring are CCW.
> 
> But in S57 there is no order between rings. So interior ring
> might come first. I think WKT fix this. In my code I assume
> that OGR place the exterior ring first.
> 
> 
> We have been trough this before. At the time the question
> 
> was if S57 allow for many exterior ring for the same poly.
> 
> I guess it all depend on HO and how they encode the data.
> 
> I'm using mostly Canadian ENC and found no problem.
> 
> But other HO might encode ENC differently ..
> 
> 
> 
> 
> rdgs,
> 
> 
> Sylvain Duclos.
> 
> 
> 
> 
> 
> 
> 
>> ________________________________
>>  From: Frank Warmerdam <warmerdam at pobox.com>
>> To: Nikhil Sai Parupalli <nikhil.parupalli at iictechnologies.com>
>> Cc: "gdal-dev at lists.osgeo.org" <gdal-dev at lists.osgeo.org>
>> Sent: Tuesday, October 9, 2012 12:25:29 PM
>> Subject: Re: [gdal-dev] S57 dataset boundary issue
>> 
>> 
>> 
>> 
>> 
>> On Mon, Oct 8, 2012 at 10:28 PM, Nikhil Sai Parupalli 
> <nikhil.parupalli at iictechnologies.com> wrote:
>> 
>> HI All,
>>> ,
>>>  
>>> Thanks for the reply in below data
>>> 
>>>   NAME_RCNM (IntegerList) = (7:130,130,130,130,130,130,130)
>>>    NAME_RCID (IntegerList) = (7:691,391,690,52,1336,1503,1512)
>>>    ORNT (IntegerList) = (7:2,2,2,2,1,1,1)
>>>    USAG (IntegerList) = (7:1,1,1,1,1,1,1)
>>>    MASK (IntegerList) = (7:255,255,255,255,255,255,255)
>>> 
>>>  RCID 691 ORNT has  2 and USAG is 1 based on this data we could identify 
> that RCID 691 is of exterior boundary with reverse direction.
>>> 
>>> So if I have 1000 RCID in  NAME_RCID which is vise versa for the above 
> condition I need to display that RCIDS list as errors.
>>> So it makes 1000 conditional checks hence reducing performance.
>>> 
>>> Please let us know further.
>> 
>> 
>> Nikhil,
>> 
>> 
>> I'm afraid I don't follow your point.  Are you trying to
>> do some sort of ring orientation validation and identify
>> ones that don't match your expectations?  And you
>> are concerned about the performance cost?
>> 
>> 
>> I don't know why you are doing this, and if you
>> are, I'm not sure what I or others can do about
>> the performance cost of checking.
>> 
>> 
>> Best regards,--
>> ---------------------------------------+--------------------------------------
>> I set the clouds in motion - turn up   | Frank Warmerdam, 
> warmerdam at pobox.com
>> light and sound - activate the windows | http://pobox.com/~warmerdam
>> and watch the world go round - Rush    | Geospatial Software Developer
>> 
>> 
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>> 
>> 
>