[Shapelib] Adding a polygon to a shapefile

[Tom Kazimiers]

Joaquin,

sorry - I missed that you actually do have first and last elements the 
same of your vertex arrays :)
But could you please write down where the error appears and what kind of 
error it is?

cheers,
Tom

Tom Kazimiers schrieb:
> Hi Joaquin,
>
> as fas as I understood you can not make this call:
> psObject = SHPCreateObject(nShapeType, ShapeId, nParts, panParts, 
> NULL, vertexcount, X, Y, NULL, NULL );
>
> have you checked if osObject is null afterwards? Please try it.
> Could it be that the first and the last vertex of a polygon need to be 
> the same? In your code they are different.
> For my writing I use: SHPCreateSimpleObject which implys some NULLs of 
> yours - maybe you could try this, too.
>
> bye,
> Tom
>
>
> Joaquin Perez Valera schrieb:
>> Hi
>>
>> I can create shapefiles and they are valid when I work with 
>> ArcCatalog. But the shapefiles are empty.
>>
>> Now I'm trying to add objects to my shapefile. I want to add polygons.
>>
>> First I create a shapefile and a dbf file with an a simple column. 
>> Then it becomes valid for ArcCatalog.
>> Then I create 2 arrays of 7 elements X[7] and Y[7], and give a valor 
>> to each element. Seven elements because
>> I want to draw a polygon of six vertices.
>>
>> After it I use psObject = SHPCreateObject to create my polygon and 
>> after   SHPWriteObject( hSHP, -1, psObject ); to write it
>> in my shapefile.
>>
>> It's obviously that I'm doing something wrong.
>> But I don't know what.
>>
>> Can somebody help me or say me what I'm doing wrong?
>>
>> Thanks.
>>
>>
>> [CODE]
>> #include <iostream>
>> #include <cstdlib>
>> #include "shapefil.h"
>> #include "string.h"
>>
>>
>> using namespace std;
>> int main()
>>
>> {
>>     SHPHandle    hSHP;
>>     DBFHandle    hDBF;
>>     int        nShapeType,   nWidth = 3, vertexcount, *panParts, 
>> ShapeId, nParts;
>>
>>     string  shape_name, Col1;
>>     Col1= "Column";
>>       SHPObject    *psObject;
>>          cout << "Name of the new Shapefile" << endl;
>>     getline(cin,shape_name);
>>
>>     cout << "The shapefile is: " << shape_name << endl;
>>
>>     //Here I define the type of shapefile, the 5 is for a polygon.
>>     nShapeType=5;
>>           hSHP = SHPCreate( shape_name.c_str(), nShapeType );
>>  
>>     hDBF = DBFCreate( shape_name.c_str() );
>>                  cout <<"The shape has "<< DBFGetFieldCount( hDBF ) 
>> <<" columns" << endl;
>>            DBFAddField( hDBF, Col1.c_str(), FTInteger,   nWidth, 0 );
>>     cout <<"Now the shape has " << DBFGetFieldCount( hDBF ) << " 
>> columns";
>>        //At this point the shape is valid for ArcView
>>
>>     //Here I define an array of seven elements and I'll give a 
>> coordinate for each element
>>        double X[7], Y[7];
>>     X[0] = 220764;
>>     Y[0]= 2343777;
>>     X[1] = 220610;
>>     Y[1]= 2343627;
>>     X[2] = 220818;
>>     Y[2]= 2343477;
>>     X[3] = 221109;
>>     Y[3]= 2343777;
>>     X[4] = 230504;
>>     Y[4]= 2343627;
>>     X[5] = 221102;
>>     Y[5]= 2343477;
>>     X[6] = X[0];
>>     Y[6] = Y[0];
>>           //I know the number of vertex is 7, six of my polygon and 
>> an extra
>>     //vertex to close the polygon.
>>        vertexcount = 7;
>>        //I can't understand what is exactly the panParts variable. :(
>>        panParts[0] = 1;
>>     //What is nParts? For me my polygon has 1 part, an entire part. 
>> It is true?
>>     nParts = 1;
>>     //I give a shape id for this unique object.
>>     ShapeId=1;
>>    //From the shp_api I took this line of code to create a 
>> feature/object
>> //SHPCreateObject( nSHPType, iShape, nParts, panPartStart, 
>> panPartType,int nVertices, *padfX, * padfY, *padfZ, *padfM );
>> //I have the nShapeType;
>> //I give the ShapeId
>> //I give the nParts
>> //I don't know what is panParts
>> //panPartType is NULL because it isn't a multipatch file
>> //I know the numer of vertex
>> //I now the number of vertex I have two arrays of coordinates.
>> //padfZ and padfM are NULL, zero.
>>
>>     psObject = SHPCreateObject(nShapeType, ShapeId, nParts, panParts, 
>> NULL, vertexcount, X, Y, NULL, NULL );
>>        SHPWriteObject( hSHP, -1, psObject );
>>        SHPDestroyObject( psObject );
>>        DBFClose( hDBF );
>>       SHPClose( hSHP );
>>               return 0;
>> }
>>
>> [/CODE]
>>
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