[gdal-dev] Need help if OGR C-API

[Stephen Woodbridge]

On 9/3/2010 1:04 PM, Frank Warmerdam wrote:
> Stephen Woodbridge wrote:
>> Hi all,
>>
>> Trying to convert a shapelib program over to OGR and have to say it is
>> very complicated.
>>
>> I'm using: GDAL 1.7.2, released 2010/04/23
>>
>> At the moment I stuck on:
>>
>> hDSin = OGROpen( "Streets.shp", FALSE, NULL );
>> hLayerIn = OGR_DS_GetLayerByName( hDSin, "Streets" );
>>
>> hFDefnIn = OGR_L_GetLayerDefn( hLayerIn );
>> layerGeomType = OGR_FD_GetGeomType( hFDefnIn );
>>
>> And always returns: layerGeomType == wkbUnknown
>>
>> And OGR_L_GetGeomType( hLayerIn ) does not appear until 1.8.
> ...
>
>> So how do I get the geometry type of the shapefile?
>
> Steve,
>
> Hmm, that's odd. You should be getting wkbLineString or wkbLineString25D.
> Does ogrinfo report the layer type properly? It is essentially using
> the same mechanism. Perhaps GDAL/OGR 1.7.2 did not always return the layer
> geometry type - it is technically inaccurate to return wkbLineString since
> the shapefile could also contain multilinestrings and we can't know unless
> they are all read which we don't want to do on open.
>
> The current trunk code reports linestring, but this is an area of behavior
> on which I have vacillated (correctness vs. handiness).
>

Hi Frank,

One thing that would be very nice is to change the name space for the 
embedded shapelib function so libshp can be linked to a program with 
ogr. I can see that using ogr has lots of benefits, but it is 
complicated relative shapelib if that is all you need.

Back to the current problem, here is what shpdump reports and ogrinfo. 
These both look ok.

-Steve

woodbri at mappy:~/dev/elevation$ shpdump Streets.shp | head
Shapefile Type: Arc   # of Shapes: 102958

File Bounds: (     -71.889,      42.157,0,0)
          to  (     -71.021,      42.734,0,0)

Shape:0 (Arc)  nVertices=3, nParts=1
   Bounds:(     -71.563,      42.267, 0, 0)
       to (     -71.563,      42.267, 0, 0)
      (     -71.563,      42.267, 0, 0) Ring
      (     -71.563,      42.267, 0, 0)


ogrinfo  Streets.shp Streets
INFO: Open of `Streets.shp'
       using driver `ESRI Shapefile' successful.

Layer name: Streets
Geometry: Line String
Feature Count: 102958
Extent: (-71.888528, 42.156701) - (-71.020913, 42.734315)
Layer SRS WKT:
(unknown)
LINK_ID: Integer (10.0)
NAME: String (80.0)
L_REFADDR: Integer (10.0)
L_NREFADDR: Integer (10.0)
L_SQLNUMF: String (12.0)
L_SQLFMT: String (16.0)
L_CFORMAT: String (16.0)
R_REFADDR: Integer (10.0)
R_NREFADDR: Integer (10.0)
R_SQLNUMF: String (12.0)
R_SQLFMT: String (16.0)
R_CFORMAT: String (16.0)
L_AC5: String (35.0)
L_AC4: String (35.0)
L_AC3: String (35.0)
L_AC2: String (35.0)
L_AC1: String (35.0)
R_AC5: String (35.0)
R_AC4: String (35.0)
R_AC3: String (35.0)
R_AC2: String (35.0)
R_AC1: String (35.0)
L_POSTCODE: String (11.0)
R_POSTCODE: String (11.0)
MTFCC: Integer (5.0)
PASSFLG: String (1.0)
DIVROAD: String (1.0)
OGRFeature(Streets):0
   LINK_ID (Integer) = 40037470
   NAME (String) = I- 90
   L_REFADDR (Integer) = 0
   L_NREFADDR (Integer) = 0
   L_SQLNUMF (String) = (null)
   L_SQLFMT (String) = (null)
   L_CFORMAT (String) = (null)
   R_REFADDR (Integer) = 0
   R_NREFADDR (Integer) = 0
   R_SQLNUMF (String) = (null)
   R_SQLFMT (String) = (null)
   R_CFORMAT (String) = (null)
   L_AC5 (String) = (null)
   L_AC4 (String) = (null)
   L_AC3 (String) = Middlesex
   L_AC2 (String) = MA
   L_AC1 (String) = US
   R_AC5 (String) = (null)
   R_AC4 (String) = Hopkinton
   R_AC3 (String) = Middlesex
   R_AC2 (String) = MA
   R_AC1 (String) = US
   L_POSTCODE (String) = (null)
   R_POSTCODE (String) = (null)
   MTFCC (Integer) = 1100
   PASSFLG (String) = (null)
   DIVROAD (String) = Y
   LINESTRING (-71.563116999999991 
42.267372999999999,-71.563024999999996 42.267412999999998,-71.562956 
42.267443)

...