GDALPolygonize doesn't vectorize all pixels C++

[sghofrany]

Expected behavior and actual behavior.

I expect the GDALPolygonize function to take in a raster file and return a vector file that covers all of the pixels in the input.

Steps to reproduce the problem.

Here is the high level of what I am doing:

1. Read in raster file.
2. Create a vector layer to pass into GDALPolygonize.
3. Call GDALPolygonize with raster band from input and the vector layer created.

Here is the code I am running:

    
   string strPath = "chunked_test_chunk_16.tif";

    auto *dataset = (GDALDataset*) GDALOpen(strPath.c_str(), GA_ReadOnly);

    if(dataset == nullptr) {
        return;
    }

    const char *pszDriverName{"GPKG"};
    GDALDriver *poDriver{GetGDALDriverManager()->GetDriverByName(pszDriverName)};

    GDALDataset *polygonized = poDriver->Create((string(filePath.stem()) + ".gpkg").c_str(), 0, 0, 0, GDT_Unknown, nullptr);

    char *cWkt = nullptr;
    dataset->GetSpatialRef()->exportToWkt(&cWkt);

    OGRSpatialReference spatialReference;
    spatialReference.importFromWkt(cWkt);

    OGRwkbGeometryType geomType = wkbPolygon;
    OGRLayer *tmpLayer = polygonized->CreateLayer("polygon", &spatialReference, geomType);

    if(tmpLayer == nullptr) {
        throw std::invalid_argument("Could not create layer");
    }

    OGRFieldDefn field("CellValue", OFTInteger);
    tmpLayer->CreateField(&field);

    GDALRasterBand *rasterBand = dataset->GetRasterBand(1);

    GDALPolygonize(rasterBand, rasterBand, tmpLayer, 0, nullptr, nullptr, nullptr);
    tmpLayer->SyncToDisk();
    
    GDALClose(dataset);
    GDALClose(polygonized);

I have attached the raster file I used and the output file I get from running the above code. GitHub doesn't allow me to upload .tif files, so I have added it in a zip file.

The picture below is what I see in QGIS. The pink color is the polygons and the black is the raster representation. As you can see there the black pixels were not polygonized.

Operating system

WSL2
Ubuntu 20.04.2 LTS

GDAL version and provenance

GDAL 3.5.3, released 2022/10/21
chunked_test_chunk_16.zip

[rouault]

The reason is that you pass the rasterBand itself as the value for the maskBand argument of GDALPolygonize(), which cause pixels at 0 to be considered invalid.
Try rather

GDALPolygonize(rasterBand, rasterBand->GetMaskBand(), tmpLayer, 0, nullptr, nullptr, nullptr);

[sghofrany]

The reason is that you pass the rasterBand itself as the value for the maskBand argument of GDALPolygonize(), which cause pixels at 0 to be considered invalid. Try rather

GDALPolygonize(rasterBand, rasterBand->GetMaskBand(), tmpLayer, 0, nullptr, nullptr, nullptr);

I thought that passing the same raster band again would act as the mask band?

[rouault]

I thought that passing the same raster band again would act as the mask band?

nothing in the docs suggest so: https://gdal.org/api/gdal_alg.html#_CPPv414GDALPolygonize15GDALRasterBandH15GDALRasterBandH9OGRLayerHiPPc16GDALProgressFuncPv

[sghofrany]

I thought that passing the same raster band again would act as the mask band?

nothing in the docs suggest so: https://gdal.org/api/gdal_alg.html#_CPPv414GDALPolygonize15GDALRasterBandH15GDALRasterBandH9OGRLayerHiPPc16GDALProgressFuncPv

Fair point. I did test it and it does seem to be working on the small dataset I provided. Thanks for your help!