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I am new to GDAL in Python and would like to use it to create a list of populated layers in a ArcGIS mdb Feature datasets. I have the code below that provides a list of all the populated layers but it returns a list for all the datasets in the database. The database has Feature datasets for municipal water systems, sewer systems, transportation systems, etc. How can I return only the layer counts for one of these Feature datasets and all of its layers; i.e Feaure dataset = water_systems and returns layers of Water_lines, Fire_Hydrants, Water_Valves, etc.?

Thanks in advance.

import osgeo.ogr as ogr
driver = ogr.GetDriverByName('PGeo')
ds = driver.Open(database)
numLayers = ds.GetLayerCount()
for layerNum in range(numLayers):
    layer = ds.GetLayer(layerNum)
    if layer.GetFeatureCount() > 0:
        print '%s features: %s' % (layer.GetName(), layer.GetFeatureCount())

[Edit: Additional Info]

When running OGRINFO -al on the data base I get a lot of information but was able to pull out the following:

OGRFeature(GDB_Items):70
    ObjectID (Integer) = 70
    UUID (String) = DB50B2B0-9DC6-4492-9CAD-4162580231B6
    Type (String) = 70737809-852C-4A03-9E22-2CECEA5B9BFA
    Name (String) = WaterV
    PhysicalName (String) = WATERV
    Path (String) = \Water_Sys\WaterV
    DatasetSubtype1 (Integer) = 1
    DatasetInfo1 (String) = SHAPE
    ...

Further down the massive list was:

OGRFeature(GDB_Items):827
    ObjectID (Integer) = 827
    UUID (String) = 22CAD8B9-DBBE-44A6-9D8C-86896CC23B72
    Type (String) = 70737809-852C-4A03-9E22-2CECEA5B9BFA
    Name (String) = Signal_3
    PhysicalName (String) = SIGNAL_3
    Path (String) = \Trans\Signal_3
    DatasetSubtype1 (Integer) = 1
    DatasetInfo1 (String) = Shape
    ...

Note the Path parameter contains the ArcGIS Feature Dataset Name!!!

How can I read this using GDAL in Python?

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2 Answers

It is a little difficult to understand your problem without hearing what your code outputs.

I don't know if it is a cut and pase error or not, but I am guessing that you want to indent the last three lines of your code so that they get executed within the loop.

import osgeo.ogr as ogr
driver = ogr.GetDriverByName('PGeo')
ds = driver.Open(database)
numLayers = ds.GetLayerCount()
for layerNum in range(numLayers):
    layer = ds.GetLayer(layerNum)
    if layer.GetName() == "water_systems":
        print '%s features: %s' % (layer.GetName(), layer.GetFeatureCount())

I don't have a personal geodatabase handy to test with, but I think that this should work. It assumes that you know what the 'water systems' layer name is and in this case, I used "water_systems".

[EDIT] I think that this example should give you what you are looking for. Since you can't apparently namespace based on the feature dataset, you will need to create a list of the layers that you are interested in and then use that to determine which layers to get feature counts from.

import osgeo.ogr as ogr
database = 'test.mdb'
layerList = ['water_lines','water_valves','fire_hydrants']
driver = ogr.GetDriverByName('PGeo')
ds = driver.Open(database)
numLayers = ds.GetLayerCount()
for layerNum in range(numLayers):
    layer = ds.GetLayer(layerNum)
    if layer.GetName() in layerList:
        print '%s features: %s' % (layer.GetName(), layer.GetFeatureCount())

I think that part of the issue is that the 'personal geodatabase' format is a proprietary ESRI format and the OGR driver doesn't/can't fully access all of the metadata and interface with it as well as ESRI's proprietary tools.

[Another Edit]

OK, it isn't documented in the OGR PGeo driver page, but based on your information about the GDB_Items Layer, this should give you what you want, if you have the same feature data set name across all of the .mdb files.

import osgeo.ogr as ogr
database = 'test.mdb'
layerList = ['GDB_Items']
fdLayerList = []
goodPathString = "water_systems"
driver = ogr.GetDriverByName('PGeo')
ds = driver.Open(database)
numLayers = ds.GetLayerCount()
metaLayer = ds.GetLayerByName("GDB_Items")

feat = metaLayer.GetNextFeature()
while feat:
    fdLayerList.append(feat.path[len(goodPathString)+2:])
    feat = metaLayer.GetNextFeature()

for layerNum in range(numLayers):
    layer = ds.GetLayer(layerNum)
    if layer.GetName() in fdLayerList:
        print '%s features: %s' % (layer.GetName(), layer.GetFeatureCount())
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It sounds like you are saying that the data layers are in a ArcGIS feature dataset inside the PGeo. Correct? I am curious what kind of output you get if you just run the commandline ogrinfo against the db. That might help you figure out how to come up with a qualified name for the data layer. –  DavidF Nov 16 '12 at 20:17
    
I created a test .mdb file with some single feature classes/layers and some feature classes in a feature data set. When I loop through the layers, they are all listed, with no indication of whether they are included in a feature dataset or not. It also appears that layer names in a PGeo must be unique without taking the feature dataset name into account. I tried to create a second layer with the same name, outside of the feature dataset and got an error. So, I would just create a Python list of the layer names that you want and use that to pull out the data you are interested in. –  DavidF Nov 16 '12 at 21:18
2  
Despite having originally written the PGeo driver, I'm not all that familiar with geodatabase lingo. I'm assuming that "Feature dataset" is some sort of name for a schema or grouping to which layers can belong. Assuming this is the case it has no direct OGR analog and is not going to be directly exposed via OGR. This is likely to make it hard to utilize as a criteria. –  Frank Warmerdam Nov 17 '12 at 0:10
    
As Frank says, he literally wrote OGR/GDAL. GDAL == Frank. The OGR GDB_Items layer may have some metadata about the feature datasets and actual metadata on the data, but if you want to access the ogr layers, there is no namespacing for the feature dataset. –  DavidF Nov 17 '12 at 4:01
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As I understand it, you're saying your mdb has multiple tables (e.g., a table for "municipal water systems", a table for "sewer systems", etc), and you want to get the feature count for a specific table.

If that's the case, you can just get the feature count of the specific table (dataset/layer/etc) name that you want to look at.

if layer.GetName() == '<name of table in question>':
    count = layer.GetFeatureCount()
    table = layer.GetName()
    print 'There are %s features in %s' %(count, table)

Also, since you are new to GDAL in Python, you might find it useful to look at something like Fiona, which bills itself as "OGR's neater API". I have not used it much myself yet, but have read great things - and its documentation seems much friendlier than the default GDAL/OGR Python docs.

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Sorry, didn't refresh the page before posting. DavidF's answer is correct; I double-checked, this will work fine with mdbs –  sjs Nov 16 '12 at 18:07
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