def test_queryengine_io(self, fn):
        skip_if_no_external("h5py")
        from mvpa2.base.hdf5 import h5save, h5load

        vol_shape = (10, 10, 10, 1)
        vol_affine = np.identity(4)
        vg = volgeom.VolGeom(vol_shape, vol_affine)

        # generate some surfaces,
        # and add some noise to them
        sphere_density = 10
        outer = surf.generate_sphere(sphere_density) * 5 + 8
        inner = surf.generate_sphere(sphere_density) * 3 + 8
        radius = 5.0

        add_fa = ["center_distances", "grey_matter_position"]
        qe = disc_surface_queryengine(radius, vg, inner, outer, add_fa=add_fa)
        ds = fmri_dataset(vg.get_masked_nifti_image())

        # the following is not really a strong requirement. XXX remove?
        assert_raises(ValueError, lambda: qe[qe.ids[0]])

        # check that after training it behaves well
        qe.train(ds)
        i = qe.ids[0]
        try:
            m = qe[i]
        except ValueError, e:
            raise AssertionError(
                "Failed to query %r from %r after training on %r. " "Exception was: %r" % (i, qe, ds, e)
            )
Ejemplo n.º 2
0
    def test_queryengine_io(self, fn):
        skip_if_no_external('h5py')
        from mvpa2.base.hdf5 import h5save, h5load

        vol_shape = (10, 10, 10, 1)
        vol_affine = np.identity(4)
        vg = volgeom.VolGeom(vol_shape, vol_affine)

        # generate some surfaces,
        # and add some noise to them
        sphere_density = 10
        outer = surf.generate_sphere(sphere_density) * 5 + 8
        inner = surf.generate_sphere(sphere_density) * 3 + 8
        radius = 5.

        add_fa = ['center_distances', 'grey_matter_position']
        qe = disc_surface_queryengine(radius, vg, inner, outer, add_fa=add_fa)
        ds = fmri_dataset(vg.get_masked_nifti_image())

        # the following is not really a strong requirement. XXX remove?
        assert_raises(ValueError, lambda: qe[qe.ids[0]])

        # check that after training it behaves well
        qe.train(ds)
        i = qe.ids[0]
        try:
            m = qe[i]
        except ValueError, e:
            raise AssertionError(
                'Failed to query %r from %r after training on %r. Exception was: %r'
                % (i, qe, ds, e))
Ejemplo n.º 3
0
    def test_surface_minimal_voxel_selection(self):
        # Tests 'minimal' voxel selection.
        # It assumes that 'maximal' voxel selection works (which is tested
        # in other unit tests)
        vol_shape = (10, 10, 10, 1)
        vol_affine = np.identity(4)
        vg = volgeom.VolGeom(vol_shape, vol_affine)

        # generate some surfaces,
        # and add some noise to them
        sphere_density = 10
        nvertices = sphere_density**2 + 2
        noise = np.random.uniform(size=(nvertices, 3))
        outer = surf.generate_sphere(sphere_density) * 5 + 8 + noise
        inner = surf.generate_sphere(sphere_density) * 3 + 8 + noise

        radii = [5., 20., 10]  # note: no fixed radii at the moment

        # Note: a little outside margin is necessary
        # as otherwise there are nodes in the minimal case
        # that have no voxels associated with them

        for radius in radii:
            for output_modality in ('surface', 'volume'):
                for i, nvm in enumerate(('minimal', 'maximal')):
                    qe = disc_surface_queryengine(
                        radius,
                        vg,
                        inner,
                        outer,
                        node_voxel_mapping=nvm,
                        output_modality=output_modality)
                    voxsel = qe.voxsel

                    if i == 0:
                        keys_ = voxsel.keys()
                        voxsel_ = voxsel
                    else:
                        keys = voxsel.keys()
                        # minimal one has a subset
                        assert_equal(keys, keys_)

                        # and the subset is quite overlapping
                        assert_true(len(keys) * .90 < len(keys_))

                        for k in keys_:
                            x = set(voxsel_[k])
                            y = set(voxsel[k])

                            d = set.symmetric_difference(x, y)
                            r = float(len(d)) / 2 / len(x)
                            if type(radius) is float:
                                assert_equal(x - y, set())

                            # decent agreement in any case
                            # between the two sets
                            assert_true(r < .6)
    def test_surface_minimal_voxel_selection(self):
        # Tests 'minimal' voxel selection.
        # It assumes that 'maximal' voxel selection works (which is tested
        # in other unit tests)
        vol_shape = (10, 10, 10, 1)
        vol_affine = np.identity(4)
        vg = volgeom.VolGeom(vol_shape, vol_affine)

        # generate some surfaces,
        # and add some noise to them
        sphere_density = 10
        nvertices = sphere_density ** 2 + 2
        noise = np.random.uniform(size=(nvertices, 3))
        outer = surf.generate_sphere(sphere_density) * 5 + 8 + noise
        inner = surf.generate_sphere(sphere_density) * 3 + 8 + noise

        radii = [5.0, 20.0, 10]  # note: no fixed radii at the moment

        # Note: a little outside margin is necessary
        # as otherwise there are nodes in the minimal case
        # that have no voxels associated with them

        for radius in radii:
            for output_modality in ("surface", "volume"):
                for i, nvm in enumerate(("minimal", "maximal")):
                    qe = disc_surface_queryengine(
                        radius, vg, inner, outer, node_voxel_mapping=nvm, output_modality=output_modality
                    )
                    voxsel = qe.voxsel

                    if i == 0:
                        keys_ = voxsel.keys()
                        voxsel_ = voxsel
                    else:
                        keys = voxsel.keys()
                        # minimal one has a subset
                        assert_equal(keys, keys_)

                        # and the subset is quite overlapping
                        assert_true(len(keys) * 0.90 < len(keys_))

                        for k in keys_:
                            x = set(voxsel_[k])
                            y = set(voxsel[k])

                            d = set.symmetric_difference(x, y)
                            r = float(len(d)) / 2 / len(x)
                            if type(radius) is float:
                                assert_equal(x - y, set())

                            # decent agreement in any case
                            # between the two sets
                            assert_true(r < 0.6)
Ejemplo n.º 5
0
    def test_surface_minimal_lowres_voxel_selection(self, fn):
        vol_shape = (4, 10, 10, 1)
        vol_affine = np.identity(4)
        vg = volgeom.VolGeom(vol_shape, vol_affine)


        # make surfaces that are far away from all voxels
        # in the volume
        sphere_density = 10
        radius = 10

        outer = surf.generate_plane((0, 0, 4), (0, .4, 0),
                                    (0, 0, .4), 14, 14)
        inner = outer + 2

        source = surf.generate_plane((0, 0, 4), (0, .8, 0),
                                     (0, 0, .8), 7, 7) + 1

        for i, nvm in enumerate(('minimal', 'minimal_lowres')):
            qe = disc_surface_queryengine(radius, vg, inner,
                                          outer, source,
                                          node_voxel_mapping=nvm)

            voxsel = qe.voxsel
            if i == 0:
                voxsel0 = voxsel
            else:
                assert_equal(voxsel.keys(), voxsel0.keys())
                for k in voxsel.keys():
                    p = voxsel[k]
                    q = voxsel0[k]

                    # require at least 60% agreement
                    delta = set.symmetric_difference(set(p), set(q))
                    assert_true(len(delta) < .8 * (len(p) + len(q)))

            if externals.exists('h5py'):
                from mvpa2.base.hdf5 import h5save, h5load

                h5save(fn, voxsel)
                voxsel_copy = h5load(fn)
                assert_equal(voxsel.keys(), voxsel_copy.keys())

                for id in qe.ids:
                    assert_array_equal(voxsel.get(id),
                                       voxsel_copy.get(id))
Ejemplo n.º 6
0
    def test_surface_minimal_lowres_voxel_selection(self, fn):
        vol_shape = (4, 10, 10, 1)
        vol_affine = np.identity(4)
        vg = volgeom.VolGeom(vol_shape, vol_affine)

        # make surfaces that are far away from all voxels
        # in the volume
        sphere_density = 10
        radius = 10

        outer = surf.generate_plane((0, 0, 4), (0, .4, 0), (0, 0, .4), 14, 14)
        inner = outer + 2

        source = surf.generate_plane((0, 0, 4), (0, .8, 0),
                                     (0, 0, .8), 7, 7) + 1

        for i, nvm in enumerate(('minimal', 'minimal_lowres')):
            qe = disc_surface_queryengine(radius,
                                          vg,
                                          inner,
                                          outer,
                                          source,
                                          node_voxel_mapping=nvm)

            voxsel = qe.voxsel
            if i == 0:
                voxsel0 = voxsel
            else:
                assert_equal(voxsel.keys(), voxsel0.keys())
                for k in voxsel.keys():
                    p = voxsel[k]
                    q = voxsel0[k]

                    # require at least 60% agreement
                    delta = set.symmetric_difference(set(p), set(q))
                    assert_true(len(delta) < .8 * (len(p) + len(q)))

            if externals.exists('h5py'):
                from mvpa2.base.hdf5 import h5save, h5load

                h5save(fn, voxsel)
                voxsel_copy = h5load(fn)
                assert_equal(voxsel.keys(), voxsel_copy.keys())

                for id in qe.ids:
                    assert_array_equal(voxsel.get(id), voxsel_copy.get(id))
    def test_voxel_selection(self):
        """Compare surface and volume based searchlight"""

        """
        Tests to see whether results are identical for surface-based
        searchlight (just one plane; Euclidean distnace) and volume-based
        searchlight.

        Note that the current value is a float; if it were int, it would
        specify the number of voxels in each searchlight"""

        radius = 10.0

        """Define input filenames"""
        epi_fn = pathjoin(pymvpa_dataroot, "bold.nii.gz")
        maskfn = pathjoin(pymvpa_dataroot, "mask.nii.gz")

        """
        Use the EPI datafile to define a surface.
        The surface has as many nodes as there are voxels
        and is parallel to the volume 'slice'
        """
        vg = volgeom.from_any(maskfn, mask_volume=True)

        aff = vg.affine
        nx, ny, nz = vg.shape[:3]

        """Plane goes in x and y direction, so we take these vectors
        from the affine transformation matrix of the volume"""
        plane = surf.generate_plane(aff[:3, 3], aff[:3, 0], aff[:3, 1], nx, ny)

        """
        Simulate pial and white matter as just above and below
        the central plane
        """
        normal_vec = aff[:3, 2]
        outer = plane + normal_vec
        inner = plane + -normal_vec

        """
        Combine volume and surface information
        """
        vsm = volsurf.VolSurfMaximalMapping(vg, outer, inner)

        """
        Run voxel selection with specified radius (in mm), using
        Euclidean distance measure
        """
        surf_voxsel = surf_voxel_selection.voxel_selection(vsm, radius, distance_metric="e")

        """Define the measure"""

        # run_slow=True would give an actual cross-validation with meaningful
        # accuracies. Because this is a unit-test only the number of voxels
        # in each searchlight is tested.
        run_slow = False

        if run_slow:
            meas = CrossValidation(GNB(), OddEvenPartitioner(), errorfx=lambda p, t: np.mean(p == t))
            postproc = mean_sample
        else:
            meas = _Voxel_Count_Measure()
            postproc = lambda x: x

        """
        Surface analysis: define the query engine, cross validation,
        and searchlight
        """
        surf_qe = SurfaceVerticesQueryEngine(surf_voxsel)
        surf_sl = Searchlight(meas, queryengine=surf_qe, postproc=postproc)

        """
        new (Sep 2012): also test 'simple' queryengine wrapper function
        """

        surf_qe2 = disc_surface_queryengine(
            radius, maskfn, inner, outer, plane, volume_mask=True, distance_metric="euclidean"
        )
        surf_sl2 = Searchlight(meas, queryengine=surf_qe2, postproc=postproc)

        """
        Same for the volume analysis
        """
        element_sizes = tuple(map(abs, (aff[0, 0], aff[1, 1], aff[2, 2])))
        sph = Sphere(radius, element_sizes=element_sizes)
        kwa = {"voxel_indices": sph}

        vol_qe = IndexQueryEngine(**kwa)
        vol_sl = Searchlight(meas, queryengine=vol_qe, postproc=postproc)

        """The following steps are similar to start_easy.py"""
        attr = SampleAttributes(pathjoin(pymvpa_dataroot, "attributes_literal.txt"))

        mask = surf_voxsel.get_mask()

        dataset = fmri_dataset(
            samples=pathjoin(pymvpa_dataroot, "bold.nii.gz"), targets=attr.targets, chunks=attr.chunks, mask=mask
        )

        if run_slow:
            # do chunkswise linear detrending on dataset

            poly_detrend(dataset, polyord=1, chunks_attr="chunks")

            # zscore dataset relative to baseline ('rest') mean
            zscore(dataset, chunks_attr="chunks", param_est=("targets", ["rest"]))

        # select class face and house for this demo analysis
        # would work with full datasets (just a little slower)
        dataset = dataset[np.array([l in ["face", "house"] for l in dataset.sa.targets], dtype="bool")]

        """Apply searchlight to datasets"""
        surf_dset = surf_sl(dataset)
        surf_dset2 = surf_sl2(dataset)
        vol_dset = vol_sl(dataset)

        surf_data = surf_dset.samples
        surf_data2 = surf_dset2.samples
        vol_data = vol_dset.samples

        assert_array_equal(surf_data, surf_data2)
        assert_array_equal(surf_data, vol_data)
    def test_voxel_selection_alternative_calls(self):
        # Tests a multitude of different searchlight calls
        # that all should yield exactly the same results.
        #
        # Calls differ by whether the arguments are filenames
        # or data objects, whether values are specified explicityly
        # or set to the default implicitly (using None).
        # and by different calls to run the voxel selection.
        #
        # This method does not test for mask functionality.

        # define the volume
        vol_shape = (10, 10, 10, 3)
        vol_affine = np.identity(4)
        vol_affine[0, 0] = vol_affine[1, 1] = vol_affine[2, 2] = 5

        # four versions: array, nifti image, file name, fmri dataset
        volarr = np.ones(vol_shape)
        volimg = nb.Nifti1Image(volarr, vol_affine)
        # There is a detected problem with elderly NumPy's (e.g. 1.6.1
        # on precise on travis) leading to segfaults while operating
        # on memmapped volumes being forwarded to pprocess.
        # Thus just making it compressed volume for those cases
        suf = ".gz" if (externals.exists("pprocess") and externals.versions["numpy"] < "1.6.2") else ""
        fd, volfn = tempfile.mkstemp("vol.nii" + suf, "test")
        os.close(fd)
        volimg.to_filename(volfn)
        volds = fmri_dataset(volfn)

        fd, volfngz = tempfile.mkstemp("vol.nii.gz", "test")
        os.close(fd)
        volimg.to_filename(volfngz)
        voldsgz = fmri_dataset(volfngz)

        # make the surfaces
        sphere_density = 10

        # two versions: Surface and file name
        outer = surf.generate_sphere(sphere_density) * 25.0 + 15
        inner = surf.generate_sphere(sphere_density) * 20.0 + 15
        intermediate = inner * 0.5 + outer * 0.5
        nv = outer.nvertices

        fd, outerfn = tempfile.mkstemp("outer.asc", "test")
        os.close(fd)
        fd, innerfn = tempfile.mkstemp("inner.asc", "test")
        os.close(fd)
        fd, intermediatefn = tempfile.mkstemp("intermediate.asc", "test")
        os.close(fd)

        for s, fn in zip([outer, inner, intermediate], [outerfn, innerfn, intermediatefn]):
            surf.write(fn, s, overwrite=True)

        # searchlight radius (in mm)
        radius = 10.0

        # dataset used to run searchlight on
        ds = fmri_dataset(volfn)

        # simple voxel counter (run for each searchlight position)
        m = _Voxel_Count_Measure()

        # number of voxels expected in each searchlight
        r_expected = np.array(
            [
                [
                    18,
                    9,
                    10,
                    9,
                    9,
                    9,
                    9,
                    10,
                    9,
                    9,
                    9,
                    9,
                    11,
                    11,
                    11,
                    11,
                    10,
                    10,
                    10,
                    9,
                    10,
                    11,
                    9,
                    10,
                    10,
                    8,
                    7,
                    8,
                    8,
                    8,
                    9,
                    10,
                    12,
                    12,
                    11,
                    7,
                    7,
                    8,
                    5,
                    9,
                    11,
                    11,
                    12,
                    12,
                    9,
                    5,
                    8,
                    7,
                    7,
                    12,
                    12,
                    13,
                    12,
                    12,
                    7,
                    7,
                    8,
                    5,
                    9,
                    12,
                    12,
                    13,
                    11,
                    9,
                    5,
                    8,
                    7,
                    7,
                    11,
                    12,
                    12,
                    11,
                    12,
                    10,
                    10,
                    11,
                    9,
                    11,
                    12,
                    12,
                    12,
                    12,
                    16,
                    13,
                    16,
                    16,
                    16,
                    17,
                    15,
                    17,
                    17,
                    17,
                    16,
                    16,
                    16,
                    18,
                    16,
                    16,
                    16,
                    16,
                    18,
                    16,
                ]
            ]
        )

        params = dict(
            intermediate_=(intermediate, intermediatefn, None),
            center_nodes_=(None, range(nv)),
            volume_=(volimg, volfn, volds, volfngz, voldsgz),
            surf_src_=("filename", "surf"),
            volume_mask_=(None, True, 0, 2),
            call_method_=("qe", "rvs", "gam"),
        )

        combis = _cartprod(params)  # compute all possible combinations
        combistep = 17  # 173
        # some fine prime number to speed things up
        # if this value becomes too big then not all
        # cases are covered
        # the unit test tests itself whether all values
        # occur at least once

        tested_params = dict()

        def val2str(x):
            return "%r:%r" % (type(x), x)

        for i in xrange(0, len(combis), combistep):
            combi = combis[i]

            intermediate_ = combi["intermediate_"]
            center_nodes_ = combi["center_nodes_"]
            volume_ = combi["volume_"]
            surf_src_ = combi["surf_src_"]
            volume_mask_ = combi["volume_mask_"]
            call_method_ = combi["call_method_"]

            # keep track of which values were used -
            # so that this unit test tests itself

            for k in combi.keys():
                if not k in tested_params:
                    tested_params[k] = set()
                tested_params[k].add(val2str(combi[k]))

            if surf_src_ == "filename":
                s_i, s_m, s_o = inner, intermediate, outer
            elif surf_src_ == "surf":
                s_i, s_m, s_o = innerfn, intermediatefn, outerfn
            else:
                raise ValueError("this should not happen")

            if call_method_ == "qe":
                # use the fancy query engine wrapper
                qe = disc_surface_queryengine(
                    radius, volume_, s_i, s_o, s_m, source_surf_nodes=center_nodes_, volume_mask=volume_mask_
                )
                sl = Searchlight(m, queryengine=qe)
                r = sl(ds).samples

            elif call_method_ == "rvs":
                # use query-engine but build the
                # ingredients by hand
                vg = volgeom.from_any(volume_, volume_mask_)
                vs = volsurf.VolSurfMaximalMapping(vg, s_i, s_o)
                sel = surf_voxel_selection.voxel_selection(vs, radius, source_surf=s_m, source_surf_nodes=center_nodes_)
                qe = SurfaceVerticesQueryEngine(sel)
                sl = Searchlight(m, queryengine=qe)
                r = sl(ds).samples

            elif call_method_ == "gam":
                # build everything from the ground up
                vg = volgeom.from_any(volume_, volume_mask_)
                vs = volsurf.VolSurfMaximalMapping(vg, s_i, s_o)
                sel = surf_voxel_selection.voxel_selection(vs, radius, source_surf=s_m, source_surf_nodes=center_nodes_)
                mp = sel

                ks = sel.keys()
                nk = len(ks)
                r = np.zeros((1, nk))
                for i, k in enumerate(ks):
                    r[0, i] = len(mp[k])

            # check if result is as expected
            assert_array_equal(r_expected, r)

        # clean up
        all_fns = [volfn, volfngz, outerfn, innerfn, intermediatefn]
        map(os.remove, all_fns)

        for k, vs in params.iteritems():
            if not k in tested_params:
                raise ValueError("Missing key: %r" % k)
            for v in vs:
                vstr = val2str(v)
                if not vstr in tested_params[k]:
                    raise ValueError("Missing value %r for %s" % (tested_params[k], k))
Ejemplo n.º 9
0
    def test_voxel_selection(self):
        '''Compare surface and volume based searchlight'''
        '''
        Tests to see whether results are identical for surface-based
        searchlight (just one plane; Euclidean distnace) and volume-based
        searchlight.

        Note that the current value is a float; if it were int, it would
        specify the number of voxels in each searchlight'''

        radius = 10.
        '''Define input filenames'''
        epi_fn = os.path.join(pymvpa_dataroot, 'bold.nii.gz')
        maskfn = os.path.join(pymvpa_dataroot, 'mask.nii.gz')
        '''
        Use the EPI datafile to define a surface.
        The surface has as many nodes as there are voxels
        and is parallel to the volume 'slice'
        '''
        vg = volgeom.from_any(maskfn, mask_volume=True)

        aff = vg.affine
        nx, ny, nz = vg.shape[:3]
        '''Plane goes in x and y direction, so we take these vectors
        from the affine transformation matrix of the volume'''
        plane = surf.generate_plane(aff[:3, 3], aff[:3, 0], aff[:3, 1], nx, ny)
        '''
        Simulate pial and white matter as just above and below
        the central plane
        '''
        normal_vec = aff[:3, 2]
        outer = plane + normal_vec
        inner = plane + -normal_vec
        '''
        Combine volume and surface information
        '''
        vsm = volsurf.VolSurfMaximalMapping(vg, outer, inner)
        '''
        Run voxel selection with specified radius (in mm), using
        Euclidean distance measure
        '''
        surf_voxsel = surf_voxel_selection.voxel_selection(vsm,
                                                           radius,
                                                           distance_metric='e')
        '''Define the measure'''

        # run_slow=True would give an actual cross-validation with meaningful
        # accuracies. Because this is a unit-test only the number of voxels
        # in each searchlight is tested.
        run_slow = False

        if run_slow:
            meas = CrossValidation(GNB(),
                                   OddEvenPartitioner(),
                                   errorfx=lambda p, t: np.mean(p == t))
            postproc = mean_sample
        else:
            meas = _Voxel_Count_Measure()
            postproc = lambda x: x
        '''
        Surface analysis: define the query engine, cross validation,
        and searchlight
        '''
        surf_qe = SurfaceVerticesQueryEngine(surf_voxsel)
        surf_sl = Searchlight(meas, queryengine=surf_qe, postproc=postproc)
        '''
        new (Sep 2012): also test 'simple' queryengine wrapper function
        '''

        surf_qe2 = disc_surface_queryengine(radius,
                                            maskfn,
                                            inner,
                                            outer,
                                            plane,
                                            volume_mask=True,
                                            distance_metric='euclidean')
        surf_sl2 = Searchlight(meas, queryengine=surf_qe2, postproc=postproc)
        '''
        Same for the volume analysis
        '''
        element_sizes = tuple(map(abs, (aff[0, 0], aff[1, 1], aff[2, 2])))
        sph = Sphere(radius, element_sizes=element_sizes)
        kwa = {'voxel_indices': sph}

        vol_qe = IndexQueryEngine(**kwa)
        vol_sl = Searchlight(meas, queryengine=vol_qe, postproc=postproc)
        '''The following steps are similar to start_easy.py'''
        attr = SampleAttributes(
            os.path.join(pymvpa_dataroot, 'attributes_literal.txt'))

        mask = surf_voxsel.get_mask()

        dataset = fmri_dataset(samples=os.path.join(pymvpa_dataroot,
                                                    'bold.nii.gz'),
                               targets=attr.targets,
                               chunks=attr.chunks,
                               mask=mask)

        if run_slow:
            # do chunkswise linear detrending on dataset

            poly_detrend(dataset, polyord=1, chunks_attr='chunks')

            # zscore dataset relative to baseline ('rest') mean
            zscore(dataset,
                   chunks_attr='chunks',
                   param_est=('targets', ['rest']))

        # select class face and house for this demo analysis
        # would work with full datasets (just a little slower)
        dataset = dataset[np.array(
            [l in ['face', 'house'] for l in dataset.sa.targets],
            dtype='bool')]
        '''Apply searchlight to datasets'''
        surf_dset = surf_sl(dataset)
        surf_dset2 = surf_sl2(dataset)
        vol_dset = vol_sl(dataset)

        surf_data = surf_dset.samples
        surf_data2 = surf_dset2.samples
        vol_data = vol_dset.samples

        assert_array_equal(surf_data, surf_data2)
        assert_array_equal(surf_data, vol_data)
Ejemplo n.º 10
0
    def test_voxel_selection_alternative_calls(self):
        # Tests a multitude of different searchlight calls
        # that all should yield exactly the same results.
        #
        # Calls differ by whether the arguments are filenames
        # or data objects, whether values are specified explicityly
        # or set to the default implicitly (using None).
        # and by different calls to run the voxel selection.
        #
        # This method does not test for mask functionality.

        # define the volume
        vol_shape = (10, 10, 10, 3)
        vol_affine = np.identity(4)
        vol_affine[0, 0] = vol_affine[1, 1] = vol_affine[2, 2] = 5

        # four versions: array, nifti image, file name, fmri dataset
        volarr = np.ones(vol_shape)
        volimg = nb.Nifti1Image(volarr, vol_affine)
        # There is a detected problem with elderly NumPy's (e.g. 1.6.1
        # on precise on travis) leading to segfaults while operating
        # on memmapped volumes being forwarded to pprocess.
        # Thus just making it compressed volume for those cases
        suf = '.gz' \
            if externals.exists('pprocess') and externals.versions['numpy'] < '1.6.2' \
            else ''
        fd, volfn = tempfile.mkstemp('vol.nii' + suf, 'test')
        os.close(fd)
        volimg.to_filename(volfn)
        volds = fmri_dataset(volfn)

        fd, volfngz = tempfile.mkstemp('vol.nii.gz', 'test')
        os.close(fd)
        volimg.to_filename(volfngz)
        voldsgz = fmri_dataset(volfngz)

        # make the surfaces
        sphere_density = 10

        # two versions: Surface and file name
        outer = surf.generate_sphere(sphere_density) * 25. + 15
        inner = surf.generate_sphere(sphere_density) * 20. + 15
        intermediate = inner * .5 + outer * .5
        nv = outer.nvertices

        fd, outerfn = tempfile.mkstemp('outer.asc', 'test')
        os.close(fd)
        fd, innerfn = tempfile.mkstemp('inner.asc', 'test')
        os.close(fd)
        fd, intermediatefn = tempfile.mkstemp('intermediate.asc', 'test')
        os.close(fd)

        for s, fn in zip([outer, inner, intermediate],
                         [outerfn, innerfn, intermediatefn]):
            surf.write(fn, s, overwrite=True)

        # searchlight radius (in mm)
        radius = 10.

        # dataset used to run searchlight on
        ds = fmri_dataset(volfn)

        # simple voxel counter (run for each searchlight position)
        m = _Voxel_Count_Measure()

        # number of voxels expected in each searchlight
        r_expected = np.array([[
            18, 9, 10, 9, 9, 9, 9, 10, 9, 9, 9, 9, 11, 11, 11, 11, 10, 10, 10,
            9, 10, 11, 9, 10, 10, 8, 7, 8, 8, 8, 9, 10, 12, 12, 11, 7, 7, 8, 5,
            9, 11, 11, 12, 12, 9, 5, 8, 7, 7, 12, 12, 13, 12, 12, 7, 7, 8, 5,
            9, 12, 12, 13, 11, 9, 5, 8, 7, 7, 11, 12, 12, 11, 12, 10, 10, 11,
            9, 11, 12, 12, 12, 12, 16, 13, 16, 16, 16, 17, 15, 17, 17, 17, 16,
            16, 16, 18, 16, 16, 16, 16, 18, 16
        ]])

        params = dict(intermediate_=(intermediate, intermediatefn, None),
                      center_nodes_=(None, range(nv)),
                      volume_=(volimg, volfn, volds, volfngz, voldsgz),
                      surf_src_=('filename', 'surf'),
                      volume_mask_=(None, True, 0, 2),
                      call_method_=("qe", "rvs", "gam"))

        combis = _cartprod(params)  # compute all possible combinations
        combistep = 17  #173
        # some fine prime number to speed things up
        # if this value becomes too big then not all
        # cases are covered
        # the unit test tests itself whether all values
        # occur at least once

        tested_params = dict()

        def val2str(x):
            return '%r:%r' % (type(x), x)

        for i in xrange(0, len(combis), combistep):
            combi = combis[i]

            intermediate_ = combi['intermediate_']
            center_nodes_ = combi['center_nodes_']
            volume_ = combi['volume_']
            surf_src_ = combi['surf_src_']
            volume_mask_ = combi['volume_mask_']
            call_method_ = combi['call_method_']

            # keep track of which values were used -
            # so that this unit test tests itself

            for k in combi.keys():
                if not k in tested_params:
                    tested_params[k] = set()
                tested_params[k].add(val2str(combi[k]))

            if surf_src_ == 'filename':
                s_i, s_m, s_o = inner, intermediate, outer
            elif surf_src_ == 'surf':
                s_i, s_m, s_o = innerfn, intermediatefn, outerfn
            else:
                raise ValueError('this should not happen')

            if call_method_ == "qe":
                # use the fancy query engine wrapper
                qe = disc_surface_queryengine(radius,
                                              volume_,
                                              s_i,
                                              s_o,
                                              s_m,
                                              source_surf_nodes=center_nodes_,
                                              volume_mask=volume_mask_)
                sl = Searchlight(m, queryengine=qe)
                r = sl(ds).samples

            elif call_method_ == 'rvs':
                # use query-engine but build the
                # ingredients by hand
                vg = volgeom.from_any(volume_, volume_mask_)
                vs = volsurf.VolSurfMaximalMapping(vg, s_i, s_o)
                sel = surf_voxel_selection.voxel_selection(
                    vs,
                    radius,
                    source_surf=s_m,
                    source_surf_nodes=center_nodes_)
                qe = SurfaceVerticesQueryEngine(sel)
                sl = Searchlight(m, queryengine=qe)
                r = sl(ds).samples

            elif call_method_ == 'gam':
                # build everything from the ground up
                vg = volgeom.from_any(volume_, volume_mask_)
                vs = volsurf.VolSurfMaximalMapping(vg, s_i, s_o)
                sel = surf_voxel_selection.voxel_selection(
                    vs,
                    radius,
                    source_surf=s_m,
                    source_surf_nodes=center_nodes_)
                mp = sel

                ks = sel.keys()
                nk = len(ks)
                r = np.zeros((1, nk))
                for i, k in enumerate(ks):
                    r[0, i] = len(mp[k])

            # check if result is as expected
            assert_array_equal(r_expected, r)

        # clean up
        all_fns = [volfn, volfngz, outerfn, innerfn, intermediatefn]
        map(os.remove, all_fns)

        for k, vs in params.iteritems():
            if not k in tested_params:
                raise ValueError("Missing key: %r" % k)
            for v in vs:
                vstr = val2str(v)
                if not vstr in tested_params[k]:
                    raise ValueError("Missing value %r for %s" %
                                     (tested_params[k], k))