Add example of plotting Freesurfer normalization

Author: mwaskom

examples/example_data/lh.curv.fsaverage.mgz

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+"""
+Plot Freesurfer Normalization
+=============================
+
+This example shows how PySurfer can be used to examine the quality of
+Freesurfer's curvature-driven normalization to a common template.
+
+We are going to plot the contour of the subject's curvature estimate after
+transforming that map into the common space (this step is performed outside
+of PySurfer using the Freesurfer program ``mri_surf2surf``).
+
+With a perfect transformation, the contour lines should follow the light/dark
+gray boundary on the fsaverage surface. Large deviations may reflect problems
+with the underlying data that you should investigate.
+
+"""
+import nibabel as nib
+from surfer import Brain
+
+brain = Brain("fsaverage", "both", "inflated")
+
+for hemi in ["lh", "rh"]:
+
+    # This file was created with mri_surf2surf
+    curv = nib.load("example_data/%s.curv.fsaverage.mgz" % hemi)
+
+    # Binarize the curvature at 0
+    curv_bin = (curv.get_data() > 0).squeeze()
+
+    # Add the data as a contour overlay, but turn off the colorbar
+    brain.add_contour_overlay(curv_bin, 0, 1.15, 2, 3, hemi=hemi)
+    brain.contour_list[-1]["colorbar"].visible = False
+
+brain.show_view("dorsal")