More fixes to layout. The compute neighbors function for horizontal lines is only intended to find neighbors on differing lines. However, it's entirely possible that horizontal neighbors could appear.

This commit finds horizontal neighbors in a horizonal line and merges them together into a single horizontal line if necessary.  This leads to much better text extraction  if the PDF was created in a funky way.

For example (test case coming), I have seen PDFs which are written almost like vertical columns, but the text is entirely horizontal.

pdfminer/layout.py

@@ -1,4 +1,5 @@
 #!/usr/bin/env python
+import logging
 from .utils import INF
 from .utils import Plane
 from .utils import get_bound
@@ -355,6 +356,9 @@ class LTTextLine(LTTextContainer):
         LTContainer.add(self, LTAnno('\n'))
         return
 
+    def group_line_neighbors(self, objs, ratio):
+        return objs
+
     def find_neighbors(self, plane, ratio):
         raise NotImplementedError
 
@@ -383,14 +387,52 @@ class LTTextLineHorizontal(LTTextLine):
         LTTextLine.add(self, obj)
         return
 
+    def is_neighbor(self, obj, d, same_line = False):
+        # Horizontal lines can only connect with horizontal lines
+        if not isinstance(obj, LTTextLineHorizontal):
+            return False
+        # Ensure they are vertically close
+        if abs(obj.height-self.height) >= d:
+            return False
+        # Ensure that they have similar start or stop x positions
+        if not (abs(obj.x0-self.x0) < d or
+                abs(obj.x1-self.x1) < d or 
+            # Or that they intersect eachother horizontally.
+                (obj.x0 < self.x0 and obj.x1 > self.x0) or
+                (obj.x0 > self.x0 and obj.x0 < self.x1)):
+            return False
+        if same_line and not (
+            # Ensure they have similar 
+                (obj.y0 == self.y0) or (obj.y1 == self.y1) or
+                (obj.y0 < self.y0 and obj.y0 > self.y1) or
+                (obj.y0 > self.y0 and obj.y1 < self.y0)):
+            return False
+        return True
+        
+    def group_line_neighbors(self, objs, ratio):
+        '''
+        Given a set of objects that may or may not be on the same line as this,
+        add the objects that are on the same line.
+        
+        Return the objects that are not on the same line.
+        '''
+        d = ratio*self.height
+        other_lines = []
+        for o in objs:
+            if o == self:
+                other_lines.append(o)
+            elif self.is_neighbor(o, d, same_line=True):
+                [self.add(oc) for oc in o]
+                # Clear out the old line
+                o._objs = []
+            else:
+                other_lines.append(o)
+        return other_lines
+    
     def find_neighbors(self, plane, ratio):
         d = ratio*self.height
         objs = plane.find((self.x0, self.y0-d, self.x1, self.y1+d))
-        return [obj for obj in objs
+        return [o for o in objs if self.is_neighbor(o, d)]
-                if (isinstance(obj, LTTextLineHorizontal) and
-                    abs(obj.height-self.height) < d and
-                    (abs(obj.x0-self.x0) < d or
-                     abs(obj.x1-self.x1) < d))]
 
 
 class LTTextLineVertical(LTTextLine):
@@ -577,19 +619,25 @@ class LTLayoutContainer(LTContainer):
         yield line
         return
 
-    # group_textlines: group neighboring lines to textboxes.
+    # group_textlines: group neighbouring lines to textboxes.
     def group_textlines(self, laparams, lines):
         plane = Plane(self.bbox)
         plane.extend(lines)
         boxes = {}
+        # for line in plane:
+            # print "line", ("".join([s._text for s in line])).encode('ascii', 'ignore')
         for line in lines:
             neighbors = line.find_neighbors(plane, laparams.line_margin)
-            if line not in neighbors: continue
+            if line not in neighbors: 
+                logging.error("Line cannot find itself: %s"%line)
+                continue
+            neighbors = line.group_line_neighbors(neighbors, laparams.line_margin)
             members = []
             for obj1 in neighbors:
                 members.append(obj1)
                 if obj1 in boxes:
                     members.extend(boxes.pop(obj1))
+            # print "members: ", ["".join([o._text for o in line]) for line in members]
             if isinstance(line, LTTextLineHorizontal):
                 box = LTTextBoxHorizontal()
             else: