PolygonMatch™ is an optimal way to locate objects with sub-pixel accuracy independent of:

• scale
• rotation
• size
• perspective
• skew

Multiple polygons defines the shape or model of the object. Using the model the same shapes are extracted from the images and fitted to the original model with the highest possible accuracy. 

The versatility of PolygonMatch™ makes it suitable for a large number of applications:

• Robot Vision - pick and place
• 3D Stereo Vision
• Object Location
• Identification System

Below a valve which located using two polygons - a circle and a straight line. A model can consist of any number of polygons.

The tool is very powerful and can be used to locate an object of any size or shape with sub-pixel resolution.

The next example corrects the location of a printed circuit by 0.05 mm with accuracy better than 1/10 a pixel.

Other important application areas are shape verification.

Setup

Reference - Reference system selection

Trace lines

• Use Traceline Count - selects to specify the traceline count
  • Count - number of trace lines
  • Step length - distance between traceline
    • Ref coord
    • Pixels
• Start point - position of starting point on trace line given in reference coordinates
• End point - position of end point on trace line given in reference coordinates
  • Inverted the sign of start and stop point will change the direction of the trace comb
• Trace step (pixels) - normally 1 - given in pixels
• Line width (pixels) - 0 - trace line is not averaged - a higher value will average 2N+1 pixels perpendicular to the trace comb

Edge detection

• Smooth base - 3 is normally a good value
• Smooth counter - 1 default - given i pixels
  • The smoothing increasing with higher values
• Differentiation
  • 0 - give threshold
  • 1 - 1. order differentiation - the derivative - default normally used
  • 2 - 2. order differentiation
• Threshold - the threshold or sensitivity of the edge detector - a lower value increases the sensitivity
  • Percent threshold activates adaptive - threshold is set to N % of maximum values of edges
  • Minimum treshold define minimum value of threshold to accept when adaptive treshold is active
  • Max threshold (peak only) - when active, peaks above this value are ignored. The high peaks are also ignored when the percent threshold is calculated.
• Polarity - All transitions | Light to dark | Dark to light
• Mode - Peak | Threshold
• Edge choice - First | Largest | Last | Nearest | First Nearest | Largest Nearest
  • Largest is default and normally the best choice

Note: Combining adaptive threshold and first edge will help you select the first strong edge

Individual polygons

• Min per polygon match % - when set, every polygon must have at least this match. Normally this default is left off, and each polygon gets an individual value (see the Polygons tab).

Advanced

Polygon match

• Parameters to adjust

  • Translation, rotation - default

  • Translation, scale

  • Translation, rotation, scale, skew

    • Note: good image quality and an increased Repeat Count is needed to get a good fit

    • Note: the shape of the polygon must contain information to be able to calculate all degrees of freedom

  • Translation, rotation, perspective

    • Note: good image quality and an increased Repeat Count is needed to get a good fit

    • Note: the shape of the polygon must contain information to be able to calculate all degrees of freedom

  • Translation, rotation, scale

    • Note: this is done by iterating translation/rotation and translation/scale. The first iteration is always run with translation/rotation; if final fit is selected, it is always run using translation/scale.

• Max repeat count - the number of iteration to fitting the polygons

  • 2 is default but higher values will normally increase the accuracy

  • Lower values will save image processing time

• Stop if result detteriorates - if the match results get worse, the search is stopped. The quality measure of the match can be the match percent, the RMS value or a combination of the two.

  • Hysteresis (%) - allow a small dip in quality before stopping the match

  • RMS factor - weight factor of RMS vs. match count if the combination is selected

• Abort if fit % is less than - stops matching process if less than % edge points is located - used to save time

• Keep best points - the percentage of edge points used in iteration

  • 95 percentage is default

  • A lower value will normally be more robust

• Perform final fit with distance constraints - default on - added to be able to investigate polygon matching in detail

  • Final fit max distance - can be given in pixels or reference coordinates

Child reference base

This sets the origin for the outgoing reference from the tool. The reference is adjusted by the polygon fit results.

• Active - activate child reference base
• Polygon center - use the centerof gravity of the selected model polygon
• Explicit center - set values
  • Origin.X - X value
  • Origin.Y - Y value
• Rotation - the base reference angle

Note : Child reference base is used to fix the model to the object when needed

Advanced2

Result acceptance ( constraints )

• Min match percentage - any of these constraints may make a match invalid
• Max RMS value
• Max angle (abs)
• Max distance
• Max offsetX (abs)
• Max offsetY (abs)
• Hide polygon match items if not accepted - only show polygons if a match is found

The result acceptance is reflected in the OK result - can be used to easily validate the found polygon.

Trace line samples dialog - a helper window to set trace line filter parameters and thresholds

• Middle - show the middle traceline
• Middle+edges - shows the first, middle and last traceline
• Selection - show the selected tracelines
• Line indices - traceline selection
  • example: 2,3,12-15
  • example: 1 3 5 7
• Show trace line popup - activates a modeless traceline window

        
Example tracelines - Middle+edges is selected

Include in description

Include in the onscreen description of valid/invalid match

• Percent
• Offset
• Angle
• Scale

String results

Create Python tuples describing the fitted model:

• Fitted points - the edge points
• Fitted model - the changed model
• Simplify - attempt to simplify the string.
  • Tol (pix) - allow up to this deviation in the simplified polygon

Matching a rectangle

A rectangle can be matched using PM.

This rectangle is matched using Rotation and Translation. The angle is estimated correctly but the center of gravity is moved due to the fact that the model is too long.

The same rectangle is matched using Translation, Rotation and Scale. Both size, rotation and position is correctly and estimated due to the fact that the model is fitted to the object.

The same rectangle is matched using Translation and Scale. The model is not accepted - the red rectangle is the original not accepted model. The green rectangle is the fitted rectangle with size, rotation and position errors.

Polygons

Line definition file - The paths to be searched are initially read from a text file (see the StrVec format). The name of that file is also stored, for possible future reload. The path information, however, is stored directly in the system, without need for the external file.
You can browse for or manually edit the filename; by clicking "Load", the file is read and its contents stored internally. 

• Always read file at startup (overwrite SPB) - With this selection, the file is always loaded at startup.

Polygon properties

• Closed polygons - Select this box if the polygons are closed by default. Individual polygons can be customised separately.

Polygon Editor

• Numbered list - ordered list of polygons. Each polygon can be made active/inactive by clicking the checkbox in front of the number
• Contents - the points of the selected polygon
• New - add polygon
• Delete - remove selected polygon
• Up - moves polygon up in list
• Down - moved polygon down in list
• Paste new - creates a new polygon, pastes the polygon from the clipboard and presses apply  - this is the quickest way to create many polygons
• Highlight selection - highlights the selected polygon in the image
  • used to identify a polygon in the image
• Copy - copies the selected polygon to the clipboard
• Paste - pastes the clipboard to the selected polygon - will overwrite an existing polygon
  • Copy can be used to transfer polygon to the image for editing and modification. The edited polygon is pasted back to the tool using Paste. More on Point and Click Operations
• Snap to model - this will replace all active polygons with the fitted versions. Useful for fine-tuning the polygons to a good picture (model). - Note:  To improve accuracy Snap to model may be executed a number of times - Snap and Apply and Snap again.

Vector mouse menu - activate by right mouse clicking in the Vector list

• New - creates a new vector
• Delete - deletes the selected vector
• Custom trace... - open dialog to define traceline settings for a single polygon
• Custom match... - open dialog to define polygon match settings for a single polygon
• Default trace - remove custom traceline settings for a polygon
• Default match - remove custom polygon match settings for a polygon
• Paste new - paste clipboard as new polygon
• Up - moves polygon up in list
• Down - moved polygon down in list
• Grid... - activate dialog for defining polygon grid
• Delete all - removes all polygons from list
• Delete empty vectors - remove all empty polygons

Autofit - Polygon Model Wizard

Using the Polygon Model Wizard Scorpion helps you create optimal edge polygons for Polygonmatch.

• Autofit polygons
  • When active Ctrl LMouse will make a edge contour along a path or an object

The traceline settings are defined under the Setup tab except:

• Step length
• Start and End of trace lines

Visualize will display the trace line - see image to the right

Note: If Edge trace is difficult - verify wizard settings - long trace lines may cause problems around edge or in corners.

Polygon properties dialog - vector list custom trace choice:

Each polygon can have its own settings, overriding the default values. The custom settings include open/closed, tracelines and edge detection.

Hint: Use individual polygon traceline setting to improve the model

        

Polygon

• Closed polygon - polygon is closed

Trace lines

• Use Traceline Count - selects to specify the traceline count
  • Count - number of trace lines
  • Step length - distance between traceline
    • Ref coord
    • Pixels
• Start point - position of starting point on trace line given in reference coordinates
• End point - position of end point on trace line given in reference coordinates
  • Inverted the sign of start and stop point will change the direction of the trace comb
• Trace step (pixels) - normally 1 - given in pixels
• Line width (pixels) - 0 - trace line is not averaged - a higher value will average N pixels perpendicular to the trace comb

Edge detection

• Smooth base - 3 is normally a good value
• Smooth counter - 1 default - given i pixels
  • The smoothing increasing with higher values
• Differentiation
  • 0 - give threshold
  • 1 - 1. order differentiation - the derivative - default normally used
  • 2 - 2. order differentiation
• Threshold - the threshold or sensitivity of the edge detector - a lower value increases the sensitivity
  • Percent threshold activates adaptive - threshold is set to N % of maximum values of edges
  • Minimum treshold define minimum value of threshold to accept when adaptive treshold is active
  • Max threshold (peak only) - when active, peaks above this value are ignored. The high peaks are also ignored when the percent threshold is calculated.
• Polarity - All transitions | Light to dark | Dark to light
• Mode - Peak | Threshold
• Edge choice - First | Largest | Last | Nearest - Largest is default and normally the best choice
• Set default - reset all custom values

Polygon properties dialog - vector list custom polygon match choice:

Each polygon can have its own settings, overriding the default values. This can be very useful to e.g. verify very small details in an image.

• Min match percent - match will succeed only if this particular polygon has this match percent. This can be a small detail that must be present in the image
• Exclude from total match - use this polygon in the fit process, but ignore its results
• Set default - reset all custom values

Add polygon

Rectangle and Circle can be added as polygon using this tab. This is valuable when working with these shapes.

Point & Click Support

Two points will define a circle - first point is circle center and the seconds defines the radius. Four points will define a rectangle. Ctrl-Z will paste the clipboard to the tool. Ctrl-A will add the object to the polygon vector list

Visualisation

Center	Center of found polygon
CenterAxes	Orientation of match
Description	Description of accepted polygon (see Advanced2 page)
Description (invalid)	Description of non-accepted polygon (see Advanced2 page)
EdgePoints	Edge points, final iteration
EdgePointsOrig	Edge points, first iteration
FittedPoints	Fitted points final iteration
FittedPointsOrig	Fitted points first iteration
MatchedPolygon	The best fitted polygon
MissingPoints	Tracelines without edgepoints, final iteration
MissingPointsOrig	Tracelines without edgepoints, first iteration
NonAcceptedPolygon	The original model is visualised when no match
OriginalPolygon	The original model
OutlierPoints	Points too far from polygon, final iteration
OutlierPointsOrig	Points too far from polygon, first iteration
TraceLines	Tracelines, final iteration
TraceLinesOrig	Tracelines, first iteration

Results 

Iterations	Number of performed iterations (less than specified if no match)
Fit percent	Percent of tracelines that has a point that is accepted
RMS	RMS value of the fitted polygons
OK	1 if fit OK, 0 otherwise
Offset X	Movement of fitted polygon, x
Offset Y	Movement of fitted polygon, y
Distance	Total movement of fitted polygon
Angle	Rotation of fitted polygon
Scale X	Scaling of fitted polygon, x
Scale Y	Scaling of fitted polygon, y
Skew	Axis skew
Origin.x	Position of base, x
Origin.y	Position of base, y
Fitted points	The final fitted edge points
Fitted model	The original model, moved to best position

ExecuteCmd support (see also executeCmd)

Command	Parameters	Return values	Comments
Set	Object=ROI;Value=<polygon>	ok,None	Sets the first ROI polygon. See Copy/paste ROIs for details. (*)
Set	Object=ROI;Number=<number>; Value=<polygon>	ok,None	Sets the numbered ROI polygon. See Copy/paste ROIs for details. (*)
Add	Object=ROI;Value=<polygon>	ok,None	Adds ROI polygon to the end of the list. See Copy/paste ROIs for details.
Get	Object=ROI;Number=<number>	ok,<polygon>	Gets numbered polygon, as Scorpion polygon (StrArr format).
Get	Object=Tuple;Number=<number>	ok,<tuple>	Gets numbered polygon, as Python tuple
Clear	Object=ROI;Number=<number>	ok,None	Clears numbered polygon (makes empty)
DeleteAll	-	ok,None	Deletes all polygons
SnapToModel	-	ok,None	Replaces active polygons with the best fit in the image. OK to run also when the tool dialog is open.

(*) Note: Polygon properties are not supported by these methods, although existing properties will be kept when the SET command is used.

Example 1: Copy a polygon from the clipboard

tool =  GetTool('PM')
tool.executeCmd('Set','Object=ROI;Number=1;source=clipboard')

Example 2: Copy a polygon to the clipboard

tool =  GetTool('PM')
tool.executeCmd('Get','Object=ROI;Number=1;destination=clipboard')

Example 3: Add model from Clipboard and Snap the model

pm=GetTool('StickerPosition')
pm.executeCmd('Set','Object=ROI;Number=1;source=clipboard')
ExecuteCmd('InspectExecute','')  # inspection needed for SnapToModel 
pm.executeCmd ('SnapToModel','')
ExecuteCmd('InspectExecute','')

Keyboard shortcuts - More information

Shortcut	Command	Comments
Ctrl-Z	Set ROI	Sets the selected polygon to points marked in the image. If only a single point is marked, the polygon is moved, centered around the point. If the tool dialog is not open, the first polygon is set.
Ctrl-P	Snap to model	Replaces active polygons with the best fit in the image. OK to run also when the tool dialog is open.
Ctrl-1 - Ctrl-0	Set polygon 0-10	Sets the numbered polygon to points marked in the image. If only a single point is marked, the polygon is moved, centered around the point. If a new polygon is defined this way, any missing polygons in between are set as empty.
Ctrl-Shift-1 - Ctrl-Shift-0	Clear polygon 0-10	Clears the numbered polygon (sets empty).

Example 4: Iterating Edge Mode when no match using Tool Scripting

# init
def init(self):
  tool = GetTool(self.name)
  tool.setConfigValue('EdgeSelect',0) # first

#afterExecute
def afterExecute(self):
  #use self.name to get this tool instance
  #Return 1 for OK, 0 for new execution
  tool = GetTool(self.name)
  ok = tool.getBoolValue('OK')
  edgeMode = tool.getConfigValue('EdgeSelect')
  if not ok and edgeMode < 2:
    tool.setConfigValue('EdgeSelect',3)
    print 'A_polygonfind retry edgeselect 3'
    return 0 # new execution
  else:
    return 1