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== Walkthrough of omclock.py == | == Walkthrough of omclock.py == | ||
Revision as of 18:43, 13 October 2010
The overhead_map webpage allows one to display images, lines, points, and arrows on a top-down rendering of a real-world surface.
Contents |
Installation
The overhead visualization system requires a current version of brown-ros-pkg, which includes packages for rosjs (ROS JavaScript interface), om_msgs (ROS overhead map messages), and [1] (overhead_map JavaScript Applet). Assuming brown-ros-pkg is installed, it can be updated by:
> roscd irobot_create_2_1/../.. # (ie, the root directory of brown-ros-pkg) > svn update
The om_msgs package needs to be "compiled" so that the message types Overhead_Map_Obj and Overhead_Map_Objs are available:
> rosmake om_msgs
You will also need a websockets compatible web browser* (check), such as Chrome 4+, Firefox 4+, or Safari 5+
- *Note: As a security feature, Chrome does not handle ajax requests under file:// unless explicitly allowed; if you are using Chrome, the web browser must either access overhead_map.html via http or must be launched with "--allow-file-access-from-files". (Other browsers, eg Firefox 4 beta, do not have this problem, and can alternatively be used for this case.)
Introduction: Running omclock example on a single machine
To test that we can get everything up and working, we will use omclock, which draws a clock face with the current time on a soccer field. Once this is up and running, one can easily swap omclock with any other node that publishes Overhead_Map_Objs messages to allow for custom visualizations.
omclock has a built-in launch file, which will start omclock and rosjs:
> roslaunch omclock omclock.launch
Next, point your web browser to:
file://[PATH-TO-brown-ros-pkg]/experimental/overhead_map/overhead_map.html
where the "PATH-TO-brown-ros-pkg is the local path to brown-ros-pkg. For example, in Brian's test, he visits the page:
file:///home/brian/ros/stacks/brown-ros-pkg/experimental/overhead_map/overhead_map.html
If successful, you should see a rendering of the CS148 field with a clock.
Running overhead_map with custom code
If all overhead_map could do was run clock applications, it would be pretty useless! The good news, though, is that it is a very straightforward process to move away from the demo provided and completely swap it with your code.
Simply put, to publish messages to overhead_map, one needs to publish messages of type Overhead_Map_Objs (defined in om_msgs/msg) to the topic "overhead_map_objs". (In fact, this is exactly what omclock does.) When a web browser is directed to the overhead_map page, overhead_map communicates to rosjs via WebSockets to ask rosjs to subscribe to said topic; rosjs then listens for the topic in ROS and forwards the messages to overhead_map. overhead_map then renders the messages on-screen as they arrive. In each rendering, only the last sent message is rendered.
Details about the publishing format for om_msgs can be found in om_msgs/msg/Overhead_Map_Obj.msg and om_msgs/msg/Overhead_Map_Objs.msg. Below, we will walk step-by-step through omclock's source code to show how to publish this message type.
Using overhead_map on multiple machines
One of the perks of the overhead_map system is its modularity; the computer serving webpages, the computer publishing overhead_map information, and the computer viewing the information published can be three completely separate entities! This section will explain the exact division of labor and how to connect the divided laborers together over a local network.
The three tasks at hand are:
- Server: A web server (with IP address [server]) which hosts overhead_map. The server hosts the overhead_map folder, which includes (among other things) html, javascript, and images. No special software is needed for this role beyond a traditional web server (such as Apache).
- Robot: A robot (with IP address [robot]) which runs ROS (including the rosjs node) and publishes Overhead_Map_Objs messages on the topic "overhead_map_objs".
- Laptop: A laptop (or other computer) which views the overhead_map webpage. No special software is needed for this role beyond a websockets-compatible browser.
Any single machine may take on one or multiple roles, which interact in the following manner:
- The laptop retrieves html, javascript, and image files from the server, like any typical http exchange.
- The laptop establishes a connection with the robot via WebSockets. This connection is then used to send Overhead_Map_Objs messages from the robot to the laptop. (Because WebSockets are bidirectional, one may also send information from the laptop to the robot, but this feature is not used by overhead_map.)
- The server and robot do not interact.
Installation
- Server: Install a http server, and place the overhead_map folder in a location accessible from other computers via http. (For example, in Apache, this defaults to any files inside of /var/www on Ubuntu machines. (More information)) When we refer to "the overhead_map website" below, we will be referring to:
http://[server]/[overhead_map-path]/overhead_map.html?address=[robot]
Alternatively, if server and laptop are the same computer, we can look up the website without an http server, in which case when we refer to "the overhead_map website" below, we will be referring to:
file://[path-to-brown-ros-pkg]/experimental/overhead_map/overhead_map.html?address=[robot]
If the robot and laptop are the same computer, the "?address=[robot]" querystring may be left off. (This value defaults to 127.0.0.1, ie the local computer.)
- Robot: Follow the single-machine installation instructions. It is not necessary to install a WebSockets-compatible browser here unless the robot and laptop are the same computer.
- Laptop: Follow the single-machine installation instructions for installing a WebSockets-compatible browser.
Multi-machine introduction: Running omclock example on multiple machines machine
This example will closely follow the single-machine example for running omclock, but it is adapted to use three (or two (or even one)) machines. Like in the single-machine example, after omclock is up and running, it is simple to swap out the omclock node for a custom node on your robot.
- Make sure the server is running and available.
- On the robot, run the omclock demo:
> roslaunch omclock omclock.launch
- Point the laptop's web browser to "the overhead_map website" (as described in the installation section above).
If successful, on the laptop you should see a rendering of the CS148 field with a clock.
Customizing overhead_map
The overhead_map package was designed to be very flexible with regard to the images, measurements, etc. used. The icons (such as the "irobot-create" picture), backgrounds (such as the soccer field), and logos (such as the center Brown logo and the RLAB logo in the bottom-right) are all customizable without ever touching the Javascript code.
We will demonstrate how to customize the field by means of example. Robot soccer is fun, but let's supppose you wanted to play robot tennis. We will demonstrate how to completely customize the display to allow this to happen.
Adding backgrounds
A soccer field probably won't do too well, here. Let's make a new background. Navigate to the overhead_map base directory and then to the "backgrounds" subdirectory. Notice that the word "soccer" is present in three of these files:
soccer.svg soccer.png soccer.xml
Of these, only soccer.png and soccer.xml are completely necessary. (soccer.svg was the file used to create the soccer field as a vector graphic, which was then converted into png. We use png files because some browsers (such as the current Firefox 4 Beta) cannot draw svg files inside of html5 canvases, so this increases cross-browser compatibility.)
Start by making a tennis field image with the name tennis.png:
The dimensions are arbitrary, but for appearance, it is good to keep files at a reasonably high resolution and at approximately the right proportions.
Next we will add a new xml file for the tennis background. The xml file specifies the "real-world" coordinates of the tennis field, so that we don't need to think of how the field is rendered graphically; we can instead specify where we want things placed in a natural way. In this case, let's do our measurements in feet, since tennis courts are traditionally measured in those units:
<field>
<width>78</width>
<height>36</height>
<border_color>rgb(241,110,45)</border_color>
<marker_color>rgb(255,255,0)</marker_color>
</field>
The border_color field specifies the color to be drawn around the tennis court. The border is drawn so that any objects that are partially off the field will still be drawn fully on the screen. The marker_color field specifies the color of markers (such as points, lines, and arrows) drawn on the field. Here, we've chosen the border to be reddish and the markers to be yellow.
Now that we've added the tennis background, we would like to see it! We can do this much like the examples above by running rosjs and roscore, and by then pointing our web browser to:
file://[path-to-brown-ros-pkg]/experimental/overhead_map/overhead_map.html?map=tennis
(By adding "map=tennis" to the querystring, we tell overhead_map to draw using the tennis map instead. By default, we use the soccer map.) If all goes well, you should see the tennis court!
Adding/changing logos
Let's change the logos; we might not be affiliated with [Brown University] or [rlab]. But let's say we are associated with [ROS.org]. We will put the ROS.org logo in the bottom right, and we'll get rid of the center image.
First, to get rid of the center image, we'll replace it with a blank image. Conveniently, there's one already available. Navigate to the overhead_map base directory and then to the "logos" subdirectory.
> ls blank.png bottom-right.png center.png > cp blank.png center.png
Now, the center logo has been replaced by a transparent pixel.
Next we will change the bottom-right image to the ROS logo from the top of the main website. To make it fit in better, we'll change the white color to be transparent and shrink it 75% (so that it fits in our picture nicely). (Call this image "new-ros-picture.png".) Then, in the overhead_maps/logos directory:
> ls blank.png bottom-right.png center.png new-ros-picture.png > mv new-ros-picture.png bottom-right.png
...and we're done! (Depending on how your web browser caches images, you may need to reload the page or restart the browser.)
Adding/changing icons
Finally, if we're playing tennis, we'll certainly need a tennis ball icon! ...
Walkthrough of omclock.py
omclock handles each of the 4 basic types of messages passable by om_msgs, so it will be used to demonstrate how each of these is used. omclock.py can be found by:
> roscd omclock/bin > gedit omclock.py # or your favorite editor
Breakdown of omclock.launch
In the om_clock example, the launch file starts ROS nodes for rosjs and omclock (to drive the clock behavior):
<launch> <node name="rosjs" pkg="rosjs" type="rosjs.py" /> <node name="omclock" pkg="omclock" type="omclock.py" /> </launch>
Breakdown of overhead_map.js and usage in html
The example webpage for the om_clock example contains a overhead_map JavaScript object, such as the one contained in brown-ros-pkg. overhead_map.js uses rosjs to listen for messages related to the visualizing overhead localization topics and a canvas element to render these objects in the web browser. Note: This page depends on jQuery, the jQuery query string object plugin, and ros.min.js which are available either locally (as provided in overhead_map/js) or accessible online.
<html>
<head>
<title>Overhead Map</title>
<script type="text/javascript" src="js/jquery-1.4.2.min.js"></script>
<script type="text/javascript" src="js/jquery.query.js"></script>
<script type="text/javascript" src="js/ros.min.js"></script>
<script type="text/javascript" src="overhead_map.js"></script>
</head>
<body>
<table>
<tr><td>
<!-- canvas width/height controls the max. size of the board -->
<canvas id="board" width="800" height="600" ></canvas>
</td></tr>
<tr><td>
Log:
</td></tr>
<tr><td>
<textarea id="console" rows="10" cols="80" readonly="readonly"></textarea>
</td></tr>
</table>
</body>
</html>
Message types
First, let's look at how our messages are specified. For each desired update, we will pass a single message of type Overhead_Map_Objs -- essentially, a list with elements of type Overhead_Map_Obj -- to rosjs. rosjs will then use websockets to send this information to your web browser, resulting in the clock appearing on your screen. The message types the overhead_map system (including but not limited to overhead_map, omclock, and omdc) uses are in the ROS node om_msgs:
> roscd om_msgs/msg
There are two message types specified, namely Overhead_Map_Obj.msg and Overhead_Map_Objs.msg
Overhead_Map_Obj.msg:
# For each type of name, there is an associated tuple: # * "point": [x y] draws a point at (x, y) # * "line": [x0 y0 x1 y1] draws a line from (x0, y0) to (x1, y1) # * "arrow": [x0 y0 x1 y1] draws an arrow (x0, y0) --> (x1, y1) # * "imname": [x y th] draws an image named "imname" centered # at (x,y), rotated th radians. # location of image is # "$OVERHEAD_MAP_ROOT/icons/imname.png". string name float32[] tuple
Overhead_Map_Objs.msg:
Header header Overhead_Map_Obj[] objs
Scaffolding
Let's start making omclock.py. There's a bit of ROS scaffolding to do first:
#!/usr/bin/env python
import roslib; roslib.load_manifest('omclock')
import rospy, time
from math import cos,sin,pi
from om_msgs.msg import Overhead_Map_Obj, Overhead_Map_Objs
def go():
pub = rospy.Publisher('overhead_map_objs',Overhead_Map_Objs)
rospy.init_node('omclock')
# main control loop
r = rospy.Rate(10) # hz
while not rospy.is_shutdown():
#
#
# Make the clock!
#
#
# wait for next loop
r.sleep()
# Input: propTime in [0,1]
# propTime is, eg, hours/12 or minutes/60
# Returns the angle (in radians) of the clock pointer at
def clockAngle(propTime):
return (2*pi*(1-propTime)) + pi/2
def dtrace(s,x): # for debugging
rospy.loginfo(s+" == %s"%x)
return x;
if __name__ == '__main__':
go()
Basically, we are setting Python up to publish messages of type Overhead_Map_Objs on topic "overhead_map_objs" and to publish the information at about 10 frames per second. (This will let the robot, which represents the second hand, look like it is driving around the clock face.) We also have some helper functions tangential to this walkthrough, which won't be investigated further.
Making the clock
We will now create the clock face by using "Overhead_Map_Obj"s by filling the "Make the clock!" comment.
Before we can do that, however, we need to know how the coordinate system is set up. All the drawing in overhead_map is performed relative to an "ideal" coordinate frame, which is similar to the one presented in math classes. In our frame, the bottom-left corner of the background is at point (0,0), x points rightward, and y points upward. Theta is measured in radians, is equal to zero when pointing towards +x, and increases as one rotates counterclockwise. The unit is declared arbitrarily, and is meant to be some sort of real-world measure. For example, the "soccer field" in real life is about 4 meters long and 2.5 meters high, so the soccer map is configured to represent the area surrounded by coordinates (0,0), (4,0), (4,2.5), and (0,2.5), and one draws objects by specifying them in ideal coordinates. For instance, if one sees an iRobot Create centered at the real world at coordinates (3,1), one can simply instruct overhead_map to draw a picture of the iRobot Create at (3,1); all the graphics processing and rendering is handled behind-the-scenes by overhead_map.js!
Let's start making the clock by setting up some constants and reading in the time:
# Get time. Make an analog clock face with center (centerX,centerY)
# and largest radius "radius"
# This one's set up for the soccer field's center
centerX = 2
centerY = 1.25
radius = 1
curTime = time.localtime();
hours = curTime.tm_hour
minutes = curTime.tm_min
seconds = curTime.tm_sec + (time.time()%1) # for partial seconds
Arrow
Now, let's draw the hour hand using an arrow:
# Hour hand is an arrow
hourAngle = clockAngle((hours+minutes*1./60+seconds*1./3600)*1./12)
hourHand = Overhead_Map_Obj()
hourHand.name = "arrow"
hourHand.tuple = [centerX,
centerY,
centerX+0.5*radius*cos(hourAngle),
centerY+0.5*radius*sin(hourAngle)]
There is a bit of computation happening to compute the angle the hour hand needs to face, but let's not worry about the details. The important bits are:
hourHand = Overhead_Map_Obj()
which makes the object,
hourHand.name = "arrow"
which tells overhead_map to draw the object as an arrow, and
hourHand.tuple = [A,B,C,D]
which tells overhead_map to draw an arrow from (A,B) to (pointing toward) (C,D) as specified in Overhead_Map_Obj.msg:
# * "arrow": [x0 y0 x1 y1] draws an arrow (x0, y0) --> (x1, y1)
The name and tuple together form a complete specification of an Overhead_Map_Obj.
Line
Next, we'll draw the minute hand using a line:
# Minute hand is a line
minuteAngle = clockAngle((minutes+seconds*1./60)*1./60)
minuteHand = Overhead_Map_Obj()
minuteHand.name = "line"
minuteHand.tuple = [centerX,
centerY,
centerX+0.75*radius*cos(minuteAngle),
centerY+0.75*radius*sin(minuteAngle)]
Note the only difference between it and the hour hand is that the name is "line" instead of "arrow"; otherwise, the code takes the same form, as specified in Overhead_Map_Obj.msg:
# * "line": [x0 y0 x1 y1] draws a line from (x0, y0) to (x1, y1)
Image
Next, we'll draw the second hand by using an image of the iRobot Create:
# Second "hand" is a robot going around the outside
secondAngle = clockAngle(seconds*1./60)
secondHand = Overhead_Map_Obj()
secondHand.name = "irobot-create"
secondHand.tuple = [centerX+radius*cos(secondAngle),
centerY+radius*sin(secondAngle),
secondAngle-pi/2]
Creating the blank Overhead_Map_Obj is the same as usual. The name of this object is "irobot-create", which is an image stored in overhead_map's icon subdirectory; recall from Overhead_Map_Obj.msg:
# * "imname": [x y th] draws an image named "imname" centered # at (x,y), rotated th radians. # location of image is # "$OVERHEAD_MAP_ROOT/icons/imname.png".
The tuple we created reflects the x, y, and theta coordinates desired.
Point
Finally, let's put a dot in the center of the clock for looks, using a point:
# Center "dot"
centerDot = Overhead_Map_Obj()
centerDot.name = "point"
centerDot.tuple = [centerX, centerY]
Note the name "point" and the tuple specified in Overhead_Map_Obj.msg:
# * "point": [x y] draws a point at (x, y)
Merging "Overhead_Map_Obj"s into one "Overhead_Map_Objs", and publishing
To merge all the objects we want drawn, we simply create an instance of Overhead_Map_Objs and put all of our objects in that instance's ".objs" field:
# Put it all together (front drawn first)
drawing = Overhead_Map_Objs()
drawing.objs = [secondHand, minuteHand, hourHand, centerDot]
Finally, we need to publish our instance of Overhead_Map_Objs to rosjs:
pub.publish(drawing)
...and our clock is drawn!
Full Source Code
Here's the entirety of omclock.py:
#!/usr/bin/env python
import roslib; roslib.load_manifest('omclock')
import rospy, time
from math import cos,sin,pi
from om_msgs.msg import Overhead_Map_Obj, Overhead_Map_Objs
def go():
pub = rospy.Publisher('overhead_map_objs',Overhead_Map_Objs)
rospy.init_node('omclock')
# main control loop
r = rospy.Rate(10) # hz
while not rospy.is_shutdown():
# Get time. Make an analog clock face with center (centerX,centerY)
# and largest radius "radius"
# This one's set up for the soccer field's center
centerX = 2
centerY = 1.25
radius = 1
curTime = time.localtime();
hours = curTime.tm_hour
minutes = curTime.tm_min
seconds = curTime.tm_sec + (time.time()%1) # for partial seconds
# Hour hand is an arrow
hourAngle = clockAngle((hours+minutes*1./60+seconds*1./3600)*1./12)
hourHand = Overhead_Map_Obj()
hourHand.name = "arrow"
hourHand.tuple = [centerX,
centerY,
centerX+0.5*radius*cos(hourAngle),
centerY+0.5*radius*sin(hourAngle)]
# Minute hand is a line
minuteAngle = clockAngle((minutes+seconds*1./60)*1./60)
minuteHand = Overhead_Map_Obj()
minuteHand.name = "line"
minuteHand.tuple = [centerX,
centerY,
centerX+0.75*radius*cos(minuteAngle),
centerY+0.75*radius*sin(minuteAngle)]
# Second "hand" is a robot going around the outside
secondAngle = clockAngle(seconds*1./60)
secondHand = Overhead_Map_Obj()
secondHand.name = "irobot-create"
secondHand.tuple = [centerX+radius*cos(secondAngle),
centerY+radius*sin(secondAngle),
secondAngle-pi/2]
# Center "dot"
centerDot = Overhead_Map_Obj()
centerDot.name = "point"
centerDot.tuple = [centerX, centerY]
# Put it all together (front drawn first)
drawing = Overhead_Map_Objs()
drawing.objs = [secondHand, minuteHand, hourHand, centerDot]
pub.publish(drawing)
# wait for next loop
r.sleep()
# Input: propTime in [0,1]
# propTime is, eg, hours/12 or minutes/60
# Returns the angle (in radians) of the clock pointer at
def clockAngle(propTime):
return (2*pi*(1-propTime)) + pi/2
def dtrace(s,x):
rospy.loginfo(s+" == %s"%x)
return x;
if __name__ == '__main__':
go()
Example Code
Some code was written to test the functionality of overhead_map and may provide a good starting ground for hacking or additional insight.
- omclock: A simple "clock" application to test that all is running well on your system by drawing an analog clock on the overhead_map soccer field. The included launch file (omclock.launch) will launch omclock and rosjs, and it will attempt to launch Google Chrome to display output. (This last step can also be accomplished manually by directing your browser.)
> roslaunch omclock omclock.launch
- omdc: A display controller which takes planar_tracker messages as input and publishes overhead_map messages as output. This can be used, for instance, to create a top-down visualization of a field with objects identifiable by color blobs or AR Tags.