Robot modelling formats for simulation

Several XML-based formats have surfaced over the years that can be used to describe a robot.

Apart from URDF (and SRDF) of ROS origin, the Gazebo simulator has been promoting SDF (an evolution of URDF with emphasis on physics simulation), while MJCF apart from being available as URDF extensions, also has its own format with an XML schema for validation and more advanced simulation features (e.g. tendons).

URDF (ROS)

http://wiki.ros.org/urdf

http://wiki.ros.org/urdf/XML

http://wiki.ros.org/urdf/XML/joint

http://wiki.ros.org/urdf/XML/link

Also related, units of measurement in ROS: http://www.ros.org/reps/rep-0103.html

SRDF format http://wiki.ros.org/srdf that is mentioned at http://wiki.ros.org/robot_model is also related (adds Semantics like kinematic chain definition etc). As explained there it is combined with URDF in describing a robot:

This does not replace URDF, and is not an extension of URDF.

This is a format for representing semantic information about the robot structure.

A URDF file must exist for this robot as well, where the joints and the links that are referenced are defined

SDF (Gazebo)

http://gazebosim.org/tutorials?tut=build_model

http://sdformat.org
http://sdformat.org/spec

https://bitbucket.org/osrf/gazebo_models/src (various SDF models in XML)

http://gazebosim.org/tutorials/?tut=ros_urdf (Converting from URDF to Gazebo)

http://gazebosim.org/tutorials?tut=simple_gripper (tutorial for simple gripper in SDF)

Gazebo seems to be using ODE (Open Dynamics Engine), so these are related too:

http://www.ode.org/ode-latest-userguide.html#sec_7_3_0 (see images for Joint types)

http://www.ode.org/ode-latest-userguide.html#sec_3_6_0 (ERP & CFM constraint parameters)

MJCF (MuJoCo)

http://www.mujoco.org/ (MuJoCo 1.50 was released on April 23, 2017. Student licenses are now free)

http://www.mujoco.org/book/

http://www.mujoco.org/book/modeling.html

http://www.mujoco.org/book/modeling.html#CURDF (MJCF is an advanced format but some of its functionality is also available as URDF extensions)

http://www.mujoco.org/book/computation.html#Constraint (MuJoCo has constraints like Connect/Weld/Joint/Tendon/Distance)

https://homes.cs.washington.edu/~todorov/papers/TodorovIROS12.pdf (see paragraph «B. Elements of a MuJoCo model»)

URDF to MJCF conversion is possible (related sample available for MuJoCo):

http://www.mujoco.org/forum/index.php?threads/urdf-mjcf-conversion.3429/

There is ongoing work at Bullet Physics engine to import MJCF, as mentioned at:

https://github.com/bulletphysics/bullet3/releases

Thus, they have collected various MJCF models (XML):

https://github.com/bulletphysics/bullet3/tree/master/data/mjcf

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Background info on libpng warning: iCCP: known incorrect sRGB profile

I was just checking some log file saved from Buildbox and seems Qt framework was logging the error:

libpng warning: iCCP: known incorrect sRGB profile

Did some quick research on Google (sorry dear Bing) and added the following background info to the respective question on StackOverflow:

http://stackoverflow.com/questions/22745076/libpng-warning-iccp-known-incorrect-srgb-profile/

Some changes in libpng version 1.6+ cause it to issue a warning or even not work correctly with the original HP/MS sRGB profile, leading to the following stderr: libpng warning: iCCP: known incorrect sRGB profile The old profile uses a D50 whitepoint, where D65 is standard. This profile is not uncommon, being used by Adobe Photoshop, although it was not embedded into images by default.

(source: https://wiki.archlinux.org/index.php/Libpng_errors)

Error detection in some chunks has improved; in particular the iCCP chunk reader now does pretty complete validation of the basic format. Some bad profiles that were previously accepted are now rejected, in particular the very old broken Microsoft/HP sRGB profile. The PNG spec requirement that only grayscale profiles may appear in images with color type 0 or 4 and that even if the image only contains gray pixels, only RGB profiles may appear in images with color type 2, 3, or 6, is now enforced. The sRGB chunk is allowed to appear in images with any color type.

(source: https://forum.qt.io/topic/58638/solved-libpng-warning-iccp-known-incorrect-srgb-profile-drive-me-nuts/16)

Fix: Delphi error MSBuildToolsPath is not specified for the ToolsVersion …

This is my answer at:

http://stackoverflow.com/questions/32936544/delphi-10-seattle-trial-fails-to-compile-anything-gives-an-msbuild-error

for the issue of Delphi showing on build the error

MSBuildToolsPath is not specified for the ToolsVersion “12.0” defined at “HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\MSBuild\ToolsVersions\12.0”, or the value specified evaluated to the empty string

note that in my case it was also showing underlined unit names in the code editor at uses clause with “Cannot resolve unit name xx”

---

It is a known issue, documented here: https://community.embarcadero.com/article/technical-articles/16202-msbuildtoolspath-is-not-specified-for-the-toolsversion

This error is caused by incorrect values in the registry. On a 32 OS, run regedit and navigate to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\MSBuild. On a 64 bit OS, run regedit and navigate to HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\MSBuild. First, backup this registry key by selecting File | Export. Next, look at the numbers below the ToolsVersions key. Delete any number not found at the MSBuild level. … There is anecdotal evidence to suggest this registry key imbalance is caused by uninstalling some versions of Visual Studio, but it has not been confirmed at this time.

Since I’ve been installing/uninstalling various Visual Studio versions (including previews), guess it has indeed been caused by that

Error “A default tools version “2.0” was specified, but its definition could not be found.” may appear then if you deleted the 2.0 key following the 1st article’s advice. Solution for that one is to edit each value under MSBuild key in the registry locations mentioned for x32 and x64 and change DefaultToolsVersion to 14.0 or other highest MSBuild tools version that is installed

Note that on x64 machine you need to fix these two issues for both x32 and x64 registry locations, since the IDE is 32-bit process and if you fix x64 location only it will fail internally, underlining all Standard units at uses clause in your source code at uses clause and showing “Cannot resolve unit name xx”

Also it may be useful to install this: https://www.microsoft.com/en-us/download/confirmation.aspx?id=48159

This may also be useful to know (copying from https://msdn.microsoft.com/en-us/library/bb383985.aspx):

Order of Precedence

The order of precedence, from highest to lowest, used to determine the ToolsVersion is: The ToolsVersion attribute on the MSBuild task used to build the project, if any.

The /toolsversion (or /tv) switch that’s used in the msbuild.exe command, if any.

If the environment variable MSBUILDTREATALLTOOLSVERSIONSASCURRENT is set, then use the current ToolsVersion.

If the environment variable MSBUILDTREATHIGHERTOOLSVERSIONASCURRENT is set and the ToolsVersion defined in the project file is greater than the current ToolsVersion, use the current ToolsVersion.

If the environment variable MSBUILDLEGACYDEFAULTTOOLSVERSION is set, or if ToolsVersion is not set, then the following steps are used:

The ToolsVersion attribute of the Project element of the project file. If this attribute doesn’t exist, it is assumed to be the current version.

The default tools version in the MSBuild.exe.config file.

The default tools version in the registry. For more information, see Standard and Custom Toolset Configurations.

If the environment variable MSBUILDLEGACYDEFAULTTOOLSVERSION is not set, then the following steps are used:

If the environment variable MSBUILDDEFAULTTOOLSVERSION is set to a ToolsVersion that exists, use it.

If DefaultOverrideToolsVersion is set in MSBuild.exe.config, use it.

If DefaultOverrideToolsVersion is set in the registry, use it.

Otherwise, use the current ToolsVersion.

Nested LINQ Aggregate queries vs Nested Foreach statements example

At Trafilm project’s Metadata (http://github.com/zoomicon/Trafilm.Metadata) I have a linked data structure where a Film contains multiple Conversations which contain multiple L3STinstances, which in turn contain multiple L3TTinstances.

I had the need to calculate a list of all unique L2language values of L3TTinstance grand-grand-children for a Film (to keep as calculated metadata for display at the Films PivotViewer collection available at http://gallery.trafilm.net/collection/films.cxml (that is a Collection XML file), which you can explore via HTML5 PivotViewer (seajax) at http://gallery.trafilm.net/film).

BTW, other objects mentioned have their own separate PivotViewer galleries (shown at http://gallery.trafilm.net/conversation, http://gallery.trafilm.net/L3STinstance, http://gallery.trafilm.net/L3TTinstance respectively). Note that the metadata for the respective collections is still being populated at the time of writing, but some sample data is included to try out.

 

Initially I did it with nested LINQ Aggregate expressions:

L2dubbedLanguages = value.Aggregate(new List<string>(), (total, conversation) =>

  (conversation == null) ? total :

              conversation.L3STinstances.Aggregate(total, (totalST, l3STinstance) =>

     (l3STinstance == null) ? totalST :

           l3STinstance.L3TTinstances.Aggregate(total, (totalTT, l3TTinstance) =>

       {

          if ( (l3TTinstance != null) &&

               !string.IsNullOrEmpty(l3TTinstance.L2language) &&

               (l3TTinstance.L2mode == "Dubbed") &&

               !totalTT.Contains(l3TTinstance.L2language) )

            totalTT.Add(l3TTinstance.L2language);

          return totalTT; //note that totalTT == totalST == total

       }

  ))).ToArray();

 

However, since I also had to repeat again all the code block shown above for the “Subtitled” L2languages (just replacing the “Dubbed” string comparison in it), it was more optimal to combine the two in one code block using nested foreach statements that host one switch statement:

//Calculated from Conversations.L3STinstances.L3TTinstances//

IList<string> dubbed = new List<string>();
IList<string> subtitled = new List<string>();
foreach (Conversation conversation in value)
  if ((conversation != null) && (conversation.L3STinstances != null))
    foreach (L3STinstance l3STinstance in conversation.L3STinstances)
      if ((l3STinstance != null) && (l3STinstance.L3TTinstances != null))
        foreach (L3TTinstance l3TTinstance in l3STinstance.L3TTinstances)
          if (l3TTinstance != null)
          {
            string l2language = l3TTinstance.L2language;
            if (!string.IsNullOrEmpty(l2language))
              switch (l3TTinstance.L2mode)
              {
                case "Dubbed":
                  if (!dubbed.Contains(l2language))
                    dubbed.Add(l2language);
                  break;
                case "Subtitled":
                  if (!subtitled.Contains(l2language))
                    subtitled.Add(language);
                  break;
              }
          }
L2dubbedLanguages = dubbed.ToArray();
L2subtitledLanguages = subtitled.ToArray();

 

Having done this refactoring, I decided to also change some of the Conversation object’s calculated fields with a LINQ Aggregate:

L3STlanguages = value.Aggregate(new List<string>(),
  (total, l3STinstance) => { 
     if ((next != null) && 
         !string.IsNullOrEmpty(l3STinstance.L3STlanguage) && 
         !total.Contains(l3STinstance.L3STlanguage)) 
       total.Add(l3STinstance.L3STlanguage);
     return total;
}).ToArray();

and which had to be repeated again for the L3STlanguageType field (that is by just changing L3STlanguage to L3STlanguageType in the code block above), to the following nested foreach statements’ code block:

IList<string> languages = new List<string>();
IList<string> languageTypes = new List<string>();
foreach(L3STinstance l3STinstance in L3STinstances)
  if (l3STinstance != null)
  {
    string language = l3STinstance.L3STlanguage;
    if (!string.IsNullOrEmpty(language) &&
        !languages.Contains(language))
      languages.Add(language);

    string languageType = l3STinstance.L3STlanguageType;
    if (!string.IsNullOrEmpty(languageType) &&
        !languageTypes.Contains(languageType))
      languageTypes.Add(languageType);
  }
L3STlanguages = languages.ToArray();
L3STlanguageTypes = languageTypes.ToArray();

That should also avoid any intermediate memory objects overhead that comes with usage of LINQ for Aggregation.

HowTo: Hide HTML markup from non-signedin users at MonoX Social CMS

At MonoX Social CMS, which I use at both ClipFlair Social and Trafilm websites, I was in the need of hiding some HTML markup when the user is not signed-in.

The solution for this is to add runat="server" to the HMTL element one wants to hide and then set the Visible property that the object acquires due to the runat clause. The Visible property is set using some special syntax to access the MonoX API like below:

<ul runat="server"
      Visible="<% $Code: Page.User.Identity.IsAuthenticated %>"  >

…

</ul>

Redirecting output of batch file from the inside

Calling a label in a batch file is useful to redirect (for logging) the output of the batch file to a file from inside that same batch file, without needing to author a separate batch file to do the redirect of standard output.

@echo off

call :process > update_cxml.log
goto :EOF

:process

…

(Revised previous version of this post)

Suggestion: add optional “where” clause to “foreach” statement in C#

Wouldn’t it be nice if I could use in C# the following syntax?

for (SomeType repeaterVariable

      in SomeEnumerable

      where someBooleanExpressionOfRepeaterVariable)

  doSomethingUsingRepeaterVariable;

e.g. use this one:

instead of this one:

BTW, if you wonder what FixTime does, it prepends 0: to time strings to make sure they are of format h:m:s.f

Have added this as a comment to another person’s suggestion that I see has similar format, so please vote for that one:

https://visualstudio.uservoice.com/forums/121579-visual-studio-2015/suggestions/7474789-add-condition-to-foreach-in-statement