Merged in allow_static_models_without_links (pull request gazebosim#626)

Allow static models without links

Approved-by: Ian Chen <ichen@osrfoundation.org>
Approved-by: Eric Cousineau <eacousineau@gmail.com>
Approved-by: Addisu Z. Taddese <addisu@openrobotics.org>

Changelog.md

@@ -43,6 +43,9 @@
 1. sdf 1.7: add `//model/@canonical_link` attribute and require models to have at least one link.
     * [Pull request 601](https://bitbucket.org/osrf/sdformat/pull-requests/601)
 
+1. Static models: allow them to have no links and skip building FrameAttachedToGraph.
+    * [Pull request 626](https://bitbucket.org/osrf/sdformat/pull-requests/626)
+
 1. sdf 1.7: add `//frame/attached_to`, only allow frames in model and world, add Frame DOM.
     * [pull request 603](https://bitbucket.org/osrf/sdformat/pull-requests/603)
 

Migration.md

@@ -199,7 +199,8 @@ but with improved human-readability..
 1. **model.sdf** `//model/@canonical_link` attribute
     + description: The name of the canonical link in this model to which the
       model's implicit frame is attached. This implies that a model must have
-      at least one link, which is also stated in the Modifications section.
+      at least one link (unless it is static), which is also stated in the
+      Modifications section.
     + type: string
     + default: ""
     + required: 0
@@ -210,9 +211,10 @@ but with improved human-readability..
 
 ### Modifications
 
-1.  A model must have at least one link, as specified in the
+1.  A non-static model must have at least one link, as specified in the
     [proposal](http://sdformat.org/tutorials?tut=pose_frame_semantics_proposal&cat=pose_semantics_docs&#2-model-frame-and-canonical-link).
     + [pull request 601](https://bitbucket.org/osrf/sdformat/pull-requests/601)
+    + [pull request 626](https://bitbucket.org/osrf/sdformat/pull-requests/626)
 
 1. Unique names for all sibling elements:
     + As described in the [proposal](http://sdformat.org/tutorials?tut=pose_frame_semantics_proposal&cat=pose_semantics_docs&#3-2-unique-names-for-all-sibling-elements),

src/Model.cc

@@ -259,9 +259,10 @@ Errors Model::Load(ElementPtr _sdf)
     frameNames.insert(link.Name());
   }
 
+  // If the model is not static:
   // Require at least one link so the implicit model frame can be attached to
   // something.
-  if (this->dataPtr->links.empty())
+  if (!this->Static() && this->dataPtr->links.empty())
   {
     errors.push_back({ErrorCode::MODEL_WITHOUT_LINK,
                      "A model must have at least one link."});
@@ -320,21 +321,29 @@ Errors Model::Load(ElementPtr _sdf)
   }
 
   // Build the graphs.
-  this->dataPtr->frameAttachedToGraph
-      = std::make_shared<FrameAttachedToGraph>();
-  Errors frameAttachedToGraphErrors =
-  buildFrameAttachedToGraph(*this->dataPtr->frameAttachedToGraph, this);
-  errors.insert(errors.end(), frameAttachedToGraphErrors.begin(),
-                              frameAttachedToGraphErrors.end());
-  Errors validateFrameAttachedGraphErrors =
-    validateFrameAttachedToGraph(*this->dataPtr->frameAttachedToGraph);
-  errors.insert(errors.end(), validateFrameAttachedGraphErrors.begin(),
-                              validateFrameAttachedGraphErrors.end());
-  for (auto &frame : this->dataPtr->frames)
-  {
-    frame.SetFrameAttachedToGraph(this->dataPtr->frameAttachedToGraph);
+
+  // Build the FrameAttachedToGraph if the model is not static.
+  // Re-enable this when the buildFrameAttachedToGraph implementation handles
+  // static models.
+  if (!this->Static())
+  {
+    this->dataPtr->frameAttachedToGraph
+        = std::make_shared<FrameAttachedToGraph>();
+    Errors frameAttachedToGraphErrors =
+    buildFrameAttachedToGraph(*this->dataPtr->frameAttachedToGraph, this);
+    errors.insert(errors.end(), frameAttachedToGraphErrors.begin(),
+                                frameAttachedToGraphErrors.end());
+    Errors validateFrameAttachedGraphErrors =
+      validateFrameAttachedToGraph(*this->dataPtr->frameAttachedToGraph);
+    errors.insert(errors.end(), validateFrameAttachedGraphErrors.begin(),
+                                validateFrameAttachedGraphErrors.end());
+    for (auto &frame : this->dataPtr->frames)
+    {
+      frame.SetFrameAttachedToGraph(this->dataPtr->frameAttachedToGraph);
+    }
   }
 
+  // Build the PoseRelativeToGraph
   this->dataPtr->poseGraph = std::make_shared<PoseRelativeToGraph>();
   Errors poseGraphErrors =
   buildPoseRelativeToGraph(*this->dataPtr->poseGraph, this);

test/sdf/root_multiple_models.sdf

@@ -7,6 +7,6 @@
     <link name="link"/>
   </model>
   <model name="last_robot">
-    <link name="link"/>
+    <static>true</static>
   </model>
 </sdf>