Support setting canonical link

[claireyywang]

Set canonical link if defined in sdformat file, otherwise set first link of model as canonical. Closes #100

[claireyywang]

[Resolved]
I have some questions related to nested model @iche033 @scpeters

1. Do each model (nested or not) only have one canonical link or each nested model can have its own canonical link?
2. If a model doesn’t have a top level link, does it take the nested model’s first link as the canonical link?

So far I only added a generic function in Model.cc and let SdfFeatures.cc set the canonical link since that's when we can determine whether CanonicalLink is defined or not for a model. I'm not sure if canonical link canbe set at Model::AddLink() due to limited information about a link (whether I should set first link or defined <canonical_link>).

[iche033]

thanks for the changes. I have a couple minor comments, and one about adding a test to verify canonical link in a nested model

[iche033]

Just a couple of minor code check issues. I added some checks in SDFFeatures_TEST and tests pass. Feel free to incorporate these changes

diff --git a/tpe/plugin/src/SDFFeatures_TEST.cc b/tpe/plugin/src/SDFFeatures_TEST.cc
index bbef33f..78cd972 100644
--- a/tpe/plugin/src/SDFFeatures_TEST.cc
+++ b/tpe/plugin/src/SDFFeatures_TEST.cc
@@ -37,6 +37,7 @@
 #include <ignition/physics/sdf/ConstructWorld.hh>
 
 #include "lib/src/Entity.hh"
+#include "lib/src/Model.hh"
 #include "lib/src/World.hh"
 #include "World.hh"
 
@@ -413,6 +414,12 @@ TEST(SDFFeatures_TEST, NestedModel)
       nestedCollision.GetId());
   EXPECT_EQ("nested_collision", nestedCollision.GetName());
   EXPECT_EQ(ignition::math::Pose3d::Zero, nestedCollision.GetPose());
+
+  // canonical link
+  ignition::physics::tpelib::Model *m =
+      static_cast<ignition::physics::tpelib::Model *>(&model);
+  ignition::physics::tpelib::Entity canLink = m->GetCanonicalLink();
+  EXPECT_EQ(link.GetId(), canLink.GetId());
 }

[codecov]

Codecov Report

Merging #142 (13ef221) into ign-physics2 (c11a47d) will increase coverage by 0.04%.
The diff coverage is 96.15%.

@@               Coverage Diff                @@
##           ign-physics2     #142      +/-   ##
================================================
+ Coverage         83.06%   83.10%   +0.04%     
================================================
  Files               106      106              
  Lines              3973     3983      +10     
================================================
+ Hits               3300     3310      +10     
  Misses              673      673              

Impacted Files	Coverage Δ
tpe/plugin/src/FreeGroupFeatures.cc	79.68% <66.66%> (-0.32%)	⬇️
tpe/lib/src/Model.cc	98.36% <100.00%> (+0.02%)	⬆️
tpe/plugin/src/SDFFeatures.cc	84.24% <100.00%> (+1.15%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update c11a47d...13ef221. Read the comment docs.