adding json

app/controllers/api/users/traces_controller.rb

@@ -7,7 +7,10 @@ module Api
 
       def index
         @traces = current_user.traces.reload
-        render :content_type => "application/xml"
+        respond_to do |format|
+          format.xml { render :content_type => "application/xml" }
+          format.json { render :content_type => "application/json" }
+        end
       end
     end
   end

app/views/api/users/traces/index.json.jbuilder

@@ -0,0 +1,17 @@
+json.gpx_files @traces do |trace|
+  json.id trace.id
+  json.name trace.name
+  json.uid trace.user_id
+  json.user trace.user.display_name
+  json.visibility trace.visibility
+  json.pending !trace.inserted
+  json.timestamp trace.timestamp.xmlschema
+
+  if trace.inserted
+    json.lat trace.latitude
+    json.lon trace.longitude
+  end
+
+  json.description trace.description
+  json.tags trace.tags.map(&:tag)
+end