diff --git a/README.md b/README.md
index 403b598..c98b099 100644
--- a/README.md
+++ b/README.md
@@ -86,6 +86,10 @@ implemented (such as obs-ptz uses) as a software daemon.
 * VISCA TCP.
 
 * ONVIF.
+https://github.com/onvif/specs/blob/development/doc/PTZ.xml
+https://github.com/onvif/specs/blob/development/wsdl/ver20/ptz/wsdl/ptz.wsdl
+https://www.onvif.org/specs/srv/ptz/ONVIF-PTZ-Service-Spec.pdf
+https://github.com/BreeeZe/rpos
 
 Other: