From fe27831a2c9ac08b4454fc755d15301f8ad8f392 Mon Sep 17 00:00:00 2001
From: Whitney Armstrong <warmstrong@anl.gov>
Date: Tue, 24 Mar 2020 05:14:49 -0500
Subject: [PATCH] 	modified:   overview.md

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 src/docs/overview.md | 7 +++++++
 1 file changed, 7 insertions(+)

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 title: "Overview"
 ---
 
+## DD4hep 
+
+DD4hep introduces the concept of a `DetElement` which is related to the volumes (logical volumes) and placed volumes but not in a strict way.
+These elements build up a separate tree which describes the relationship between the volumes and the readout detectors. 
+Through the unique BitField ID this allows position space information to be mapped to and from channel number/cell ID space.
+
+![DetElement](DD4hep_block_diagram.svg)
 
 ## EIC Data model
 
-- 
GitLab