diff --git a/src/docs/part2/adding_detectors.md b/src/docs/part2/adding_detectors.md
index 1529eba1bb87af69e5873df61afa189bed89ba81..2fa7f4f69bf3cddd4380983a4db0b8aeefc65a0a 100644
--- a/src/docs/part2/adding_detectors.md
+++ b/src/docs/part2/adding_detectors.md
@@ -2,20 +2,6 @@
title: 'Tutorial Part 2: Modifying and Adding Detectors '
---
- * [Introduction](#introduction)
- * [How to build a detector from scratch](#how-to-build-a-detector-from-scratch)
- + [Compiling a new detector](#compiling-a-new-detector)
- + [Building the geometry](#building-the-geometry)
- - [Compact detector description entry element](#compact-detector-description-entry-element)
- - [Geometry Construction](#geometry-construction)
- * [XML Parsing Tip : Provide good default values](#xml-parsing-tip--provide-good-default-values)
- - [Critical parts of build_detector](#critical-parts-of-build_detector)
- * [The Readout and Bit Fields](#the-readout-and-bit-fields)
- * [Simple Reconstruction Overview of scripts](#simple-reconstruction-overview-of-scripts)
- + [Dependencies](#dependencies)
- + [Running the scripts](#running-the-scripts)
- + [To Do](#to-do)
-
## Setup
Note all these commands assume you are in an `eic-shell` singularity session.
@@ -315,4 +301,157 @@ And have a look at the detector part of the compact file.
Here you see a different strategy: build a module, then build layers constructed from the module.
+Here is the detector constructor function
+```cpp
+static Ref_t create_detector(Detector& description, xml_h e, SensitiveDetector sens) {
+ typedef vector<PlacedVolume> Placements;
+ xml_det_t x_det = e;
+ Material vacuum = description.vacuum();
+ int det_id = x_det.id();
+ string det_name = x_det.nameStr();
+ bool reflect = x_det.reflect(false);
+ DetElement sdet(det_name, det_id);
+ Assembly assembly(det_name);
+ Volume motherVol = description.pickMotherVolume(sdet);
+ int m_id = 0, c_id = 0, n_sensor = 0;
+ map<string, Volume> modules;
+ map<string, Placements> sensitives;
+ PlacedVolume pv;
+
+ assembly.setVisAttributes(description.invisible());
+ sens.setType("tracker");
+
+ // Loop over and build modules
+ for (xml_coll_t mi(x_det, _U(module)); mi; ++mi, ++m_id) {
+ xml_comp_t x_mod = mi;
+ string m_nam = x_mod.nameStr();
+ xml_comp_t trd = x_mod.trd();
+ double posY;
+ double x1 = trd.x1();
+ double x2 = trd.x2();
+ double z = trd.z();
+ double y1, y2, total_thickness = 0.;
+ xml_coll_t ci(x_mod, _U(module_component));
+ for (ci.reset(), total_thickness = 0.0; ci; ++ci)
+ total_thickness += xml_comp_t(ci).thickness();
+
+ y1 = y2 = total_thickness / 2;
+ Volume m_volume(m_nam, Trapezoid(x1, x2, y1, y2, z), vacuum);
+ m_volume.setVisAttributes(description.visAttributes(x_mod.visStr()));
+
+ for (ci.reset(), n_sensor = 1, c_id = 0, posY = -y1; ci; ++ci, ++c_id) {
+ xml_comp_t c = ci;
+ double c_thick = c.thickness();
+ auto comp_x1 = getAttrOrDefault(c, _Unicode(x1), x1);
+ auto comp_x2 = getAttrOrDefault(c, _Unicode(x2), x2);
+ auto comp_height = getAttrOrDefault(c, _Unicode(height), z);
+
+ Material c_mat = description.material(c.materialStr());
+ string c_name = _toString(c_id, "component%d");
+ Volume c_vol(c_name, Trapezoid(comp_x1, comp_x2, c_thick / 2e0, c_thick / 2e0, comp_height), c_mat);
+
+ // use the module vis attributes if not set for component.
+ auto comp_vis = x_mod.visStr();
+ if(( c.visStr().size() >0 ) ) {
+ comp_vis = c.visStr();
+ }
+
+ c_vol.setVisAttributes(description.visAttributes(comp_vis));
+ pv = m_volume.placeVolume(c_vol, Position(0, posY + c_thick / 2, 0));
+ if (c.isSensitive()) {
+ sdet.check(n_sensor > 2, "SiTrackerEndcap2::fromCompact: " + c_name + " Max of 2 modules allowed!");
+ pv.addPhysVolID("sensor", n_sensor);
+ c_vol.setSensitiveDetector(sens);
+ sensitives[m_nam].push_back(pv);
+ ++n_sensor;
+ }
+ posY += c_thick;
+ }
+ // Modules are stored here
+ modules[m_nam] = m_volume;
+ }
+
+ // Construct each layer
+ for (xml_coll_t li(x_det, _U(layer)); li; ++li) {
+ xml_comp_t x_layer(li);
+ int l_id = x_layer.id();
+ int mod_num = 1;
+ for (xml_coll_t ri(x_layer, _U(ring)); ri; ++ri) {
+ xml_comp_t x_ring = ri;
+ double r = x_ring.r();
+ double phi0 = x_ring.phi0(0);
+ double zstart = x_ring.zstart();
+ double dz = x_ring.dz(0);
+ int nmodules = x_ring.nmodules();
+ string m_nam = x_ring.moduleStr();
+ Volume m_vol = modules[m_nam];
+ double iphi = 2 * M_PI / nmodules;
+ double phi = phi0;
+ Placements& sensVols = sensitives[m_nam];
+
+ for (int k = 0; k < nmodules; ++k) {
+ string m_base = _toString(l_id, "layer%d") + _toString(mod_num, "_module%d");
+ double x = -r * std::cos(phi);
+ double y = -r * std::sin(phi);
+ DetElement module(sdet, m_base + "_pos", det_id);
+ pv = assembly.placeVolume(m_vol,
+ Transform3D(RotationZYX(0, -M_PI / 2 - phi, -M_PI / 2), Position(x, y, zstart + dz)));
+ pv.addPhysVolID("barrel", 1).addPhysVolID("layer", l_id).addPhysVolID("module", mod_num);
+ module.setPlacement(pv);
+ for (size_t ic = 0; ic < sensVols.size(); ++ic) {
+ PlacedVolume sens_pv = sensVols[ic];
+ DetElement comp_elt(module, sens_pv.volume().name(), mod_num);
+ comp_elt.setPlacement(sens_pv);
+ }
+
+ if (reflect) {
+ pv = assembly.placeVolume(
+ m_vol, Transform3D(RotationZYX(M_PI, -M_PI / 2 - phi, -M_PI / 2), Position(x, y, -zstart - dz)));
+ pv.addPhysVolID("barrel", 2).addPhysVolID("layer", l_id).addPhysVolID("module", mod_num);
+ DetElement r_module(sdet, m_base + "_neg", det_id);
+ r_module.setPlacement(pv);
+ for (size_t ic = 0; ic < sensVols.size(); ++ic) {
+ PlacedVolume sens_pv = sensVols[ic];
+ DetElement comp_elt(r_module, sens_pv.volume().name(), mod_num);
+ comp_elt.setPlacement(sens_pv);
+ }
+ }
+ dz = -dz;
+ phi += iphi;
+ ++mod_num;
+ }
+ }
+ }
+ pv = motherVol.placeVolume(assembly);
+ pv.addPhysVolID("system", det_id);
+ sdet.setPlacement(pv);
+ return sdet;
+}
+
+// clang-format off
+DECLARE_DETELEMENT(TrapEndcapTracker, create_detector)
+DECLARE_DETELEMENT(MyGEMTrackerEndcap, create_detector)
+```
+
+
+
+
+## Hands on challenges
+
+### Update gem tracker
+
+Swap out the gem tracker from part 1 with the detailed construction.
+
+### Add top and bottom support for the GEM foil frame.
+
+There is a side currently there
+
+### Make the modules overlap
+
+Currently the modules do not overlap much. Can you come up with a way to modify to get a nice overlap?
+
+### What bug exists with the negative endcap?
+
+If you uncomment the negative endcap, can you find out what is wrong with the construction?
+