diff --git a/Eci.cpp b/Eci.cpp
new file mode 100644
index 0000000..ea6cdb8
--- /dev/null
+++ b/Eci.cpp
@@ -0,0 +1,38 @@
+#include "Eci.h"
+
+Eci::Eci(const Julian &date, const CoordGeodetic &geo)
+: date_(date) {
+
+    static const double mfactor = Globals::TWOPI() * (Globals::OMEGA_E() / Globals::SEC_PER_DAY());
+    const double latitude = geo.GetLatitude();
+    const double longitude = geo.GetLongitude();
+    const double altitude = geo.GetAltitude();
+
+    /*
+     * Calculate Local Mean Sidereal Time for observers longitude
+     */
+    const double theta = date_.ToLMST(longitude);
+
+    const double c = 1.0 / sqrt(1.0 + Globals::F() * (Globals::F() - 2.0) * pow(sin(latitude), 2.0));
+    const double s = pow(1.0 - Globals::F(), 2.0) * c;
+    const double achcp = (Globals::XKMPER() * c + altitude) * cos(latitude);
+
+    position_.SetX(achcp * cos(theta));
+    position_.SetY(achcp * sin(theta));
+
+    position_.SetZ((Globals::XKMPER() * s + altitude) * sin(latitude));
+    position_.SetW(sqrt(pow(position_.GetX(), 2.0) + pow(position_.GetY(), 2.0) + pow(position_.GetZ(), 2.0)));
+
+    velocity_.SetX(-mfactor * position_.GetY());
+    velocity_.SetY(mfactor * position_.GetX());
+    velocity_.SetZ(0.0);
+    velocity_.SetW(sqrt(pow(velocity_.GetX(), 2.0) + pow(velocity_.GetY(), 2.0)));
+}
+
+Eci::Eci(const Julian &date, const Vector &position, const Vector &velocity)
+: date_(date), position_(position), velocity_(velocity) {
+
+}
+
+Eci::~Eci(void) {
+}
diff --git a/Eci.h b/Eci.h
new file mode 100644
index 0000000..a14940a
--- /dev/null
+++ b/Eci.h
@@ -0,0 +1,33 @@
+#ifndef ECI_H_
+#define ECI_H_
+
+#include "Coord.h"
+#include "Vector.h"
+#include "Julian.h"
+
+class Eci {
+public:
+    Eci(const Julian &date, const CoordGeodetic &geo);
+    Eci(const Julian &date, const Vector &position, const Vector &velocity);
+    virtual ~Eci(void);
+
+    Vector GetPosition() const {
+        return position_;
+    }
+
+    Vector GetVelocity() const {
+        return velocity_;
+    }
+
+    Julian GetDate() const {
+        return date_;
+    }
+
+private:
+    Vector position_;
+    Vector velocity_;
+    Julian date_;
+};
+
+#endif
+
diff --git a/Globals.h b/Globals.h
index 47cd589..f74dc7a 100644
--- a/Globals.h
+++ b/Globals.h
@@ -8,6 +8,24 @@ public:
     Globals(void);
     ~Globals(void);
 
+    static const double F() {
+        /*
+         * earth flattening
+         */
+        return 1.0 / 298.26;
+    }
+
+    static const double OMEGA_E() {
+        /*
+         * earth rotation per sideral day
+         */
+        return 1.00273790934;
+    }
+
+    static const double XKMPER() {
+        return 6378.135;
+    }
+
     static const double PI() {
         return 3.14159265358979323846264338327950288419716939937510582;
     }
diff --git a/Observer.cpp b/Observer.cpp
index 40a94c1..b6920f1 100644
--- a/Observer.cpp
+++ b/Observer.cpp
@@ -1,6 +1,19 @@
 #include "Observer.h"
 
-Observer::Observer(void) {
+#include "Globals.h"
+
+/*
+ * in degrees!
+ */
+Observer::Observer(const double latitude, const double longitude, const double altitude) {
+    geo_.SetLatitude(Globals::Deg2Rad(latitude));
+    geo_.SetLongitude(Globals::Deg2Rad(longitude));
+    geo_.SetAltitude(altitude);
+}
+
+Observer::Observer(const CoordGeodetic &geo)
+: geo_(geo) {
+
 }
 
 Observer::~Observer(void) {
diff --git a/Observer.h b/Observer.h
index 26a7936..fee247a 100644
--- a/Observer.h
+++ b/Observer.h
@@ -5,7 +5,8 @@
 
 class Observer {
 public:
-    Observer(void);
+    Observer(const double latitude, const double longitude, const double altitude);
+    Observer(const CoordGeodetic &geo);
     virtual ~Observer(void);
 
     void SetLocation(const CoordGeodetic& geo) {