Fixed problem where SlewToAltAz didn't work correctly. Now uses the RA/Dec slew for everything, and converts the values as needed.

Meade.net.Telescope/AstroMaths.cs

@@ -43,6 +43,53 @@ namespace ASCOM.Meade.net
             return h;
         }
 
+        public double HourAngleToRightAscension(DateTime utcDateTime, double longitude, double hourAngle )
+        {
+            var gst = UTtoGST(utcDateTime);
+            var lst = GSTtoLST( gst, longitude);
+            var raHours = hourAngle;
+            var h1 = lst - raHours;
+            var h = h1;
+            if (h1 < 0)
+            {
+                h += 24;
+            }
+
+            return h;
+        }
+
+        public EquatorialCoordinates ConvertHozToEq( DateTime utcDateTime, double latitude, double longitude, HorizonCoordinates altAz)
+        {
+            var az = DegreesToRadians(altAz.Azimuth);
+            var alt = DegreesToRadians(altAz.Altitude);
+            var lat = DegreesToRadians(latitude);
+            
+            var sinDec = Math.Sin(alt) * Math.Sin(lat) + Math.Cos(alt) * Math.Cos(lat) * Math.Cos(az);
+            var dec = RadiansToDegrees(Math.Asin(sinDec));
+            
+            var y = -Math.Cos(alt) * Math.Cos(lat) * Math.Sin(az);
+            var x = Math.Sin(alt) - Math.Sin(lat) * sinDec;
+            var upperA = Math.Atan2(y,x);
+            var upperB = RadiansToDegrees(upperA);
+
+            var ha = upperB;
+
+            if (upperB < 0)
+            {
+                ha += 360;
+            }
+
+            ha = ha / 15;
+
+            EquatorialCoordinates equatorialCoordinates = new EquatorialCoordinates
+            {
+                RightAscension = HourAngleToRightAscension( utcDateTime, longitude, ha ),
+                Declination = dec
+            };
+
+            return equatorialCoordinates;
+        }
+
         public HorizonCoordinates ConvertEqToHoz(double hourAngle, double latitude, EquatorialCoordinates raDec)
         {
             var h = hourAngle * 15;
@@ -51,7 +98,7 @@ namespace ASCOM.Meade.net
             var lat = DegreesToRadians(latitude);
             var sinA = Math.Sin(d) * Math.Sin(lat) + Math.Cos(d) * Math.Cos(lat) * Math.Cos(h1);
 
-            var y = -Math.Cos(d) * Math.Cos(lat) * Math.Sin(h1);
+             var y = -Math.Cos(d) * Math.Cos(lat) * Math.Sin(h1);
             var x = Math.Sin(d) - Math.Sin(lat) * sinA;
             var upperA = Math.Atan2(y, x);
             var upperB = RadiansToDegrees(upperA);

Meade.net.Telescope/Telescope.cs

@@ -1243,14 +1243,41 @@ namespace ASCOM.Meade.net
 
         public void SlewToAltAzAsync(double azimuth, double altitude)
         {
-            tl.LogMessage("SlewToAltAzAsync", $"Az=~{azimuth} Alt={altitude}");
+            if (altitude > 90)
+                throw new ASCOM.InvalidValueException("Altitude cannot be greater than 90.");
+
+            if (altitude < 0)
+                throw new ASCOM.InvalidValueException("Altitide cannot be less than 0.");
+
+            if (azimuth >= 360)
+                throw new ASCOM.InvalidValueException("Azimuth cannot be 360 or higher.");
+
+            if (azimuth < 0)
+                throw new ASCOM.InvalidValueException("Azimuth cannot be less than 0.");
+
+            tl.LogMessage("SlewToAltAzAsync", $"Az={azimuth} Alt={altitude}");
+
+            HorizonCoordinates altAz = new HorizonCoordinates();
+            altAz.Azimuth = azimuth;
+            altAz.Altitude = altitude;
+
+            var utcDateTime = UTCDate;
+            var latitude = SiteLatitude;
+            var longitude = SiteLongitude;
 
             SharedResources.Lock(() =>
             {
-                TargetAltitude = altitude;
-                TargetAzimuth = azimuth;
+                var raDec = astroMaths.ConvertHozToEq(utcDateTime, latitude, longitude, altAz);
 
-                DoSlewAsync(false);
+                TargetRightAscension = raDec.RightAscension;
+                TargetDeclination = raDec.Declination;
+
+                DoSlewAsync(true);
+
+                //TargetAltitude = altitude;
+                //TargetAzimuth = azimuth;
+
+                //DoSlewAsync(false);
             });
         }