I played around with Google Earth Pro (it's free!) and was able to get the visualization and the math working.
Visualization:
I created a Line using the Ruler tool (with no regard for were the line was placed). Then I saved the line. Then find the line in your places and right click it and select 'Save Place As...' and save it as a .kml file (not .kmz).
Open the KML file using a text editor and edit the coordinates (near the bottom):

Important to note that the data is entered as degrees longitude, degrees latitude, elevation(units could be only meters or based on your settings).
Save this file and open it in Google Earth Pro. Find the KML file in your places and right click on it and open the properties dialog. GO to the altitude tab and use the drop down menu to select 'Absolute'. This will free the line from the surface. You can then position the camera to look 'down the line' and get a visual sense of the angle above the horizon (and obstructions with 3D buildings on).
Math:
I used Wikipedia's Ellipsoid page to turn a long/lat coordinate to an x,y,z cartesian vector (with the WGS-84 Ellipsoid as the base Earth shape). Note: use the last method shown in the above linked section (i.e., "Measuring angles directly to the surface of the ellipsoid, not to the circumscribed sphere", note that $a=b$ in these formulas).
Once you have the cartesian vectors you can find the angle above the horizon by defining two new vectors:
$V_1=2(\frac{X_{view}}{a^2} , \frac{Y_{view}}{a^2} , \frac{Z_{view}}{c^2})$, the vector normal to the ellipsoid at the viewing point, zenith/up, as described in this answer on the Math Stack Exchange
$V_2=(X_{rocket}-X_{view},Y_{rocket}-Y_{view},Z_{rocket}-Z_{view})$
The angle between these vectors will be the angle between the viewing altitude/elevation and zenith, so its complimentary angle (subtract this value form 90°) will be the altitude/elevation angle. I used the dot product:
$\theta=90°-cos^{-1}(\frac{V_1\cdot{V_2}}{|V_1||V_2|})=-0.0524°$
You will notice; however, from the Google Earth Pro visualization that it appears above the horizon. This alludes to the concept of the local horizon. Sometimes your horizon is more than 90° from zenith because of local topography.
I would suggest finding a better vantage point, but you'll likely need to go a long ways (using the given assumption of rocket location):
Location: |
Elevation Angle |
Cleveland |
1.6° |
Detroit (top of GM building) |
0.23° |
Pittsburgh |
3.5° |
Washington, DC |
7.3° |