The blue line determines the height of the two vertical poles. 
With the shown height the shadow of the right pole will pass the foot of the left pole at noon - at equinox. 
Calculate trigonometrically.

December 2002?

East gate 2000  - conceptual design
     The blue line represents the horizon. The same level is marked on the western gate.
     Water is the best medium for levelling, and having a water basin between the 2 gates would be optional, but establishing a Khmer baray on a hilltop is a hard task. A water table to mirror the sun, the moon and the stars, has other astronomical advantages: The line between a mirrored object and the object is straight vertical. And an invisible horizon is situated mid between the objects.
     Distance between the gates = 80 m. and module in bamboo = 1 degree (1.4 m.), so easy to estimate the treetop-horizon to be approximately 1 degree above horizon and the sun approximately 3.5 degrees. March 20 the sun rose at 90*11'32'', three bamboo-sticks before on March 11 at 93*53'50'' - a difference on 3*42'18'' over nine days gives approximately 3 days / stick.
     The golden bamboo stick in the gate marks the shadow of the sun at equinox noon: The equinox stick. It also demonstrates the angle of the rising and setting sun.

     The bamboo sticks in the left part (the northern part) of the gate are pointing towards the Northern Star.

     Simple astronomy with simple tools, and first described in ancient Indian Vedas 2-3 written in the millenniums before Christ. Trigonometry in India is documented to before Christ. Considering the lively contact between India and Angkor it is likely to believe astronomy and trigonometry was well-known in Angkor too.

     The gate was not built, but is considered made with shorter distance between the gates and shorter distance in the 1-degree module-net. Eventually build it together with solstice markers.

     The Solar Gates conceptual design shown above is a proposal to a new Mukdahan landmark, situated on a mountaintop near the Mekhong River facing the river, Laos and the rising sun.
     Boulders marking the solstices will be added. And if sufficient economic basic a water basin between the two gates would be optional.

Time-planning:

1: Setting criteria:
a. Location-specifications: (Altitude: Over tree height. In east-west direction the horizon must be visible (altitude = 0) plus-minus 25 degrees. See drawing Orientation on Solstics in Suan Mali below).
b. Gate width = 1 degree.
c. Determination of orientation (natural / ancient method - as described above and done in Suan Mali).
d. Baray (water basin) between the sun-fences to mirror the rising sun?
e. Structure and composition of working group.

2: Finding location: A location has been proposed on a hilltop facing the Mekhong River south of Mukdahan.

3: Make a sundial (a vertical gnomon to determine equinox days and Vedic determination of east-west).

4: Determination of E-W orientation.
a. Set out an E-W line using Vedic method and compass.
b. Raise two interim gates. 

5: Determination of equinoctial point (preferably at vernal equinox, alternatively at autumnal equinox):
a. Mark the sunrise in the interim gates (and calculate local magnetic deviation).
b. Mark the shadow angle at solar noon (= latitude).
c. Raise Northern Star pole perpendicular to the angle of the shadow in '5b'.

6: Check equinoctial point over a 4-year period in order to make an average. Here the weather is a determining factor: The sun must rise/set with no clouds in the horizon.

7: Final construction in steel and concrete can start. When the orientation is determined the final construction can be finished between two equinoxes. Dimensions, materials, colours etc. are negotiable, but the conceptual design is given by the sun.

8: The construction period will run over 5-6 years and in this period visitors could interactively by either camping on the site at equinox and solstice or follow the project via the Internet: A web camera in each gate could give the whole world access to sunrises over the Mekhong. An associated website about the project could explain basic astronomical ideas and eventual relation to Khmer temples in the region.
     A permanent camp with tents and cottages would be a good idea. The site should be tranquil and with limited use of electricity because stargazing at nighttime is another obvious option.