"David Dunham" wrote:
> For higher elevations, the path will shift southwest by approximately the height above sea level, that
> effect not taken into account with the interactive plots.

Indeed - however it is easy to take "elevation" into account when using the interactive maps.

To show folks how to do 'site planning' from half way round the world with just a few mouse clicks - here is a worked example for this event: "Grazing Occultation of 1251 B9 Magnitude 5.9 lamda Cancri, May 4th 2006"

Let's assume I am to be near Santa Barbara (CA) and restricted (by weather) to high ground, so a trip up Lockwood Valley Road is planned. It is decided to go 1.0 Km 'south' of the graze limit line. 

(ED Note- Determining this “Observing Zone” is dependant on the profile at the expected observing Longitude. If you do not have WinOCCULT (or similar) to examine and determine the observing zone, email Derek for help – Derek)

Using the interactive map that Derek has provided at:
http://www.poyntsource.com/New/Google/May4_graze.htm

I zoom into the gray line that is set to -1Km on Lockwood Valley Road.

Clicking the TOPO button on the map will allow you to find the height of the observing location is about  5,200 feet.

The TanZ value for this graze is 1.01 (at -119 longitude), so the amount of horizontal shift is 1,585 x 1.01 = 1,600 metres parallel to the GREEN line on the map.

Because it is a northern graze, the graze line is moved 1,600 metres 'south', parallel to sea level graze line. Because Derek's map is at sea level (ok 14 metres) then we need to shift our (-1 km) gray line 1.6 Km further to the south.

Setting the gray line to -2.6 on the interactive map, we zoom in, on the WEST side of the road (Moon is at 271 azimuth, 45 elevation) gives the following coordinates: "at = 34.719502, Lon = -119.112858, which is 2.6 Km from graze limit line" - which will place us 1 Km south of the (altitude corrected) limit line.

We have also derived the coordinates to put into a GPS to take us to the correct roadside position. We can also see from the high resolution imagery of the interactive map, that there are no obstructions to the west (like trees etc).

So as you can see, site planning can be done with these interactive maps from a long distance away (and be fun) - even if the site is at high altitude!

Regards, Kiwi Geoff (New Zealand).