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Re: [Paparazzi-devel] SRTM and keeping a certain distance above groud le

From: Rokas Adiklis
Subject: Re: [Paparazzi-devel] SRTM and keeping a certain distance above groud level for all waypoints
Date: Sun, 25 Apr 2010 00:43:09 +0300

Hi Nathan,

I'm just a noob here, but here's my guess:

SRTM is used only as a reference for the user to know what heights to expect in a certain area, when designing a flight plan. It is only used to DISPLAY the height of the point on the map under the mouse cursor.

This is how I use it: let's say tomorow I'll be flying in a new location and I want to create a custom flight plan for it. First I copy/paste some favorite plan and change it's initial coordinates to the desired ones (of that new location, read form Google Earth). Next thing I do is I load that plan into PPZ and download map photos form google to get a better visual understanding. Then I download SRTM data and enable it. Finally I move my mouse over the map to see the estimated heights AGL (above ground level), and find a perspective location for takeoff/landing. Then I enter this data (height) in my flight plan as "ground_alt" and use it as a reference. Also, it might help determining safe/default waypoint height, it the place if not flat. However, if I design the flight plan "on site", I don't need SRTM because I can see live (and theorically more precise) data from onboard GPS while the plane is on the ground (our country is pretty much flat...).

Now, about flying at constant height AGL - PPZ would have to store all the SRTM data onboard to accomplish that, and I really doubt that it does. The only way to achieve it (I can think of) is to drag your mouse over the flight path and if you see major differences in height AGL (SRTM data), just add additional waypoints to match the height curve.

Accept this info only as a noobs opinion and don't take it for a fact, as I am way too "young" in this whole PPZ thing. And please correct me where I'm wrong. Thanks.

Rokas Adiklis

On Sat, Apr 24, 2010 at 10:41 AM, Nathan Aherne <address@hidden> wrote:

I am pretty sure this question is answered in the wiki but I am not quite getting the concept. Using the SRTM data I would like to keep a certain height above ground level. When I set the waypoint heights I just assumed they were heights above ground level based on what SRTM data says for instance if the ground height at a particular way point is 400m and the way point height is set to 90 then the aircraft would be at 490m when hitting that way point. It seems that the height of each way point is the heights above the ground level you set in the first line of the flight plan. I would like to be able to set the ground level heights to height above ground level.

I don't think I am getting the concept of using the SRTM data and how to use that to stay above a certain height. Would someone mind giving me a bit of a conceptual rundown of how to use the SRTM data effectively?

Kindest regards,

Nathan Aherne
Reddog Technology
Email: address@hidden
Mob: 0402 555 080

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