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Magnetic Anomalies?

AMann

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#1
How much could this area north of San Francisco mess up your flight? Appears to have some magnetic ground anomalies - sectionals warn as much as 8 degrees off.

Its another reason why everyone should look at sectionals before flying, not just the usual apps.

EAED0554-71F6-404C-8F9E-0952E8EC911F.jpeg
 
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Meta4

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#2
How much could this area north of San Francisco mess up your flight?
Are you intending to fly a precise compass course like a yacht might to clear some offshore rocks or stay in a channel?
You normally have no idea what course you are flying, so having a course bearing off by 7 degrees won't make any difference at all to your flying.
 
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#3
How much could this area north of San Francisco mess up your flight? Appears to have some magnetic ground anomalies - sectionals warn as much as 8 degrees off.

Its another reason why everyone should look at sectionals before flying, not just the usual apps.

View attachment 66193
I bet most pilots dont even think about this. 8° off could definitely give you a compass calibration error, and possibly a flyaway, especially the further away you fly from your home point.

8° might not seem like much, but the Mavic uses both GPS and compass (2 compasses in the MP), and they are already super sensitive to interference. Add an 8° variation, and the Mavic might have a hard time figuring out which course to take or which way to point.

For those who only calibrate once in the life of their drone, this is a good reason to not ignore the error message. If you calibrate in New York, then pay a visit to Point Arena, who knows what is going to happen if the compass is confused.
 
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Meta4

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#4
I bet most pilots dont even think about this. 8° off could definitely give you a compass calibration error, and possibly a flyaway, especially the further away you fly from your home point.

8° might not seem like much, but the Mavic uses both GPS and compass (2 compasses in the MP), and they are already super sensitive to interference. Add an 8° variation, and the Mavic might have a hard time figuring out which course to take or which way to point.

For those who only calibrate once in the life of their drone, this is a good reason to not ignore the error message. If you calibrate in New York, then pay a visit to Point Arena, who knows what is going to happen if the compass is confused.
Actually this would not have any effect at all for drone flyers and would not require calibration at all.

The magnetic anomaly just means that the magnetic variation there is different from what is observed in the surrounding area.
Calibration has nothing to do with the local magnetic variation which changes all over the world.
The only thing compass calibration does is to measure the magnetic fields that are part of the drone so they can be ignored.
Calibration of the compass in NY won't be any different from calibration anywhere else in the world.
 
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#5
... and calibration requires a positionally homogeneous local magnetic field whose direction is irrelevant. That’s why during calibration you don’t have to start at the any specific direction, like North. And you should not be near other magnetic influences that have a short range affect as you rotate the quad. The field needs to be horizontal and consistent within the range of motion during calibration.

The older members may remember the calibration procedure for a compass in a car. You had to drive around in a circle in a parking lot. Sound familiar? Made me dizzy!
 
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AMann

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#6
Actually this would not have any effect at all for drone flyers and would not require calibration at all.

The magnetic anomaly just means that the magnetic variation there is different from what is observed in the surrounding area.
Calibration has nothing to do with the local magnetic variation which changes all over the world.
The only thing compass calibration does is to measure the magnetic fields that are part of the drone so they can be ignored.
Calibration of the compass in NY won't be any different from calibration anywhere else in the world.
But the anomaly is in a tight area- right along the beach. I am not sure if it is ferrous containing sands or a formation under it and am looking for geologic maps of that area to see. So someone who calibrates their compass on the beach and walking over during flight to a close location like the bluffs just inland from it and landing there may be off quite a bit, as may someone who programs a waypoint flight and intends to aim the gimbal in specific directions for shooting the coastline.

Its an interesting scenario and place, geologically speaking. My curiosity about such anomalies is because I like geology and started to notice olacesmlikenthisnon the sectionals and wondered what flying through them would do.
 
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Meta4

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#7
But the anomaly is in a tight area- right along the beach. I am not sure if it is ferrous containing sands or a formation under it and am looking for geologic maps of that area to see. So someone who calibrates their compass on the beach and walking over during flight to a close location like the bluffs just inland from it and landing there may be off guite a bit.
No ... you are assuming that compass calibration is affected by magnetic issues in the local environment when it is only concerned with measuring the magnetic fields that are part of the drone itself.
Read post #2 again.
 

AMann

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#8
No ... you are assuming that compass calibration is affected by magnetic issues in the local environment when it is only concerned with measuring the magnetic fields that are part of the drone itself.
Read post #2 again.
If someone calibrates from within the anomaly, won’t it be off when the drone flies out of the affected area? Its a tight area on the shoreline and can be easily traversed during a flight. 8 degrees is a lot- it would be the same thing as calibrating in Los Angeles and not recalibrating while flying it in Corpus Cristi, almost 1500 miles away.
 
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AMann

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#9
I guess the bright side is that you could be calibrated for flying in two distant places at once, in the anomaly area at Point Arena, CA, and at the same time 1500 miles east towards San Antonio, or 1500 west towards Hawaii, by calibrating the drone at Point Arena :)
 
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#10
If someone calibrates from within the anomaly, won’t it be off when the drone flies out of the affected area? Its a tight area on the shoreline and can be easily traversed during a flight. 8 degrees is a lot- it would be the same thing as calibrating in Los Angeles and not recalibrating while flying it in Corpus Cristi, almost 1500 miles away.
That's what I was thinking but I am by no means a magnetic field physicist.
 
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AMann

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#11
That's what I was thinking but I am by no means a magnetic field physicist.
Ok, but magnetic declination is easy to understand... anyways, I always thought calibration was just to align the azmith of the drone body (compass board) to magnetic north innorder to get a proper declination for true north for the map to work correctly. The way that its explained in post #2, it sounds like compensating for the drone’s body only- but that adjustment only needs to be done once, much like the metal compensators on a ship compass.
 

Meta4

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#12
Ok, but magnetic declination is easy to understand... anyways, I always thought calibration was just to align the azmith of the drone body (compass board) to magnetic north innorder to get a proper declination for true north for the map to work correctly.
Compass calibration is unrelated to geographic location, magnetic declination etc.
The way that its explained in post #2, it sounds like compensating for the drone’s body only- but that adjustment only needs to be done once, much like the metal compensators on a ship compass.
That's a perfect analogy for what compass calibration does.
The drone and its electrical equipment have magnetic fields.
It's important for the compass to be reading the earth's magnetic field and not the Mavic's so the drone's magnetic field is measured and that can be subtracted from the total magnetic field measurement.
 

AMann

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#13
Compass calibration is unrelated to geographic location, magnetic declination etc.

That's a perfect analogy for what compass calibration does.
The drone and its electrical equipment have magnetic fields.
It's important for the compass to be reading the earth's magnetic field and not the Mavic's so the drone's magnetic field is measured and that can be subtracted from the total magnetic field measurement.
So I’m thinking of this from an old salty background when compasses didnt need batteries and there were steel compensators on them to adjust for the affects of the boat or car body on the magnetic field. That adjustment only hadnto be done once and the pilot would use magnetic north for bearings, so declination didn’t matter.

But as the software asks for a recalibration every time one moves very far, why does it ask for it then vs flying in the same area over a few days? I really see it as a alignment of the body to mag north so it can tell which way its pointing in a yaw. If one does not recalibrate, the map will be off as will navigation.

Thanks for your help trying to explain it, I really like anything to do with navigation and find it all interesting - hence why I was looking for anomalies on the sectionals.

I also found a slot canyon once where GPS was always off if you could get it by 100yards- the tightness of the canyon, it’s N/S orientation and it’s granite signal reflecting walls were terrible for navigation.
 
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Meta4

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#14
But as the software asks for a recalibration every time one moves very far, why does it ask for it then vs flying in the same area over a few days? I really see it as a alignment of the body to mag north so it can tell which way its pointing in a yaw. If one does not recalibrate, the map will be off as will navigation.
DJI can be a bit odd with some of their communication and documentation.
They confused everyone by saying in their early manuals that you should recalibrate the compass at each new flying location.
It turned out that this was not at all necessary but it wasn't until the P4 pro about 2.5 yrs ago that DJI finally updated their manual to delete that instruction.
But when they brought out the Mavic 2, for some unknown reason they have programmed it to ask for a compass calibration if you move a certain distance from the last calibration or if it's >30 days.
The smart people still can't work out why since there is no technical reason for this.
I've been flying a P4 pro for 2.5 yrs including lots of travel, even overseas, all without ever calibrating anything.
It still flies as well as it did on day one straight out of the box.
 
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AMann

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#15
”Im careful about applying any extra metallic objects anywhere around the compass.”
I put this question on this post as it’s sort of topic related - In the above post, you mentioned putting metalic items (a 360 camera) near the compass. To avoid doing this myself, where exactly is the Compass board on a M2P? Is it foreward of the GPS antenna?
 
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AMann

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#16
I put this question on this post as it’s sort of topic related - In the above post, you mentioned putting metalic items (a 360 camera) near the compass. To avoid doing this myself, where exactly is the Compass board on a M2P? Is it foreward of the GPS antenna?
The reason I’m curious is that I’d like to do something like this with a IR modified GoPro too:

30933D85-0695-4A35-AAC1-A28123CC90DB.gif
 
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