mavextra: error in distance estimation

[gitdillo]

I think there is an error in distance estimation in mavextra's distance_lat_lon().

Specifically, latitude and longitude are converted to radians only when taking their difference:

    dLat = radians(lat2) - radians(lat1)
    dLon = radians(lon2) - radians(lon1)

but then the code mixes up radians and degrees when using the difference (in radians) or the actual values (in degrees), i.e.:

    a = sin(0.5*dLat)**2 + sin(0.5*dLon)**2 * cos(lat1) * cos(lat2)
    c = 2.0 * atan2(sqrt(a), sqrt(1.0-a))

In the bit above, dLat and dLon are in radians while lat1, lat2 are in degrees.

Ideally, the conversion should happen to the inputs immediately, as it happens for example in distance_from().

[gitdillo]

For example, this works:

def distance_lat_lon(lat1, lon1, lat2, lon2):
    '''distance between two points'''
    lat1 = radians(lat1)
    lon1 = radians(lon1)
    lat2 = radians(lat2)
    lon2 = radians(lon2)
    dLat = lat2 - lat1
    dLon = lon2 - lon1

    a = sin(0.5*dLat)**2 + sin(0.5*dLon)**2 * cos(lat1) * cos(lat2)
    c = 2.0 * atan2(sqrt(a), sqrt(1.0-a))
    ground_dist = 6371 * 1000 * c
    return ground_dist

[khancyr]

@gitdillo yes that an error. The function is unsafe on lat/long wraping too.
Could you make a PR to update it like https://github.com/ArduPilot/MAVProxy/blob/d43ee6396f3b38d2c2049adc86ccd65b9b661250/MAVProxy/modules/lib/mp_util.py#L42 and maybe put a comment to this function on mavproxy that is more maintained ?

[gitdillo]

Hello Pierre, I don't really know how to do that, if you know, could you please do it?

…

On Fri, 25 Feb 2022 at 09:46, Pierre Kancir ***@***.***> wrote: @gitdillo <https://github.com/gitdillo> yes that an error. The function is unsafe on lat/long wraping too. Could you make a PR to update it like https://github.com/ArduPilot/MAVProxy/blob/d43ee6396f3b38d2c2049adc86ccd65b9b661250/MAVProxy/modules/lib/mp_util.py#L42 and maybe put a comment to this function on mavproxy that is more maintained ? — Reply to this email directly, view it on GitHub <#635 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAE27GWCZWOCBXQUS4BJII3U446VTANCNFSM5OMLHWGA> . Triage notifications on the go with GitHub Mobile for iOS <https://apps.apple.com/app/apple-store/id1477376905?ct=notification-email&mt=8&pt=524675> or Android <https://play.google.com/store/apps/details?id=com.github.android&referrer=utm_campaign%3Dnotification-email%26utm_medium%3Demail%26utm_source%3Dgithub>. You are receiving this because you were mentioned.Message ID: ***@***.***>