I would ask for a sample PCAP file, but most people don't want to share real world data. Without a PCAP file, I cannot give you a complete answer, but I can give you one that is 95% there.
This is the way that I would attack your problem:
import pyshark
capture = pyshark.LiveCapture(interface='your_interface')
for raw_packet in capture.sniff_continuously():
# filter only UDP packet that have a frame length greater
# than 190 and that have a port number of 1700.
if hasattr(raw_packet, 'udp') and int(packet.frame_info.cap_len) > 190 and packet[packet.transport_layer].srcport == '1700':
# Get the details for the packets by accessing
# _all_fields and _all_fields.values()
field_names = raw_packet.udp._all_fields
field_values = raw_packet.udp._all_fields.values()
for field_name in field_names:
for field_value in field_values:
# you can add another filter here to get your
# lat & long coordinates
print(f'{field_name} -- {field_value}')
# if you need to access the packet data you need to do this,
# but it might come back in hex, which will need to be decoded.
# if "DATA" in str(packet.layers):
# print(packet.data.data)
Please reach out if you have any issues filtering out the packets that you're looking for. if you can share a sample PCAP, I will tweak my answer.
I have a document and code examples on GitHub named pyshark packet analysis that you might find useful.