GPS combo to use when running in forest / dense area.

I might be wrong but you probably should use GPS + GLONASS or GPS alone.  Belgium is on the 50 degree line of latitude and apparently Galileo works best when below the 40 degree line.  

1) I don't think it is that easy to say which is best to use. It varies from day to day (actually minute for minute) since the satellites are moving. It is hard for the GPS system to work in dense forest. What you could do it to use GPS Soaking before you start. It means that you wait for a couple of minutes extra after you get the green GPS before you start. 

2) Use a heart rate strap.

I use GPS + GLONASS i live in the Netherlands (so should be similar) In the forest i always a foot pot for the most accurate pace. Although GPS works fairly aswel. Happy Running

1) use the combination that leads to the maximum number of satellites available (at the moment could be GPS+GLONASS, GALILEO constellation is a little bit underperforming); anyway, every GNSS combination available will be wrong in instant pace under heavy foliage/trees; the only way to achieve a good trail instant pace is the use of a well calibrated footpod (Garmin, Stryd or - my choice - RunScribe).
2) if you plan to do trainings with heart short, fast and deep variations, then use an heart strap. at the moment any short fast run fartlek sequence will be "lost" with optical reading cardio.

Thank you for the advise. 

Regarding the GPS, letting it soak in is something i'll definitely try next time. 

Thanks. I'll use that combo next time and check if that gives an accurate reading. 

Good to know. I would've thought the galileo system would be the best combination since it's newer and according to their site now fully deployed.

But i didn't know that about the latitude that it could make a difference. Thanks

Since most of you think the best combination would be GPS+GLONASS and not GALILEO, i'll use that for my next run. 

I understand what you're suggesting about the footpod giving the best continuous results regarding pace, even in forests. 

However, When i bought the Forerunner 945; My thinking was that the 945 (which is a Garmin top model compared to the vivoactive 3 music) will give better results. Both regarding pace and heart rate.   

Which would mean i am expecting my 945 to give better results regarding the correct pace when running in a forest or under trees when i compare it to my previous model vivoactive 3. Or at least that my 945 will correct itself after i conclude the run or exit the forest so that the pace is recalculated when saving my run. So that my run in the forest gives a correct result.

--<(A bit like a cheap phone vs an expensive model. It all does quit the same, but the top model will give you more precise and better results.) 

Was my thinking regarding that manner wrong? I would expect a top model to give more precise results vs a cheaper and older model. Even when running in such environments. 

Thank you

try thi simple tool to have a clear view about how many satellites are available in a location in a defined timespan (tip: use a reasonable elevation cutoff (15/20° or more), all GNSS ssatellites below this angle are usable only in a professional controlled environment with proper antennas
https://www.gnssplanning.com

every Garmin watch, even top or expensive, can't overrule the physical limits of GNSS systems (every precision/accuracy increase will affect unreasonably battery life)

Meh, sensors used will remain the same most of the time though... 

With the 945 you get a more highend watch wrt features, battery, sturdiness, functionality, maps. Not necessarily better sensors.

For HR I nowadays use a Polar OH1+, while previous OHR used to work pretty fine for me with at least steady runs the 945 is less forgiving. As I now train based on HR and also many intervals are involved the OHR just didn't cut it anymore. It's partly consequence of the technology and sometimes it just doesn't work will with someone.

GPS, I always use just GPS actually (Netherlands) but might give GPS+GLONASS a try. I run in farily open areas most of the time and GPS is spot on, but indeed notice flakiness when running in forests. Then again, if the view is obstructed I can't imagine using more satelistes would help THAT much. Again, consequence of technology.