Reduce number of waypoints in route?

[wholybee]

Is there a way to reduce the number of waypoints in a route? Something that would reduce the points based on an acceptable crosstrack error, vs just removing them at a time interval.

[nohal]

Warren...
Do you really speak about routes (= The manually created plan of where you would like to go, which usually has waypoints only in places where the author, a human, decided to place them)? If yes, there is no such automatic logic to change them as we anticipated the author knew what he's doing.

There is a simplification logic for recorded tracks, doing pretty much what you describe, accessible by right-clicking a track in the route and waypoint manager. It is simple to convert a route to track by editing a GPX file in a decent text editor. The reverse - generating a route from track, is directly possible in OpenCPN.

I would like to see a route that needs such treatment to understand your need better.

Pavel

[wholybee]

The specific need is for routes created by weather routing. If I recall (not on boat right now) those are first created as tracks, so this should work for me. Thank you.

I would also like to do the same for a great circle route created by the route plugin. If that isn't created as a track, I can edit the gpx file.

[nohal]

Originally Posted by wholybee

The specific need is for routes created by weather routing. If I recall (not on boat right now) those are first created as tracks, so this should work for me. Thank you.

I would also like to do the same for a great circle route created by the route plugin. If that isn't created as a track, I can edit the gpx file.

Well, for routes created by weather routing that should probably be done by weather routing plugin during the actual routing process to maintain accuracy of the calculations...

[rgleason]

In wxroute, pick Export. It exports to Track manager. Figure out which route in Track manager. The right click and pick "Reduce Data"


Not having much luck with the Great Circle Route Plugin by saltypaws. Can't seem to import a gpx of its route into route and track manager.



I am able to make a great circle route with the built-in route functions. I suppose you could remove wpts from that easily enough. I was trying to export that as a track but there is not adequate data so it just exports a gpx that when imported is brought into the route tab. I guess there is no way to convert it to a route and then reduce data.

[Tupaia]

Originally Posted by rgleason

Not having much luck with the Great Circle Route Plugin by saltypaws. Can't seem to import a gpx of its route into route and track manager.

I am able to make a great circle route with the built-in route functions. I suppose you could remove wpts from that easily enough. I was trying to export that as a track but there is not adequate data so it just exports a gpx that when imported is brought into the route tab. I guess there is no way to convert it to a route and then reduce data.

This only becomes relevant if you manually sail the GC route. For example if you +/- an electronic pilot or use a wind vane type steering system. Most integrated AP/GPS's sail GC routes by default (check in your GPS settings). So if your AP is sailing to a WP it will adjust accordingly. Any extra WP's introduced are therefore unnecessary. The integrated approach is far superior especially in areas where there is large magnetic variation that changes throughout the journey.

To prove this create a route in OCPN where GC is relevant and it will plot the intermediate WP's (150-220Nm apart). Set the AP to sail to the last WP and it will track through each of the intermediate WP's. Your compass heading will constantly change to cope with the GC routing and the variation.

Also for long passages it is better to know how far you have to go rather than the distance to the next intermediate WP.

[rgleason]

is no way to convert it to a route and then reduce data.

I meant convert it to a Track and then reduce data.

Thanks Tup, those are interesting points, but then you wouldn't use GC routing, just rhumline. I am not so sure my 23 year old autohelm wheelpilot knows Great Circle.

I was just seeing about O functionality.

[Tupaia]

Originally Posted by rgleason

I meant convert it to a Track and then reduce data.

Thanks Tup, those are interesting points, but then you wouldn't use GC routing, just rhumline. I am not so sure my 23 year old autohelm wheelpilot knows Great Circle.

I was just seeing about O functionality.

Your raymarine autopilot, however old it may be, if linked to GPS, does sail a great circle route with a constantly changing heading if you ask it to steer to a destination waypoint. This applies to any wp even one a very short distance away.

The main difference between GC and RL is that it is impossible for humans and wind vanes to steer a GC because the bearing will constantly change. Also you need a gnomic projection chart to lay off a GC route and most charts are mercator hence you end up with a RL.

If you select GC in OCPN all it does is plot a GC route on a mercator chart. The result is a segmented route with a different bearing for each leg.

So using a GC plot on OCPN is only of any use if you intend to sail manually, or by wind vane to a compass bearing. I suppose on a very long passage it would also allow you to make sure that a GC doesn't cause you to hit anything slightly off of the RL.

If you are using a GPS and are intending to ask your AP to steer to a WP then simply enter a single WP at your destination and it will by default sail a GC route.

[rgleason]

Originally Posted by Tupaia

Your raymarine autopilot, however old it may be, if linked to GPS, does sail a great circle route with a constantly changing heading if you ask it to steer to a destination waypoint. This applies to any wp even one a very short distance away.

The main difference between GC and RL is that it is impossible for humans and wind vanes to steer a GC because the bearing will constantly change. Also you need a gnomic projection chart to lay off a GC route and most charts are mercator hence you end up with a RL.

If you select GC in OCPN all it does is plot a GC route on a mercator chart. The result is a segmented route with a different bearing for each leg.

So using a GC plot on OCPN is only of any use if you intend to sail manually, or by wind vane to a compass bearing. I suppose on a very long passage it would also allow you to make sure that a GC doesn't cause you to hit anything slightly off of the RL.

If you are using a GPS and are intending to ask your AP to steer to a WP then simply enter a single WP at your destination and it will by default sail a GC route.

Thanks for that Good, information. I hadn't thought at all about this. I wonder if there is a place for it in the manual? What would we call it? Where would it fit? How about
"GPS and Autopilots following Great Circle Routes"?