cechner's comments

actually, beta is less useful than that! I think it represents the median difference between the two distances, its not a tolerance (at least as far as I can recall after experimenting with tuning this value).

As with you, I have found that it still often gives ok results with slower frequencies, as long as the transition probabilities are still relatively in the same scale as each other for a particular observation pair. However it means that there's no point trying to 'tune' using the gamma and beta parameters

it should be in seconds - the problem is that the paper assumes that the 'great circle' (straight line) distance between two points should be almost the same as the 'route' distance between those points, with an exponential probability distribution.

This means that if the path between two points is not simple (around a corner) the probability drops off very quickly. If the time between measurements is in minutes, this heuristic is pretty useless (and you should really use log-scale for your numbers!)

edit: this is actually shown in figure 8 of the paper where they explore different 'sampling periods'

edit 2: I have not explored other methods yet, but it would probably make sense to start by deriving the formula the way they do, by exploring ground-truth data.

edit 3: I just noticed that my comments are largely repeating what you're saying - sorry!

yep - look up 'Hidden Markov Map Matching through Noise and Sparseness' by Krumm and Newson

it calculates the final probability by combining 'emission' probabilities (the probability that a GPS observation was on a particular road) by the 'transition' probability that if an observation was on a particular road at one point, what is the probability that it is now on this other road segment. By combining these two the final probability incorporates both the nearness of the GPS signals to the roads and the connectivity of the road network itself.

I've found the formulas applied in this paper are good in practice only if the GPS updates are relatively frequent

do you have more modern benchmarks that cover the same ground?

what is the point of this headline, other than to decieve? it is not the headline of the article and is not a quote from the text in the article

edit: I hope I'm not just being a killjoy here - I actually thought this was going to be some kind of political article.

When I first used Parallels years ago I was pretty surprised how close to native it could run Windows (though not 3D graphics intensive apps, as far as I can recall.)

I tried running it recently though and the performance was _abysmal_. Just unusable, taking 30 minutes just to boot into a Windows 10 machine. I can fully believe that the problem is with some major change in OSX or Windows or something, but I feel ripped off for having paid for it again.

(yes, I tried all the little hacks and tricks from the forums.)

> Developers do need to pick a set of core technologies, and stick to it or a career can fall apart I bet

I hope not for my sake :) Im currently contracting writing C++, but my previous contract was with the ASP.Net stack. Before that I was working on a lot of Java services (introduced Scala to good effect)

I also have started a side business helping small companies by making small apps helping with their everyday stuff - sometimes Ill make iPad apps with Swift, but more recently Qt/QML to make something that runs on both OSX and Windows desktops natively. I also made (very small!) web apps for them hosted on both Azure (MS stack) and AWS (linux stack)

After a while learning the core aspects of a new language doesn't take very long, and they generally have to address the same high-level concerns. That said, learning iOS development was a continual hassle but feels like it was worth it to have a native app that I can deploy easily using HockeyApp etc.

edit: I will undermine my whole point here by saying that I abandoned a personal Android project because the dev environment felt so ad-hoc and duct-taped. I spent a ridiculous amount of time trying to get the simulator to render GL properly without any luck (on Windows)

holy moly, I have forgotten more than I realised :( embarrassing

nah thats mitsu (as in mitsubishi)

(I went to bed so didn't take long to reply before)

I am clearly not expressing myself well. I am talking about a situation where some stakeholders are expecting a complete picture of roughly how large the project is and would like to be able to track how far your team is through this project on a regular basis.

I am putting scrum forward as a methodology for, in as short a time as possible, measuring the size of that project in a meaningful way by merely breaking it up into as small pieces as possible and attaching numbers to those pieces, intended to measure the size of each piece relative to the other pieces, and then over time discovering how long it takes to complete a piece of a given size.

> Assume each person giving different estimates for their own work, but not up front - ongoing as code is written.

The situation I outlined above (the time when scrum helps out) requires you have a stab at estimating all the constituent parts of the project at the beginning of the project.

> an estimate is an estimate, not a commitment. Committing to an estimate makes it a commitment, not an estimate.

True, but the point of estimating in scrum is to assign relative sizes to the pieces of work, not a number of hours, so this isnt a commitment to finish at a specific time but just to say 'I think this is one of the larger pieces of work in this project.' The person I was replying to sounds like they are on a bad team/project where people use their estimates to blame/finger point, and they are ascribing this to scrum as if the team wouldnt be doing this otherwise.

And in case you suggest that estimating without ascribing a time value is not meaningful, it is used to track how far you are through the project, and over time you refine what the finishing date will be given the emerging velocity.

> I might expect a dice roll to be 3.5, I'm not committing to the next roll being 3.5 - analysis should inform policy, in this case expectations informing stated commitments, but the two are not the same.

The analysis comes in discovering the velocity. The expectations evolve over time. But knowing your velocity is of limited use if you dont have an estimate of the overall size of the project.

> The difference is choosing to commit to an estimate you have high confidence in

This is the method for getting confidence in your estimate. You have an overall number of 'points' in the project and you learn how many points you can tackle on average every X weeks.

it is totally reasonable for stakeholders to want to track your progress through a project. If you have a good way of doing that then great, you should use that.

Scrum people believe that scrum is the simplest way of measuring that. But at some stage you have to estimate the constituent parts of the project in order to get an idea of its size, and for those estimates to be useful in tracking your progress you have to do it in advance.

I repeat however, if you dont need to do this then thats fantastic! Many of us do however, and some of us choose to use scrum to do that, and some of us have had a great deal of success with that.

(edit: I worry that this sounds condescending. I am just trying to keep the tone friendly)

(replying here because I guess we've reached the maximum depth)

I am here assuming that you want to be able to try to measure your progress through the project (as I mentioned, this is the only thing scrum does for you). Both of you seem to be suggesting (dont insult me if Im wrong) that this isnt the highest priority.

And no, velocity is to make the whole system self-adjusting. If I put 3 points against a story we use velocity to discover over time how long those 3 points take. This self-adjusts to incorporate for contingency.

If you disagree with this then we simply disagree on what velocity is about. It doesnt make us enemies, we dont need to get super pissed off at each other.

can we infer that he would like to give his estimates:

* while he is actually writing the code (so not up front)

* not in a group setting but as an individual, so either one person estimating the whole thing or each person giving different estimates

* (third point same as first, dont want to estimate up front)

* must incorporate what is often called 'contingency' (which is actually what the whole point of measuring velocity is for!)

* and the final point - he doesn't want to have to commit to it

how can you _not_ read this into it?

It sounds as though you objecting to being required to give any estimate at all.

if its being used to 'get velocity up' instead of measuring velocity then its not being done right.

I personally think estimating projects is one of the most difficult things about this industry. Especially if we're talking about delivering many calendar-months worth of effort for a team , unless its just a variant on some other project[s] the team is well experienced at

If you're objecting to people who treat scrum (or any project management tool) as a one-stop-shop that will cure all ills I agree with you, but nobody here is saying that.

If you are objecting to defining the scope as small tasks and measuring your progress through that over time, then continually re-evaluating this scope as requirements change, then I think you are not working in an environment that would benefit from this kind of tool.

Its just a pragmatic set of guidelines, and objecting to it with such ridiculous vitriol makes you sound as foolish as the people I think you're objecting to.

if pressure is ramping up and quality down the sprints arent serving their purpose.

One of the few defining characteristics of scrum is that the developers define how much they can achieve, and this estimation is improved over time. If this is not happening there is something else wrong with the culture and Scrum is being used as a scapegoat.

I agree, it is often not the best approach. But many situations demand a well defined approach to estimation and although the OP tried to preempt this, he didnt provide an alternative

oh and I have attended some of those expensive Scrum 1-week courses and saw the darker side of that community - it definitely has a cult following that give it a bad name, but I've been to similar conventions around design patterns, object-oriented and (to a lesser degree) functional programming so I think that the community problem is not particular to Scrum.

Scrum proponents (a label I would tentatively apply to myself) would tell you that 'you're doing it wrong' but unfortunately a point-by-point reply to this article would detract from the general problem here: Scrum is intended to be the straightest line towards measuring your real progress on a project, and not much else

If youre working on a project where it is important that you have as-accurate-as-is-realistic an idea of the size of the project, or more specifically your progress through that project, then I can't see how a methodology could be any simpler.

If having a good idea of the size of your project over time and your progress through that project are not very important from a management perspective, the Scrum artefacts will seem like, and will probably in fact be, needless overhead.

Scrum is not opinionated about the actual development methodology so claims about how it affects the code that is written are themselves a bad smell IMO.