[Talk-de] Potlatch (Re: Multi-User "randale" ( s?dlich Reutlingen/T?bingen ))

[Richard Fairhurst]

Apologies, as a non-German speaker I can only half-follow this  
discussion through Google Translate, and I realise it's very rude to  
post in English on a German-speaking list. I thought it would  
nonetheless be valuable to follow up two points in particular, hope  
you don't mind.


Andre Rechelt wrote:

> Ich frage mich ganz einfach, was sich die Entwickler von Potlach  
> heraus nehmen, um im Gegensatz zu ALLEN ANDEREN direkt in der  
> Datenbank herumzupfuschen und nicht den Weg ?ber die API gehen.

Potlatch does not have, as you have put it elsewhere, a "direct  
tunnel to the data". This just isn't true.

Potlatch (the application) uses an API, just as JOSM does, which  
sanitises requests, requires authentication, etc. There are three  
significant differences between that part of the API used by  
Potlatch, and that part of the API used by JOSM etc.

- Potlatch uses a different encoding (AMF rather than XML). This is  
simply for the sake of efficiency: older (Actionscript 1)/free  
(Gnash) Flash players work much better with AMF than with XML.  
Encoding, of course, makes no difference to the data.

- Some of Potlatch's calls are constructed differently. Some of this  
is for historical reasons - you might be too new to realise this, but  
in earlier versions of the API, we had three object types: ways  
(comprising a chain of segments), segments (connecting two nodes),  
and nodes. Potlatch (which has always had broadly the same UI)  
abstracted segments away from the user. Therefore the API functions  
provided _at_the_time_ were not particularly suitable.

Since then, the rest of the API has in fact moved closer to Potlatch  
through the abolition of segments (Frederik and Gabriel's work,  
thanks :) ). I believe that there is some will to provide the rest of  
the API with the remaining Potlatch-only functionality (in  
particular, a PUT /way/<id>/full method).

Bear in mind too that, at present, the design of the main API calls  
are better suited to an offline editor (like JOSM) than an online one  
(like Potlatch). In particular, the /map call pulls down the entire  
contents of the bounding box every single time. This would mean that,  
every time the user panned the map in Potlatch, all the ways and  
nodes would be sent again - even if the user had only panned left by  
10% of the screen area. Instead, Potlatch takes an approach which  
does not require already-loaded ways to be resent, with significant  
benefits for bandwidth and server load.

- A significant proportion of the code in amf_controller.rb uses SQL  
rather than Rails objects. Except in some cases where SQL provides a  
significant speed advantage, this is generally accepted as a defect.  
It's only the case because I don't speak Rails. If you want to do  
something constructive, fixing this would be the single best place to  
start, and would be enormously welcomed by many people including  
myself. Please take it forward to the dev list if so - you'll find  
lots of people willing to help you!



While I'm here I might as well say something about the lack of a Save  
button.

I'm not violently against the concept: I think "unconvinced" is  
perhaps the best way to describe my opinion.

There are two big issues with it. One is that for edit sessions  
lasting more than a couple of seconds, there has to be conflict  
management. If you're a JOSM user, then you are de facto a  clued-up,  
computer-savvy type, so conflict management doesn't worry you. But if  
you are a newbie - maybe even a schoolkid - trying just to edit your  
local area, then being presented with "The following conflicts were  
detected. Accept/Resolve/Revert?" will just utterly confuse you, and  
you'll click the wrong thing and cause more errors. Or maybe just  
close Potlatch and never return to OSM.

The second is that, in JOSM, your "canvas" is usually quite small -  
i.e. you have downloaded a particular area and are working on that  
exclusively. In Potlatch, because you can pan around an infinite map,  
your canvas may be much bigger. You may have traced a 600km cycle  
route (I know, I've done that! :) ) in one session. Yet you can't  
zoom out to see the whole thing, because requesting a 600km bounding  
box would break both the server and the browser. So you would be  
clicking "Save" to upload changes that you can't actually see or  
review, and that - in my opinion - defeats the point of it.

But actually they're not my biggest problem with the idea.

What worries me most, because I've seen it before, is that people are  
seizing on the first thing they don't like, and thinking that's the  
reason why there are bad edits. People used to criticise Potlatch for  
causing bad edits because there was no 'revert' feature, so I added a  
revert feature (the H key). Then they criticised Potlatch for causing  
bad edits because there was no 'test' mode, so I added a test mode.  
Then they criticised Potlatch because there was no 'splash screen'  
explaining things, so I added a splash screen. Now they criticise  
Potlatch because there's no compulsory 'save' button.

But if I added a compulsory save button tomorrow, it wouldn't stop  
the bad edits. The bad edits are principally because these guys are  
newbies. Newbies make mistakes. (Experienced users don't make  
mistakes with Potlatch just because it has no Save button.)

And in a week's time, someone would be saying "Potlatch must be  
banned unless it has a pony" (or something) and there'd be a lot of  
postings saying "yes, the reason there are all these bad edits is  
BECAUSE POTLATCH HAS NO PONY". And so, a few weeks later, Potlatch  
would get a pony, which would make it even harder to use (ponies are  
quite stubborn, you know) and require newbies to learn even more, and  
then someone would decide on another "reason" for the bad edits...  
and so on.

That's not to say that Potlatch can't be improved. Of course it can,  
a lot. One simple easy-to-fix thing which I'm planning to change  
soon, and which I think would make an enormous difference, is  
actually to have a very prominent "uploading..." display when a way  
is being uploaded. This would make it pretty obvious the first time  
that you changed something that it was writing to the map. You would  
make one bad edit, maximum. (In general, making what's happening  
"transparent" and obvious is a good thing, and Potlatch doesn't  
follow that principle enough at the moment.)

Another thing is localisation, so that the advice at the start - "If  
you click 'Start', you'll be editing the main map directly" - shows  
up in German, too. Lots of you have offered help with that, which is  
great - thank you all; I hope to have some more news on that really  
soon.

mfg :)
Richard
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