Prevent combining ways where relations are not loaded

[mdk]

I got a huge problem when I merge two ways where JOSM din not download the ralations. This cause that some other relations has deleted ways as members.

This can happen if you download the members of a relation and combine two ways which are outside the boundig box (which means that their relations are not loadad).

Here is an step by step example:

1. start JOSM
2. File->download object...relation 1556696
3. combine (c) two ways at the lower left beginning of the primary highway (110009332 and 88954933)
4. download a boundig box including both ways
5. There is now an error "The was 1 conflict detected"
6. look at relation 1556773 (residetial with 17 members) which still contains the way 110009332 with 0 nodes!

[skyper]

It is always on user's risk to edit with incomplete data. There for you have to download all references of a way before deleting or splitting.

I do not see any problem within JOSM and the conflict resulting on your edits is shown.

Only thing I can think of is a check weather you are editing on a complete area downloaded as bounding box or on an incomplete area with only some objects downloaded.

[mdk]

Because combining ways is an implicit delete, why can't you show the same warning as on try to deleting a way, which is in an incomplete area? Just do the delete check on the ways which are choosen for deleting.

A general thing about usability in this case:
How dose a user should know when he could do such an operation without beeing affraid, to corrupt the data?
When I came into this problem, I saw two ways which belongs to some relations, both ways belongs to the same relations and had the same tags, so I decide to combine them. But I can't see, that one of the ways is also a member of a relation which is not already loaded.

So you mean, the user must know the internal algorithem when JOSM load missing relations of an element and when not? How dose a user should know when all relations are loaded?

I'm not a newbe in using JOSM, but I still have the problem, especially when I (must) work in areas where nearly eveything is a MP!

[simon04]

It's quite easy to run in such problems:

1. Download a relation via Download objects, e.g., the boundary 943282.
2. Note that the members are not part of any other relation, but in fact they are (e.g., download the way 60665540 to see the second relation).

[simon04]

Replying to simon04:

It's quite easy to run in such problems:

1. Download a relation via Download objects, e.g., the boundary 943282.
2. Note that the members are not part of any other relation, but in fact they are (e.g., download the way 60665540 to see the second relation).

This occurred due to not using "Download referrers"

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To display this warning, JOSM must be aware of potentially existing relations. I don't think that JOSM currently knows. To add this, JOSM would need to keep a history of how any object was added to the dataset. I don't think this is reasonable.

Instead, I suggest a simpler solution: Let's remove the "Download referrers" checkbox from the "Download object" dialog for the non-expert mode. What do you think?

[mdk]

If you want to remove "Download referrers" in non-expert mode, then only, if "Download referrers" is set to true. But that will not solve the problem, because there are a lot of functions which load data without loading the referrers.

As far as I know, there is a function in JOSM to estimate, if all referrers to an object are loaded.
for a node: check if the node is in one of the bounding boxes the user has downloaded.
for a way: check if any of the nodes is compleatly loaded (see above)
for a relation: check if any member is compleatly loaded (see above)
Simply warn if an object is deleted, which not pass this check.

An other possibility is trying to download refferers before merging object (at lest for the object which will be deleted)

In general it would be possible to add a flag to any object, which will be set to true if explicitly all refferers has been loaded (which may be none). This flag will be set on downloading a bbox (see above) or if "Download referrers" is used. This way JOSM can easily warn if an object is about to be deleted and there may be unloaded referrers. (For memory efficeny you can use an int for 32 flags with getters and setters for modifying the bits)