2008/12/20 Eugene Alvin Villar sea...@gmail.com
Hi guys,
After seeing someone using Merkaartor (http://www.merkaartor.org/) to edit
in OSM, I decided to give it a try last night. Before this, I've been
exclusively using Potlatch. Potlatch is a pretty good application and is
definitely the best Flash application I've ever seen but I quickly ran into
one of its limitations while I was doing Eastwood City and Bonifacio High
Street. The limitation is that at the highest zoom level, you cannot place
nodes more accurately: the nodes snap to a 3-pixel grid. This 3-pixel grid
translates to a resolution of almost 3 feet at the latitude I'm working at.
This is more than good enough for roads, but not adequate for buildings.
(I'm kinda OC [obsessive-compulsive, slang in Philippine English] when
mapping the details of buildings, and this limitation prevented me from
making nice right angles of small idented corners of buildings. See this
view of Bonifacio High Street for example:
http://openstreetmap.org/?lat=14.550474lon=121.0513zoom=18layers=B000FTF)
I asked Richard, Potlatch's creator, about it and he acknowledged this
limitation (our conversation is at the OSM Wiki:
http://wiki.openstreetmap.org/index.php?title=User_talk:Richardoldid=161158#lat.2Flong_resolution_in_Potlatch
).
If you're using Potlatch, then Merkaartor gets some getting used to with
regards to its interface. The workflow is pretty much the same as in JOSM
(another OSM editor): you go to an area, download the data, edit at will,
then upload the changes. I like it because it doesn't have the
aforementioned 3-pixel limitation in, and in addition, it blows up the
Yahoo! map tiles if they're not available in a higher zoom level; Potlatch
just shows Yahoo!'s We're sorry, the data you have requested is
unavailable tiles. (I'm not sure if Merkaartor's behavior is allowed by
Yahoo!'s TOS).
I'll still continue to use Potlatch as a general editing tool since it's
pretty quick and I'm used to it. I'll just bring out Merkaartor if ever I
want some finely wrought detail. :-)
Merkaartor has improved each time I've used it and it's look pretty good
now, but, last time I used it it still seemed somewhat less responsive than
potlatch or JOSM and that was on a reasonably decent PC... On the one I'm on
right now, JOSM struggles so I don't dare try merkaartor...
JOSM also blows up the Yahoo imagery in the same way, not sure if it only
applies where there is higher level zoom data available or if the function
just can't cope with the boundaries between high quality imagery and low
quality imagery...
One of the other new features in JOSM that I'm not sure if Merkaartor has,
but, is quite useful for some buildings is the Orthogonalize tool, it only
works correctly if you have the projection setting set to Mercator instead
of the default EPSG:4326 but will warn you if that's not the case... It's an
advancement on the previous align in rectangle tool as it adjusts all
corners to 90 degrees, even on objects with more complex shapes (as long as
all corners are 90 degrees)... Something that could work well with the
buildings on Bonifacio High Street which are nice and orthoganal (though not
well at all with those of The Fort strip or Serendra)...
For multiple buildings that are the same shape JOSMs copy and paste
functionality and rotate functionality can also save time and effort, though
a flip vertically or horizontally function would be a useful addition for
'mirrored' buildings...
As you mentioned about Potlatch and it's snap to though, JOSM also has
snapping, yes, you can zoom in to entire screen = 1m to get around that,
but, it can be frustrating when JOSMs guide as to what will happen when you
create a node tells you it won't snap to another way, but, when you click 4
nearby ways all get pulled together, at least you can easily undo just that
last click, select the previous node and try again though and I seem to
recall there's some key stroke which you can use with the click to prevent
snapping, but, I forget...
d
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