[OSM-talk] Export too big
raybees at mac.com
Thu Jan 22 10:00:11 GMT 2009
On Jan 22, 2009, at 12:52 AM, Tom Hughes wrote:
> Russ Nelson wrote:
>> Earlier today, I tried an export almost 10K x 6K pixels, and got a
>> warning message saying that the export was too large. Perhaps that
>> message should contain a URL like http://wiki.openstreetmap.org/
>> which would either be a page on its own, or a redirect to some
>> page's subsection, as needed. I'm happy to write the text of that
>> page if somebody can change the export code for me.
> Can you explain a bit more about exactly what you tried to do and what
> the message you got was? Only the export tab doesn't give any such
> errors as far as I can see.
Hi! I'm Ray Bruman, the guy with the
original question, here to explain.
I am very surprised that the Export
I want is too big, because it would
be a very handy hiking map of a
fairly small district of San Francisco,
as you will see below.
60 megapixels may be a bit large
when you put it that way, but bear
with me and see if it's reasonable.
I think what I want to do shouldn't
be hard, but I can't figure out how
to do it, so I'll just try to state the
I want to print a simple black-white
line art map on 36" wide paper at
a service bureau.
I'm hoping and expecting that a
PNG file is fine, but if they require
a JPEG, so be it. The one I have
been to only understands JPEG,
so I may need to convert a file.
The region I want is a portrait-
oriented rectangle from downtown
San Francisco, centered on the
intersection of California and Sansome:
Width of rectangle 1867 meters
Height of rectangle 2467 meters
This translates to coordinates as
a rectangle bounded by:
The zoom level I want is the
maximum, sometimes called 18,
sometimes called 17 (??!!)
because some people begin
counting at zero instead of one,
for maximum level of detail.
This is the only zoom level that
actually has names for the
many tiny alleys, some only
a dozen meters long, that exist
in this historic section of old
I am willing to accept an image
that prints out to an approximate
size, which has to be enlarged or
reduced to eventually fit on 36"
wide paper. The important thing
is to achieve a clear B/W image.
This may require choosing a
zoom level that works well with the
pixel size of the printer, such as
300 dots per inch.
I'm willing to try and try again,
experimenting with different
settings. But I still haven't figured
out how to do it at all.
Here is an additional aspect that might
actually make the project easier.
Notice that the street grid of downtown
SF is oriented at a slight angle to true
If it is possible to rotate OSM's
selection box to align with the street
grid, I could select a smaller box,
because the one I specified was
designed to capture a region angled
This would also reduce the problem
of "aliasing" where a line is being
rendered at an angle to the grid of
pixels being generated by the software
and translated yet again to the dot
grid used by the printer.
I imagine that this issue comes up
many times for users. For example,
someone interested in a detail map
of the region south of Market Street
("south of the Slot" as old-timey San
Franciscans say) would want the
bounding box at a completely different
I would not be surprised if the
software lacks the capability to
rotate the selection box.
But, in case it can, I wanted to
mention this aspect of my project.
It might make the difference between
choosing one Zoom level or another
that is much closer to the scale
needed to place the region on
paper that is 36 inches wide.
Of course, a clear print-out that
is smaller can be physically cut,
rotated, and re-scanned to make
the eventual map 36 inches wide.
I expect to have to do this anyway
to fine-adjust the map's final scale.
If any of you succeeds in exporting
a file for the region I want, please
make a note of the file size and
let me know. If it is under 650 MB
so it will fit on a CDR I would
greatly appreciate your burning
it on a CD and giving me a call.
I would gladly buy you a beverage
of your choice at the soonest
Home (510) 549-1509 Cell (510) 295-5537
raybees at mac.com
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