NOTICE: help.openstreetmap.org is no longer in use from 1st March 2024. Please use the OpenStreetMap Community Forum

I've exported the map region to jpg in 1:1000000, the resolution, shown to me was 2019 x 1866; area сoordinates was so: N 56.9583; E 40.3617; S 54.3107; W 35.2828 (it is the Moscow oblast) so my question is: what should be the DPI factor (in photoshop for example) to print that image in 1:1000000 ???? because DPI factor by default is 72 and printed picture doesn't match to the scale 1:1000000. The same problem appeared in archicad, when I made import of the drawing (I tried it with JPG and Pdf format)the scale was also wrong. I'm working in metric system and I thought the problem is in that? but I tried different convertation and nothing helped??

I tryed to describe my question in link below

http://help.openstreetmap.org/upfiles/scale_factor.jpg

asked 12 Apr '12, 23:24

sergpomelov's gravatar image

sergpomelov
26114
accept rate: 0%

edited 15 Apr '12, 14:26


That's what I did:

  1. Get an image of a known distance, at a given scale (say: 100m at 1:5000)
  2. Get map size it should have: 100m / 5000 = 0.02m = 2cm
  3. Measure that distance in pixels of obtained image: 100px so far surprise!
  4. Calculate: 100px / 2cm = 50 px/cm. That's the resolution
  5. Want it in inches? 50px/cm * 2,54cm/in = 127px/in

As this measures are quite inaccurate, maybe you should try with different distances and map scales. I made it twice, and the second time I got 112.27 px/in, so I think it should go around 120dpi.

Note: dpi is "dots per inch", and, as screen 'dots' are pixels, I used dpi and pixels/inch as the same unit.

permanent link

answered 13 Apr '12, 16:03

samel's gravatar image

samel
11112
accept rate: 0%

I'm not so small, dady ))) But thanks a lot, Now i'm doing that with latitudinal way' I tape direct nombers in zone coordinates (not N 56.9583, but 57 not S 54.3107, but 54 not... and so on) the distance of 1_o of meredian is approx 111 km and it is quite all right for me.. for now... but I think that OSM steel needs to improve some resolution and unit parametr in export menu (for not to spand a time for that)

(14 Apr '12, 01:41) sergpomelov
permanent link

answered 14 Apr '12, 21:35

sergpomelov's gravatar image

sergpomelov
26114
accept rate: 0%

may be that coment is not for OSM system, but for supporting products... SO, using Maperitive (now I began to work with vector :) )I tried to export OSM data to illustrator and Inkscape at the same time )) so... for my great wondering, after export that data to dxf format I found that in Archicad they came with different size... after a fiew hours of interest I understood some primitive thing ! attention ! INKSCAPE EXPORT DATA IN 90 DPI AND ILLUSTRATOR EXPORT IT IN 72 DPI ! attention ! at the same time the resolution of my monitor is http://members.ping.de/~sven/dpi.html see next coment

(15 Apr '12, 11:42) sergpomelov

1366 X 768 with 15.6" diagonal... (100.45 PPI/points per inch/)thats why imported data was a bit bigger. So I scale it down to my real monitor size. In my case it was 381,56mm to 341,86 (that is the exported box size not the monitor / my monitor size is 34.54cm × 19.42cm //see link, in previous coment by the way I found it in Maperitives help///and I exported it from INKSCAPE /90 DPI//PPI for monitor///)

(15 Apr '12, 11:55) sergpomelov

And as for OSM... Actualy I wouldn`t ever do all that if I onley had real 100mm leng virtual line (exportable to PDF) in the left down corner, close to the scale line (also exportable). But now I know everything about map scaling. Thanks for your attention.

(15 Apr '12, 12:13) sergpomelov

From that wiki page you get these basic formulas:

resolution = 156543.034 meters/pixel * cos(latitude) / (2 ^ zoomlevel)

The resolution means how many meters per pixel you get.

scale = 1 : (dpi * 39.37 in/m * resolution)

The scale means, how many cm in reality is 1 cm on the paper (or on the screen).

So if you have a screen with 96 dpi, you get that one pixel is 1.1943 meters. And you get a scale of 1 : 4 231 which means that 1 cm on your screen is 42.3 m in reality.

If you have a printer which prints 300 dpi … (now do the calculations yourself).

I hope this helps you getting the right size of your image.

permanent link

answered 14 Feb '14, 12:00

erik's gravatar image

erik
558152234
accept rate: 9%

-2

The exported image is using mercator projection. This projection does not preserve scale. The exported image is scale 1:1000000 if you export an area near the equator, but this becomes a bigger scale the longer north or south you get. When you are comparing this map with a map in a projection that preserves scale better like utm you will see that they do not match. You will also notice other differences in the projections.

permanent link

answered 13 Apr '12, 01:28

Gnonthgol's gravatar image

Gnonthgol ♦
13.8k16103198
accept rate: 16%

1

I dont think that answers the question. The problem is that the export tab lets you specify a 1:X scale, but that number is meaningless without an associated DPI (since the export is in pixels, it doesn't make sense to say "map is 1/Xth the size of reality" if you do not know the physical size of your printed/displayed pixel). The export tab should either say what DPI is used, or allow to set the DPI.

Concerning projection deformations: 1) zoom in sufficiently 2) let the export tab adjust the scale from the latitude.

(13 Apr '12, 10:53) Vincent de P... ♦

M ) I see, but the scale is smaller??

(13 Apr '12, 11:11) sergpomelov

zoom distanse does not matter, picture details depends on a scale factor you tape... as I understand... (and you always have maximum limit of a scale factor) and by the way, small scale line in low left corner is correct I checked it

(13 Apr '12, 12:55) sergpomelov

made the way you toled me using latitude !!! greate !!! I think somehow OSM arrange that problem later ) thanks a lof for hi light decision (hard to find it sometimes)

(13 Apr '12, 14:22) sergpomelov

Follow this question

By Email:

Once you sign in you will be able to subscribe for any updates here

By RSS:

Answers

Answers and Comments

Markdown Basics

  • *italic* or _italic_
  • **bold** or __bold__
  • link:[text](http://url.com/ "title")
  • image?![alt text](/path/img.jpg "title")
  • numbered list: 1. Foo 2. Bar
  • to add a line break simply add two spaces to where you would like the new line to be.
  • basic HTML tags are also supported

Question tags:

×23

question asked: 12 Apr '12, 23:24

question was seen: 14,205 times

last updated: 14 Feb '14, 12:00

NOTICE: help.openstreetmap.org is no longer in use from 1st March 2024. Please use the OpenStreetMap Community Forum