Charts

[Leo12305]

Hi Sinbad7
at the moment there is not program in our homepage you are right. We change the homepageto the start of bootsfair in Duesseldorf. Today can send you some converted chart of baltic sea. you will find it in your e-mailbox.
Leo

[sinbad7]

Leo..

Thank you Leo but I don't need the charts but I need your program or explanation as to how you determin the scale (i.e. 1:200.000) of a screen captured bitmap from OpenSeaMap.

Regards
Tore

[Leo12305]

Originally Posted by sinbad7

Leo..

Thank you Leo but I don't need the charts but I need your program or explanation as to how you determin the scale (i.e. 1:200.000) of a screen captured bitmap from OpenSeaMap.

Regards
Tore

Ok Sinbad7

the program is only running if you have all tiles from the used aeria. For this I have own server runing.

I will give the calculations for the zoomlevels.
# calcualate meter per pixel
my $lfm = 40024/360*1000*($N-$S)/$width ;
with in px

each has has 256 px if you know the Number of tiles you can calculate is easy.
leo

[sinbad7]

Leo..

I take it '$lfm' = scale (as in 1:200.000)
Are '$N and $S' number of tiles and pixels?

Otherwise I have calculated the scales of some of your zoom levels as follows:
Zoom 9 - 10 nm - scale 729.133
Zoom 10 - 5 nm - scale 364.565
Zoom 11 - 2 nm - scale 145.827
Zoom 12 - 1 nm - scale 72.914

Above this zoom level,all are shown as 1 nm???
Zoom levels below 9 are mostly un-readable being blocked by your information logo.

As you see from the attached my Opera browser also displays the tiles.

[Leo12305]

Originally Posted by sinbad7

Leo..

I take it '$lfm' = scale (as in 1:200.000)
Are '$N and $S' number of tiles and pixels?

Otherwise I have calculated the scales of some of your zoom levels as follows:
Zoom 9 - 10 nm - scale 729.133
Zoom 10 - 5 nm - scale 364.565
Zoom 11 - 2 nm - scale 145.827
Zoom 12 - 1 nm - scale 72.914

Above this zoom level,all are shown as 1 nm???
Zoom levels below 9 are mostly un-readable being blocked by your information logo.

As you see from the attached my Opera browser also displays the tiles.

lfm = meter per pixel

N -S are degrees in decimal

width are the pixel from left to right Side of the use aeria
I send you a Chart from Baltic Sea this a Skale 1:353400

leo

[sinbad7]

Leo.. This is a bit like pulling teeth...

What are the variables $N and $S ? Max and min latitude of the map?
So, when we have the result of $lfm= meters per pixel,how do we calculate the scale?

Sorry, but we'll get there in the end...

[Leo12305]

Originally Posted by sinbad7

Leo.. This is a bit like pulling teeth...

What are the variables $N and $S ? Max and min latitude of the map?
So, when we have the result of $lfm= meters per pixel,how do we calculate the scale?

Sorry, but we'll get there in the end...

What is your problem all our tiles has 72 dpi.

if you know this, use this

mass = lfm * 72/2.54*1000;

mass is your scale

If you have an other dpi use this value instet of 72

leo

[sinbad7]

leo...

Thanks for your patience.. I repeat total procedure to find SCALE (mass) of a map:

$mass=((40024/360*1000*($N-$S)/$width))*(72/2.54*1000)

$lfm = 40024/360*1000*($N-$S)/$width (meter per pixel)
Tile size 72 dpi. Tile width=256 pixels.
Variable $N top latitude in dec.deg.
Variable $S bottom latitude in dec.deg.
$width=tile numbers in chart * 256 (full chart width)

It will be fun to experiment...

[sinbad7]

leo..

I used your chart SCALE formula on a new map of the German North Sea but it does not make sense. Based on a 10nm to the inch,the scale should be 1:729133 but your formula came out at 1:6243433

The calculations were made as follows:
$lfm = 40024/360*1000*(55.59909-53.06328)/1280 (5 tiles x 256)= 220.25445
(72/2.54*1000)= 28346.456
Finally 220.25445*28346.456= 6243433

What went wrong?

You can download the GermanNortSea.kap here to check:

[Leo12305]

Originally Posted by sinbad7

leo..

I used your chart SCALE formula on a new map of the German North Sea but it does not make sense. Based on a 10nm to the inch,the scale should be 1:729133 but your formula came out at 1:6243433

The calculations were made as follows:
$lfm = 40024/360*1000*(55.59909-53.06328)/1280 (5 tiles x 256)= 220.25445
(72/2.54*1000)= 28346.456
Finally 220.25445*28346.456= 6243433

What went wrong?

You can download the GermanNortSea.kap here to check:

Hi Sindbad7

I make a new chart from the same areal in zoom level 10

I send it to your e-mail adress. my calculation is 1.1.592.555 for this areal

These calculation is not constructed from me, I find in a other program.

greetings leo

[sinbad7]

Hi all..

As there does not seem to be much interest in the development of Open Source charting facilities,I will belay my sails until more favourable winds will blow.

Thanks to those who gave support..

[idpnd]

The question is really how this could be implemented as an overlay..

[sinbad7]

idpnd...

Whilst it is possible to do privately,I don't think the overlay method is a viable method for the users of OpenCPN. A totally Open Source map system is required as mentioned in one of my previous postings:

Interesting news from the Norwegian Coast Guard which has adapted OpenSeaMap.

The Norwegian Coast Guard is now offering a free charting service for Norway.
The new development is that they are using OpenSeaMap as a base,with choice of up to date ECDIS compatible nautical charts for the entire coast of Norway. Presently only available via internet.

All the nautical charts are collected directly from 'Sjøkartverket' ,the coast guard's charting service. The maps are collected as WMS (Web Map Service) Each time the user pans or zooms the chart,a call is made to the Sjøkartverkets WMS server,making sure you reveive the very latest chart information. If OpenCPN could be made WMS compatible, it would in theory be possible to collect the charting data direct from Sjøkartverket.

About the WMS service:

Perhaps a similar model could be adapted for use with other free charting services such as USA and Brazil.

As the data is presently only available over the internet,I suggested that perhaps arrangements could be made to download particular chart areas prior to each planned trip which could later be updated or deleted as required. This would avoid having to download the entire and huge database.

I have suggested that we could all benefit from a discussion to find a solution to offer a total FREE navigation package to the boating fraternity.

Until someone with the skills and motivation to check out the possibility to incorporate WMS or similar into OpenCPN we are not going to make significant headway.

[idpnd]

That's what I mean, we will have to wait until someone comes along and implements a technical solution

[sinbad7]

I agree and challenge:

Until someone with the skills and motivation to check out the possibility to incorporate WMS or similar into OpenCPN we are not going to make significant headway.