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Thamor

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Donnerstag, 29. Oktober 2009, 21:49

DereGlobus Maps

In the past we have thought about a browser version of DereGlobe using the google earth browser plugin, see this thread. There are several problems with de plugin: default compression of map files which is ugly with png, structural deformed balloon content and last but not least the installation of the plugin itself.

Wouldn't it be nice to use google maps instead of the google earth plugin? No installation, quick loading, access for linux computers - and a flat world! :D
And the killer argument: google maps is an online collaboration tool! You can edit the map (placemarks, polygons, ...) in your browser together with other users!

The reason why the thread title is not DereGlobus:
  • the google maps application should only contain the continent aventuria not the hole globe
  • it's flat, so it is only called "maps"
  • it's in englisch because it is a jount venture with Italy! :)


And now the big question: Can we load our kml files in google maps? :?:
And if yes: Can wie import them back to DereGlobe?

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Samstag, 31. Oktober 2009, 00:17

Re: AventuriaMaps

Just a small visit to google maps to plan my journey in holiday ... here the [url=http://maps.google.de/maps/ms?ie=UTF8&hl=de&msa=0&msid=100488044530702774571.000476f010e0ffd38a146&ll=32.630123,9.09668&spn=7.370734,14.27124&z=7]result[/url]! :D
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Thamor

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Samstag, 31. Oktober 2009, 00:20

Re: AventuriaMaps

And the way backward. (See kml attached)
Casualties: the CSS style in the balloon.

Incredible. Awsome. Revolutionary. :D
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Samstag, 31. Oktober 2009, 20:22

Re: AventuriaMaps

Zitat von »"Thamor"«

And now the big question: Can we load our kml files in google maps? :?:
And if yes: Can wie import them back to DereGlobe?

Zitat von »"Thamor"«

Just a small visit to google maps to plan my journey in holiday ... here the [url=http://maps.google.de/maps/ms?ie=UTF8&hl=de&msa=0&msid=100488044530702774571.000476f010e0ffd38a146&ll=32.630123,9.09668&spn=7.370734,14.27124&z=7]result[/url]! :D

Zitat von »"Thamor"«

And the way backward. (See kml attached)
Casualties: the CSS style in the balloon.

Incredible. Awsome. Revolutionary. :D



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Viridovix

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Samstag, 31. Oktober 2009, 22:44

Re: AventuriaMaps

LOL

Of course you can... and I can too ;-)

Just two code lines:

Quellcode

1
2
   var kml = new GGeoXml("http://maps.usnb.it/dati/daniel.kml");
   map.addOverlay(kml)


Take a look here: http://maps.usnb.it/kml.html (zoom out to see where the icons are placed)

As espected, the cities result misplaced. This is due to the fact that I used a Euclidean projection (i.e. flat map) and, probably, to my assumption about the position of Lat 0°, Lng 0° point. For my information, the only stated fact is that the Lng 0° meridian pass through Vinsalt... moreover, we adopted the double size option for Aventuria...

And of course the InfoWindow CSS is lost. This is due to the fact that all the kml overlay is managed directly by Google Maps API... but I will take a look about this problem.

Another problem I noticed is that some info window link are wrong: the maps.usnb.it is preponed to the absolute link to Wiki-Aventurika...

I'm writing a small english page about "How I did it" with all the problems encountered in AventuriaMap making. I will link it as soon as possible.

V.

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Donnerstag, 5. November 2009, 00:43

Re: AventuriaMaps

thread up.

I wrote some words about Google Maps here:

http://www.usnb.it/wiki/index.php?title=…AventuriaMap/en

Take a look about the considerations I did about placing Aventuria on Dere... this can explain the misplaced cities when I include your KML in my Google Map.

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Viridovix

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Samstag, 14. November 2009, 01:56

Re: AventuriaMaps

I needed to place the course of "Die Fahrt der Korisande", thus I started from the map available in the adventure book and repaint it to obtain a new map based on the same style of Kartenset.

Take a look here (follow the red line ;-) )

http://maps.usnb.it/index.html?avventura…lla%20Korisande

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Thamor

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Dienstag, 17. November 2009, 14:10

Re: AventuriaMaps

Zitat

And of course the InfoWindow CSS is lost. This is due to the fact that all the kml overlay is managed directly by Google Maps API... but I will take a look about this problem.
Okaaay, by the API - sounds complicated... :roll:

Zitat

Another problem I noticed is that some info window link are wrong: the maps.usnb.it is preponed to the absolute link to Wiki-Aventurika...
Äh, I think this problem is due to the raw test-data of Weißtrobrien I've used.

@Korisande:
Wow, your photoshop-work of the islands is quite nice! If we would not already have fine maps from Corabis... ;)
By the way: The Korisande-Adventure is of interest again, because of the planed Uthuria campain!

@Uno Sguardo nel Buio:AventuriaMap/en

Zitat

(in the future) he will be able to position the cities, the most important places and adventures routes. [...]
You can link the page focusing on a town or city [...] I should realize an interface to allow authorized users from inserting objects on the map
Sounds great! :D

Zitat

The project completion, at present, required some basic operations, which we shall see in detail, including:
  1. scanning and acquisition of original maps
  2. combining all maps
  3. defining the tiles
  4. writing the javascript code to implement the map with Google Map API
  5. implementing all the necessary server components
1 to 3 I have also done for DereGlobus, but 4 to 5 sounds like a lot of know how.

Zitat

This observation has implicated the first two interventions on the javascript code: the creation of a custom Scale Control, which does not take into account the latitude, but the level of zoom only and a custom Projection that implement custom Euclidean projections.

Another set of interventions have been about the customization of the interface. Here we adopted a library (ExtInfoWindow) that allow customization of default Google Info Window and then we made the images to compose the custom marker.
Oh, I don't understand anything. Well I'm not a programmer, so I think there is no chance for me to understand.

Zitat

The georeferential data are stored in a MySQL database [...] Another PHP script provides the XML file with all the data requested by the client.
In DereGlobus we do not use a database at this time - but there are plans! I see: In this direction you are one a higher level than DereGlobus.

Zitat

Placing Aventuria:
Whilst we could, in effect, put the map, or their tiles, assuming any starting meridian/equator reference, we preferred to place the map accordingly to some information provided by official sources: [...] Now, to correctly position the map the geographical coordinates of at least two points are required, or alternatively the coordinates of a point and the distance in kilometers between two points. In fact, with a single point you can get the positioning of the map, but not the scale level.
Ah, yes... at the beginning of the project we've spent a lot of time to evaluate the position of Aventuria - together with Thomas Römer and Stefan Küppers. Here the results: Traktat zur Gestalt Deres | Video.

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Viridovix

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Mittwoch, 13. Januar 2010, 17:15

Re: AventuriaMaps

Well, I made just few test to evaluate the best evolution of a multiversion AventuriaMap.

I created a PHP tile server to manage different version of the tile set, and this is the result (just a test, of course):

http://maps.usnb.it/gt.html

There is a small checkbox just above the combo for town selection. If this control is checked, a different version of tile set is enabled. In this test case only one tile at zoom level five is added for this second version. Thus, the tile server is invoked as usual with zoom level, x and y tile coordinate and the version. If a tile with such requisites is available, it is served; in case of missing tile, the default one is served.

For test, check the box and move the map to see the top left corner: a sea tile with "Checl box test" is shown. Uncheck the text box and move around the map, to force the tile reload (the tile to be reloaded must be outside the viewport) and you can see the default tile without text.

This approach can be used if we have different tile versions (i.e. custom map produced by the community) even if just one tile of the entire map.

Moreover, I created another different tile server able to manage the QuadTree structure for tile file naming. I tested this with Dereglobus tile set:

http://maps.usnb.it/dereglobus.html

(warning, this test case can be really slow because all the file are placed in a single directory)

V.

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Thamor

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Donnerstag, 14. Januar 2010, 10:52

Re: AventuriaMaps

Absolutly great! :D

Zitat

(warning, this test case can be really slow because all the file are placed in a single directory)
Can you explain me, why this is bad in case of performance? Because also in DereGlobus all data (KML and JPG) is in a single directory.

Well, the next step is to calibrating the map to the same coordinates for aventuria as it has in DereGlobus, right? This are the coordinates for the overall map: :D

Quellcode

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3
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		<north>44.68523182173993</north>
		<south>13.83211470255367</south>
		<east>13.82951187257615</east>
		<west>-8.928795211729799</west>

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Viridovix

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Donnerstag, 14. Januar 2010, 18:39

Re: AventuriaMaps

Zitat von »"Thamor"«

Absolutly great! :D

Zitat

(warning, this test case can be really slow because all the file are placed in a single directory)
Can you explain me, why this is bad in case of performance? Because also in DereGlobus all data (KML and JPG) is in a single directory.


Basically because the file system access performances can be influenced by the number of files, if the number of file is huge and they are placed in a single directory. A good practice is to create a directory tree that can be easily computed. As example, in mediawiki file system the images are organized in a directory tree and all the path for a specified file is related to the hashcode of the filename.

In a quadcode filename pattern (as you choiced for the Dereglobus tile set), probably the best choice is to have a directory tree based on zoom level character... (i.e., in your case, 6 directories called A,B,C,D,E,F, each one with 4 subdirs called 1,2,3,4 and so on...

Zitat


Well, the next step is to calibrating the map to the same coordinates for aventuria as it has in DereGlobus, right? This are the coordinates for the overall map: :D

Quellcode

1
2
3
4
		<north>44.68523182173993</north>
		<south>13.83211470255367</south>
		<east>13.82951187257615</east>
		<west>-8.928795211729799</west>


Yesss.... I will check with such coordinates in a few days.

EDIT: BTW, all the coordinates are for the map edge?

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Montag, 15. Februar 2010, 11:41

Aventuria Maps - Joint Venture between USNB and DG

Regarding the tech question, I'm sorry for my late, but I had some trouble at work (too much things to do, and so few time...), but at the end, I found the problem in coordinates misalignement.

In Google Map there are two ways to place your own custom tile set on a map:

1. implementing a new tile overlays
2. implementing a new custom map type

Each method has pros and cons.

By tile overlays method you can place a given tile everywhere on the map, providing boundary coordinates, but in Google Map these tiles are placed over the google map tiles: this approach is useful if you need to place some information over existing map (for instance, traffic information changing the street colour). See this example:

<a class="postlink" href="http://code.google.com/intl/it/apis/maps/documentation/examples/tileoverlay-simple.html">http://code.google.com/intl/it/apis/map ... imple.html</a> (transparent tiles with only red cross are placed over the map tiles)

And this is a traffic tile from Google:

[attachment=0]<!-- ia0 -->traffic.png<!-- ia0 -->[/attachment]

Of course, you can set your tile provider in order to send an opaque tile to hide the google tiles, or set the GCopyright boundary appropriately, but this could be not enough if you have a tile set that not covers a rectangle area and can be poor in performance (in any case, two tiles layer are sent to the client).

In usnb map I adopted the more powerful custom map type approach. This method allows me to create a really new custom layer, it is possible to create a new paradigm (i.e. changing coordinates system, defining several tyle overlay over the basic custom map and so on). The problem with this method is that you cannot place your tiles defining the bounary coordinates!

You must create your tiles in a way that they can be mapped exactly on the default map tile. As example, at level zero, your single tile must have boundary coordinates of -180 and 180 for longitude and (more or less) +85 and -85 for the latitude.

When you zoom in (level 1) you have 4 tiles that must cover the same area, so, they are:

tile (0,0): long boundaries -180 and 0, lat boundaries 85 and 0

tile (1,0): long boundaries 0 and 180, lat boundaries 85 and 0

tile (0,1): long boundaries -180 and 0, lat boundaries 0 and -85

tile (1,1): long boundaries 0 and 180, lat boundaries 0 and -85

So, for instance, you cannot place at level 1 a tile with boundaries -90 and 90 in long and 0 and -85 in lat.

Using custom map type approach, the tile border coordinates are automatically computed by the zoom level.

Thus, your tile AvA (that is more or less at zoom level 5, I think):

<LatLonBox>
<north>44.6852318217399</north>
<south>34.4008594486778</south>
<east>2.4503583304232</east>
<west>-8.9287952117298</west>
</LatLonBox>

has not a corresponding tile on the default map tile set. The closest is probably the tile 15,12 (03311 in QuadTree) as you can see in this picture.

[attachment=1]<!-- ia1 -->tile03311.png<!-- ia1 -->[/attachment]

There are differences in both lat (4 degrees) and long (2 degrees), and these are the differences I experienced placing your AvA tile as 03311 on usnb map.

I don't know much about google earth, but probably its custom tile settings works like custom tile layer in Google Map.

I made a C# program able to re-create the tiles accordingly to the default tile scheme of Google Map, I'll try on your tiles to make everything works in Google Map Custom Map too... but this means that it is not possible to use the same tile set for Google Earth and Google Map.

To solve the situation I think there are several approaches:

1. using the tile overlays approach in Google Map (but I don't like this, because this means poor performance and difficulties adding another overlays if needed);
2. re-cut the official tile set in order to map the tiles as per official Google tile set and adopt the custom map type approach (I prefer this approach, but I think you must do some tests on Google Earth too;
3. mmm.... at the moment, I haven't a third option, but I'm working on it.

Tschuss

Giuseppe
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Thamor

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Montag, 15. Februar 2010, 15:46

Re: Aventuria Maps - Joint Venture between USNB and DG

Zitat

In Google Map there are two ways to place your own custom tile set on a map:
1. implementing a new tile overlays
2. implementing a new custom map type
Allright, I understand. DereGlobus on Google Earth is made with Method 1: Tile overlays on top of the Earth map.

Zitat

Of course, you can set your tile provider in order to send an opaque tile to hide the google tiles, or set the GCopyright boundary appropriately, but this could be not enough if you have a tile set that not covers a rectangle area and can be poor in performance (in any case, two tiles layer are sent to the client).
Ok, I get the cons of using tile overlays, especially in terms of performance...

Zitat

In usnb map I adopted the more powerful custom map type approach. This method allows me to create a really new custom layer, it is possible to create a new paradigm (i.e. changing coordinates system, defining several tyle overlay over the basic custom map and so on). The problem with this method is that you cannot place your tiles defining the bounary coordinates!
Oh, that's bad... Perhaps it's possible for me, to cut the aventuria map in an other manner...

Zitat

You must create your tiles in a way that they can be mapped exactly on the default map tile. As example, at level zero, your single tile must have boundary coordinates of -180 and 180 for longitude and (more or less) +85 and -85 for the latitude.
:?: Why isn't it +90° to -90° latitude?? And what do you mean with "more or less"?

Zitat

Using custom map type approach, the tile border coordinates are automatically computed by the zoom level.
Very interesting info!

Zitat

has not a corresponding tile on the default map tile set. The closest is probably the tile 15,12 (03311 in QuadTree) as you can see in this picture. There are differences in both lat (4 degrees) and long (2 degrees), and these are the differences I experienced placing your AvA tile as 03311 on usnb map.
Allright. I wish I had known this in the beginning of the DG project... Ok, now we have to live with this. So there have to be two tile sets: one for Google Earth and one for Google Maps! (if we want to use the custom map feature)

Zitat

I don't know much about google earth, but probably its custom tile settings works like custom tile layer in Google Map.
As to my best knowledge, it's not possible to use custom tile layers with Google Earth Free-Version.


Zitat

To solve the situation I think there are several approaches:

1. using the tile overlays approach in Google Map (but I don't like this, because this means poor performance and difficulties adding another overlays if needed)
2. re-cut the official tile set in order to map the tiles as per official Google tile set and adopt the custom map type approach (I prefer this approach, but I think you must do some tests on Google Earth too


I also prefer approach 2. That means: A new "Schnippselorgie" (cutting orgy)! :mrgreen:
(I think, there is no need to do testing in Google Earth: The tiles there we leave unchanged.)

OK, let's do it! :D

The plan:
  • Assign a aventuria map in photoshop, which have the correct dimensions: a square, right?!
  • So I will fill up the ocean in the east and west with blue color
  • But I have to be carefull! The position of aventuria should fit exactly to the position in google earth DG.
  • What would be the best method to take care of this?

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Viridovix

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Montag, 15. Februar 2010, 16:52

Re: DereGlobus Maps

(Thanks for post moving!)

Your plan seems ok, but because I'm working on some modification of my Tile Cutter to take in account an offset that will be able to resolve such problem, let me try to complete the code: then I will made some tests on the official tileset and I will release the cutter to Dere Globus community. This can be useful for all the custom map available by the community.

At the moment, the Tile Cutter works on the picture of the map at given zoom level (say zoom level 10) and cut all the tiles for each level from 10 to 0 (whole world) using the Google Map notation (i.e. x_y_zoom.jpg) instead of QuadTree notation (but I can add this feature too).

Zitat

Why isn't it +90° to -90° latitude?? And what do you mean with "more or less"?
This is due to the Mercator Projection: the math is explained here http://en.wikipedia.org/wiki/Mercator_projection. You can notice that there is a section explaining the ±85.05113° range in latitude.

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Dienstag, 16. Februar 2010, 00:28

Re: DereGlobus Maps

Zitat

I made a C# program able to re-create the tiles accordingly to the default tile scheme of Google Map, I'll try on your tiles to make everything works in Google Map Custom Map too...

Zitat

Your plan seems ok, but because I'm working on some modification of my Tile Cutter to take in account an offset that will be able to resolve such problem, let me try to complete the code: then I will made some tests on the official tileset and I will release the cutter to Dere Globus community. This can be useful for all the custom map available by the community.
This sounds awesome! :D

Is the Tile Cutter the same as this C# program?
What is the functionallity of this program?
What is the input and the output?

Zitat

At the moment, the Tile Cutter works on the picture of the map at given zoom level (say zoom level 10) and cut all the tiles for each level from 10 to 0 (whole world) using the Google Map notation (i.e. x_y_zoom.jpg) instead of QuadTree notation (but I can add this feature too).
Well, if we use different tile sets vor maps and earth, I don't care about the notation.

You are saying: "The whole world". So there would be a great amount of empty 'grey' space arround aventuria, right?
Because I think it would be not simple to include fanmade maps of the region behind the bronze sword (Riesland) or Myranor (Güldenland) in the west, because of very different resolutions. So a whole worldmap in one piece is not possible - also because of memory requirements!

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Dienstag, 16. Februar 2010, 20:33

Re: DereGlobus Maps

You're right... I was unclear.

As example, we can suppose that we want to create the map for the whole Europe. We have several images, say, for Spain, French, Italy, Germany.... at the same zoom level, say 10

To have the images correctly placed in respect of geographical coordinates (ie. for Spain, Madrid must have the coord. 40.41807,-3.673725) with the actual version of Tile Cutter I must manage each single image in a way that the upper left corner can be the left corner of a default tile and the size of the picture must be a multiple of 256 pixel. [1]

So, starting for instance from Spain, I can obtain all the tiles related to Spain from zoom level 10 to 0. Of course, this is not the right way, because at low zoom level, we need French, Germany and Italy to paint the whole Europe. Thus, we can create say, levels from 10 to 8 for French, Germany, Italy, Spain... then put togheter all the pieces at zoom 8 and restart from zoom 8 to 5 and so on.

Basically, what we did for AVenturia:

1. scan the original maps in the same resolution.
2. evaluate, based on scale available on the map, the Google Map zoom level of such images - assuming level 10
3. join togheter all the map, obtaining large square images of 4096x4096 pixel (thus 16x16 tiles), evaluating the correct position (i.e. Vinsalt at 0° in longitude)
4. apply the tile cutter on each square image until we reach 256x256 (i.e. one tile), thus level 6
5. join togheter the tiles of level 6
6. apply again the tile cutter

Because we are working on just a continent (Aventuria) of the whole Dere, at each zoom level we don't have all the tiles to cover all the world. At zoom level 0 we can have a basically grey tile, with just a small area in green and blue :-)

Thus, some pitfall must be avoided:

1. when a tile is not available, you have a 'silent' error on url request (resource not found) but you can manage this with a tile server that check if there is a jpg file for the requested url, and in case it is missing, i can return an "hic sunt leones" (i.e. "no data") tile.

2. when you add new map region, probably you must recreate part of lowest zoom level tiles (i.e. at level zero, the small area in green and blue is expanding). This can be easily do if you have an efficient and easy to use Tile Cutter. I'm working on it.

----
[1] Because the Mercator Projection and the Google Map tile schema it is possible to evaluate, for each given zoom level from 0 to, say, 17, all the pixel per degree resolution. When this is known, it is possible to give the coordinate of map boundary and the Tile Cutter can add pixel strip as required, without manual operation.

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Thamor

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17

Mittwoch, 17. Februar 2010, 19:47

Re: DereGlobus Maps

Zitat

Thus, we can create say, levels from 10 to 8 for French, Germany, Italy, Spain... then put togheter all the pieces at zoom 8 and restart from zoom 8 to 5 and so on.
Nice trick! So we don't need to handle whole highresolution worldmaps.

Zitat


1. scan the original maps in the same resolution.
2. evaluate, based on scale available on the map, the Google Map zoom level of such images - assuming level 10
3. join togheter all the map, obtaining large square images of 4096x4096 pixel (thus 16x16 tiles), evaluating the correct position (i.e. Vinsalt at 0° in longitude)
4. apply the tile cutter on each square image until we reach 256x256 (i.e. one tile), thus level 6
5. join togheter the tiles of level 6
6. apply again the tile cutter
Allright.
  • Step 1 is done allready (of course^^).
  • Step 3: Ok, but I think Vinsalt (by the way at -0.57, 25.6) is not the best reference point, because
    [list] a) It's on an "old map" of the Kartenwerk
    b) Citys have a very big red dot, this cause inaccuracy[/list]
    We should take many referencepoints, perhaps capes
  • Step 4: Ok, so the tile cutter cut down a big map to small tiles? (really?) I've done this - easily! - with photoshop macros. So perhaps the TileCutter is not necessary at all? :roll:


Zitat

1. when a tile is not available, you have a 'silent' error on url request (resource not found) but you can manage this with a tile server that check if there is a jpg file for the requested url, and in case it is missing, i can return an "hic sunt leones" (i.e. "no data") tile.
Im glad, you are so experienced in this tasks!

Zitat

2. when you add new map region, probably you must recreate part of lowest zoom level tiles (i.e. at level zero, the small area in green and blue is expanding). This can be easily do if you have an efficient and easy to use Tile Cutter. I'm working on it.
Ok, that's fine, so the TileCutter brings much convenience.

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Viridovix

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18

Mittwoch, 17. Februar 2010, 23:09

Re: DereGlobus Maps

mmm... € 1.018,80 in Italy: Photoshop is a little bit expensive for me ;-)

The Tile Cutter is free...

I'd take a look at photoshop script, to check if it was portable to GIMP but the structure of GIMP is quite different from Photoshop... thus I preferred to manage my own code via C#

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Viridovix

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19

Dienstag, 6. April 2010, 17:17

Re: DereGlobus Maps

Well, the tile cutter is ready and it works fine, with offset computing and resolution check to desume the best zoom level for a given map.

To check it with your map I put togheter your tiles (I haven't the full map) with two digit (i.e. from AvA11 to AvF44) obtaining a 2048 x 3072 pixel (i.e. 8 x 12 tiles) map. Because of coords you stated for map boundary, this seems tho show a little difference in north/south (lat) vs east/west (lng) resolution:


Quellcode

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Long
----------
Pixel: 2048
Max. Lng.: 13,8295118725761
Min. Lng.:  -8,92879521172979
Diff. Lng.: 22,7583070843059
Pixel per degree: 89,9891188045485

Lat
----------
Pixel: 3072
Max. Lat.: 44,6852318217399
Min. Lat.:  13,8321147025536
Diff. Lat.: 30,8531171191863
Pixel per degree: 99,5685456394177


The data show that such map is close to zoom level 7, which requires a 91,02222 pixel per degree.

Computing by tile cutter and google maps api, we obtain that a map with your coords must be 2071 x 3285 pixel thus a little stretch is required, to respect your boundaries AND the mercator projection.

I try to put all togheter in this link: http://maps.usnb.it/dg.html

Here you can see:

1. grey area: this indicates area for which no tiles are provided;
2. map area: your map, placed on the right coordinates for boundaries (check the marker at top left corner and bottom right corner);
3. black area: the offset added to map boundary in order to have a tile set compatible with the google map tile coordinates system;
4. several marker of some towns placed at coordinates obtained by Dere Globus Google Earth. These markers show latitude errors that are greater in the middle of the map and smaller at top and bottom (I discuss this in the follow);

What you can do:

1. zoom out until level 0 (i.e. the whole world);
2. click on the map obtaining the point lat lng coordinates, the tile coordinates and the zoom level.

Regarding the lat error this can be due to several fact:

1. I retrieve the town coordinates from Google Earth, thus probably an error is introduced
2. When Google Earth place custom tiles on the world, it introduce some kind of distortion

Due to the fact that the error curve is parabolic, probably this is introduced by the Spherical Mercator instead of Ellipsoid Mercator (i.e. accuracy is related to the fact that the Earth is not spherical, but it is an ellipsoid); this error is really small at high zoom level (i.e. 10 and above) and can be higher at low zoom level (i.e. 0 to 10). Of course, it is affected by the original map zoom level. Probably, starting the cutting from a map taken at 10 zoom level, the results will be better... Google Maps assume spherical mercator, probably Google Earth is ellipsoid?

I must check at Google Earth to learn how it manages the tiles and mercator projection. This is a picture with the error distribution:
»Viridovix« hat folgende Datei angehängt:
  • errors.png (58,19 kB - 336 mal heruntergeladen - zuletzt: 7. November 2013, 21:32)

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Viridovix

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20

Mittwoch, 7. April 2010, 00:38

Re: DereGlobus Maps

It WORKS!!!

Take a look here now: <a class="postlink" href="http://maps.usnb.it/dg.html">http://maps.usnb.it/dg.html</a>

So, at the end... :-)

Of course... Lat Lng are computed accordingly with WGS84 (geodetic) and tiles are computed accordingly with EPSG:900913 (Spherical Mercator)... just a little modification in a formula and all the tiles are cutted accordingly...

Now we can have just one Lat Lng data set and two drawing systems...

Tschuss...

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