Charts

[sidetrack]

A few comments and questions on the New Zealand charts that a lot of you are experimenting with...

Firstly, I'm in Tonga waiting for a weather window to sail to NZ and I'm very interested in trying out OCPN as at least a backup tool for the trip. Makes me smile to see that these are the charts you've chosen to try adding.

Second, Did LINZ ever come back with an answer about allowing OCPN to decrypt their RNC charts. I saw a couple of posts, but no update.

Third, I'm reading through the process you've been employing to geo-reference the tif files and make them available to OCPN. I'm familiar with Seaclear/Mapcal, so I think I'll be able to get it going. Actually I had already MapCaled some of the NZ charts a while back, in advance of my South Pacific crossing. In the event I don't manage useful results right off has anyone converted any of the relevant charts between say the Vava'u group in Tonga and Opua in NZ... I'd love to have them to play with on the trip down.

And last but not least, there is a link on the OpenCPN site that points to freeboatingcharts.com . I've checked out the site briefly and it doesn't seem to be a valid resource for finding charts. Has anyone had more luck with it than me?

[GPS-Marco]

Originally Posted by sidetrack

A few comments and questions on the New Zealand charts that a lot of you are experimenting with...

Firstly, I'm in Tonga waiting for a weather window to sail to NZ and I'm very interested in trying out OCPN as at least a backup tool for the trip. Makes me smile to see that these are the charts you've chosen to try adding.

Second, Did LINZ ever come back with an answer about allowing OCPN to decrypt their RNC charts. I saw a couple of posts, but no update.

Third, I'm reading through the process you've been employing to geo-reference the tif files and make them available to OCPN. I'm familiar with Seaclear/Mapcal, so I think I'll be able to get it going. Actually I had already MapCaled some of the NZ charts a while back, in advance of my South Pacific crossing. In the event I don't manage useful results right off has anyone converted any of the relevant charts between say the Vava'u group in Tonga and Opua in NZ... I'd love to have them to play with on the trip down.

And last but not least, there is a link on the OpenCPN site that points to freeboatingcharts.com . I've checked out the site briefly and it doesn't seem to be a valid resource for finding charts. Has anyone had more luck with it than me?

Hi. Let me express my "envy"... I'm in front of a PC, in a house in Rome, it's raining and tunderstorming all around and tomorrow, when it will be finished, I'll go to my office!

Well, my dear friend in the other side of the world, I'd like to georef a chart for you. I'll try to think I'm sailing in the south seas... I just need an input: Can you give me the chart number?

These are the charts in the NZ web site: charts.linz.govt.nz - /tifs/

(and this is the selection page, as you know better than me: Chart Images)

Which one would you like to see geo-referenced and BSBed?

Ciao, and fair winds...

Marco.

[dacust]

Originally Posted by GPS-Marco

Also VER/2.0 is accepted by seaclear.

Marco.

A coupla updates ago I added the VER/2.0 to it, so if it still doesn't read it, then there is something else...

-dan

[sidetrack]

Originally Posted by GPS-Marco

Hi. Let me express my "envy"... I'm in front of a PC, in a house in Rome, it's raining and tunderstorming all around and tomorrow, when it will be finished, I'll go to my office!

Well, my dear friend in the other side of the world, I'd like to georef a chart for you. I'll try to think I'm sailing in the south seas... I just need an input: Can you give me the chart number?

These are the charts in the NZ web site: charts.linz.govt.nz - /tifs/

(and this is the selection page, as you know better than me: Chart Images)

Which one would you like to see geo-referenced and BSBed?

Ciao, and fair winds...

Marco.

Thank you very much Marco,
Your envy is shared, I'd love to get to Rome. Tonga is beautiful and
very friendly, I can heartily recommend a visit. Also there is a shortage of Italian sailors here, this season, you need to come and represent them.

I'd love to have NZ 14605 it covers a good overview of the route. If you could do that one for me it would be a great example for me. Actually I'm wondering if this is sourced from a NOAA chart like some of New Zealands other international charts, maybe I could directly download the BSB?

Other than that, there are a lot of smaller areas along the route and I'm gong to try my hand at some more specific charts:
NZ 14638
NZ 22
NZ 223
NZ 51

NZ 512
NZ 5125
NZ 82
BA 968 (British Admiralty Chart, anyone know where to download an image or RNC?)

Otherwise, fantastic work everyone. I'm doing a lot of reading to catch up with everyone.

-Erik

[sinbad7]

Needed a smaller scale chart of the English Channel and found this satellite map through a 'google'. Difficult to calibrate 100% owing to lacking distinct land marks but good enough for an overview.

[sinbad7]

Erik..

Have a look this NOAA list at the end..

[sidetrack]

Hey Marco,


Were you able to try NZ14605? I stepped through the process and successfully got it into OpenCN (Thank you everyone for the great work and instructions), but I had difficulties on the Mapcal side of it.


1) Setting points on a chart that crosses Longitude 180 confused Mapcal and I had to get creative with the calibration points. I got through that alright and got good longitude on the chart but...


2) The latitude didn't map to the chart correctly. It is OK at the calibration points, but skews rapidly as you get away from them. The chart says it's Mercator Projection, I'm not sure what the problem is. Am I messing up with Mapcal, or are you seeing the same thing? Have any of the other NZ charts shown similar issues?


Sinbad, thanks for the link... doesn't appear that Minerva reef is in the NOAA charts, must be strictly British Admiralty.


-Erik

[GPS-Marco]

Originally Posted by sidetrack

Hey Marco,


Were you able to try NZ14605? I stepped through the process and successfully got it into OpenCN (Thank you everyone for the great work and instructions), but I had difficulties on the Mapcal side of it.


1) Setting points on a chart that crosses Longitude 180 confused Mapcal and I had to get creative with the calibration points. I got through that alright and got good longitude on the chart but...


2) The latitude didn't map to the chart correctly. It is OK at the calibration points, but skews rapidly as you get away from them. The chart says it's Mercator Projection, I'm not sure what the problem is. Am I messing up with Mapcal, or are you seeing the same thing? Have any of the other NZ charts shown similar issues?


Sinbad, thanks for the link... doesn't appear that Minerva reef is in the NOAA charts, must be strictly British Admiralty.


-Erik

Hi Erik, I found the same problem for NZ14605 as you in MapCal (the problem of crossing 180° longitude). But I found a trick. Moreover I found some problems in showing the chart in OCPN. This are the posts about that

The problem #233
The header I'm using #235
The OCPN Bug and the trick to use in Mapcal #237

Of course you can take the calibration heder from Thomas (#236).

I'm trying to have the OCPN bug corrected. I'll try to calibrate other NZ maps.

It would be great to create a Data Base of Heders so that we all can access info, not duplicate work, create our maps by ourself, cross check the correctness of calibrations and trust them a bit more (like a "Tested Calibration" stamp). Someone should provide a little space to store headers and we should think to a test process...

Ciao, Marco.

[sidetrack]

Originally Posted by GPS-Marco

Hi Erik, I found the same problem for NZ14605 as you in MapCal (the problem of crossing 180° longitude). But I found a trick. Moreover I found some problems in showing the chart in OCPN. This are the posts about that

The problem #233
The header I'm using #235
The OCPN Bug and the trick to use in Mapcal #237

Of course you can take the calibration heder from Thomas (#236).

I'm trying to have the OCPN bug corrected. I'll try to calibrate other NZ maps.

It would be great to create a Data Base of Heders so that we all can access info, not duplicate work, create our maps by ourself, cross check the correctness of calibrations and trust them a bit more (like a "Tested Calibration" stamp). Someone should provide a little space to store headers and we should think to a test process...

Ciao, Marco.

Ahh, I used the same trick. I found it useful to set a point at the NE corner of the chart, and then at the intersection of the S edge and 180E. the rest of the points snapped in with good approximate positions and the 180+E latitudes calculated.

I hadn't tried panning across 180, I experience the a similar Bug effect as I do.

What troubles me is the extensive number of cal points needed to get the latitude to display properly. With a quick 4 corner calibration I find my gps position 55nm off of the charted position. I see that again now as I try to calibrate NZ21. No matter how many points I put in, it still seems to skew the latitude in between them, as if it were expecting a different Projection. Do you see the same thing? Has that been typical with calibrations of charts in other parts of the world?

The only others I've done have been Sea of Cortez charts and I don't remember having such huge variations in latitude.

[GPS-Marco]

Originally Posted by sidetrack

Ahh, I used the same trick. I found it useful to set a point at the NE corner of the chart, and then at the intersection of the S edge and 180E. the rest of the points snapped in with good approximate positions and the 180+E latitudes calculated.

I hadn't tried panning across 180, I experience the a similar Bug effect as I do.

What troubles me is the extensive number of cal points needed to get the latitude to display properly. With a quick 4 corner calibration I find my gps position 55nm off of the charted position. I see that again now as I try to calibrate NZ21. No matter how many points I put in, it still seems to skew the latitude in between them, as if it were expecting a different Projection. Do you see the same thing? Has that been typical with calibrations of charts in other parts of the world?

The only others I've done have been Sea of Cortez charts and I don't remember having such huge variations in latitude.

Erik, I experienced similar problems as you for NZ21. I used only 4 calibration points (2 on the north and 2 on the south part of the map, each couple at the same latitude), and this is the header:

! Created by mc2bsbh-0.00.01 - Use at your own risk!
VER/2.0
BSB/NA=Norfolk Island to Cape Egmont
    NU=NZ21 (INT641),RA=8504,12992,DU=324.67
KNP/SC=1500000,GD=WGS84,PR=MERCATOR
    PP=-23,PI=UNKNOWN,SP=UNKNOWN,SK=0.0
    UN=METERS,SD=LAT,DX=117.35,DY=117.35
REF/1,2381,1213,-28.000000000000,170.000000000000
REF/2,8032,1213,-28.000000000000,177.000000000000
REF/3,8033,10816,-38.000000000000,177.000000000000
REF/4,766,10814,-38.000000000000,168.000000000000
PLY/1,-27.4337865061844,168.500379768393
PLY/2,-28.5337923865424,168.500385340842
PLY/3,-28.5340926714463,167.63397074106
PLY/4,-39.4354221867463,167.635152939466
PLY/5,-39.4333141875708,176.999983322162
PLY/6,-27.4333188369391,176.99998785172
DTM/0,0

well, OCPN does not (or cannot?) handle mercator projection correcly. I found up to 8 miles error in the center of the map, zero error at the latitudes of the couples of calibration points, and 2/4 miles error on the extreme north/south of the map. Error is always in latitude, always zero error in longitude.

Well, I think that the problem is in how OCPN renders images. As you know in mercator projection the X is proportional to longitude while the Y is not proportional to latitude (see link for details http://en.wikipedia.org/wiki/Mercator_projection )

Maybe it is an OCPN bug, maybe is not possible a perfect render for some strange reason. I'aa also ask in the Tecnical thread.

Ciao, Marco.

[sidetrack]

Originally Posted by GPS-Marco

I found up to 8 miles error in the center of the map, zero error at the latitudes of the couples of calibration points, and 2/4 miles error on the extreme north/south of the map. Error is always in latitude, always zero error in longitude.

Well, I think that the problem is in how OCPN renders images. As you know in mercator projection the X is proportional to longitude while the Y is not proportional to latitude (see link for details http://en.wikipedia.org/wiki/Mercator_projection )

Maybe it is an OCPN bug, maybe is not possible a perfect render for some strange reason. I'aa also ask in the Tecnical thread.

Ciao, Marco.

Good to know it's not just me seeing it. That explanation of the Mercator projection makes sense also.

Reading one of the other posts you linked leads me to believe that It's the scale that's causing more error than I've seen before. All my other calibrations were much smaller charts. Looks as if I'll have to plug in a lot of calibration points to get something useable.

I don't think there is anything wrong with OCPN, because I see the same thing in MapCal before I ever transfer anything over.

The charts seem to have a fairly linear N-S scale, I just expected that MapCal would compensate for it.

-Erik

[bdbcat]

GPS-Marco....


Could you please send me copies of two charts having problems:

1. NZ21 (georef problems with 4 REF points).
2. Whichever chart you created (cannot find the thread) which was non-rectangular and had problems with 180 E/W crossing and usable outline. Maybe it is NZ14605?

I'll take a look at these and report back.

Thanks
Dave

[cagney]

Dave
Marco and I discussed this in the beta test thread.It was indeed about NZ14605. Check the links in Marcos post.

Sidetrack and others. I have by now done quite a few NZ charts from large scale harbor plans to very small scale planning charts -- 1:10,000,000 and found my own way of working with georeferencing. I don't use MapCal, not sure what I will gain in the end.
Because of hardware problems with big tiffs I use the admirals computer with XP and Paint to do the pixel/Lat&long connection. Then I handcraft the required header file base on a template where ofcourse a few values have to be adjusted and the REF:s and PLY:s done.
For chart of 1:400,000 and larger a REF/ in each corner is enough.
The same points are used for PLY/:s. For charts between 1:1,500,000 and 1:3,500,000 I map 40 - 50 REF:s.No shortcuts available here. Check a NOAA chart for reference. Once again I start with the 4 corners, again, these are used for PLY:s as well. Then I use the intersections between every 5 or 10 degrees of lat & long and respective intersection with the chart borders as further REF:s.
This is not as hard to do as it sounds. Once you have done all longitudes on a given latitude, it is a matter of copying and pasting. This is an area where Linux is way faster than Win. Mark(paint) what you want to copy, this actually in itself copies the text to a buffer, then put the cursor where you want the insert and middle-click. Thats it. Then of course you have to change the latitude and pixel height(length) on every copied line.
For an illustration check this post.
It's worth to repeat that Dave probably introduces a new algorithm in the next beta for charts of 1:5,000,000 or smaller. This will require only 4 REF:s, once again best with one in each corner, but will not be as accurate as the present formula with a zillion REF:s. It will roughly be similar to the accuracy of a pencil line on a corresponding paper chart. As these charts are for general overview and planning purposes this accuracy should be OK.

Thomas

[GPS-Marco]

Ok, I've prepared the NZ21 header. My idea is to create an header web page, so people can take the headers, download the maps, crate by themselves the bsb chart and use the chart in OCPN. I ask you to try this header and give me comments. I've put as may ref as possible in latitude to minimize OCPN rendering distorsion so it should work fine.

! Download chart http://charts.linz.govt.nz/tifs/nz21.tif
! Check MD5 of chart against the following
! MD5SUM 5dd9bd1a3bb72e2f69424a444b086671
! Create BSB chart using tif2bsb from libbsb
VER/2.0
BSB/NA=Norfolk Island to Cape Egmont
    NU=NZ21(INT641),RA=8504,12992,DU=341.276
KNP/SC=1500000,GD=WGS84,PR=MERCATOR
    PP=-23,PI=UNKNOWN,SP=UNKNOWN,SK=0.0
    UN=METERS,SD=MEAN LOW WATER SPRINGS,DX=111.64,DY=111.64
CED/SE=2005,RE=43,ED=2009
REF/1,8032,1213,-28.000000000000,177.000000000000
REF/2,8033,10816,-38.000000000000,177.000000000000
REF/3,768,10816,-38.000000000000,168.000000000000
REF/4,767,12293,-39.433333333333,168.000000000000
REF/5,768,8802,-36.000000000000,168.000000000000
REF/6,767,6840,-34.000000000000,168.000000000000
REF/7,768,4924,-32.000000000000,168.000000000000
REF/8,767,3050,-30.000000000000,168.000000000000
REF/9,472,2127,-29.000000000000,167.633333333333
REF/10,471,1214,-28.000000000000,167.633333333333
REF/11,471,700,-27.433333333333,167.633333333333
REF/12,8033,699,-27.433333333333,177.000000000000
REF/13,8032,2127,-29.000000000000,177.000000000000
REF/14,8033,3049,-30.000000000000,177.000000000000
REF/15,8033,3982,-31.000000000000,177.000000000000
REF/16,8033,4924,-32.000000000000,177.000000000000
REF/17,8033,5877,-33.000000000000,177.000000000000
REF/18,8034,6841,-34.000000000000,177.000000000000
REF/19,8033,7815,-35.000000000000,177.000000000000
REF/20,8033,8802,-36.000000000000,177.000000000000
REF/21,8033,9802,-37.000000000000,177.000000000000
REF/22,8033,11844,-39.000000000000,177.000000000000
REF/23,8033,12292,-39.433333333333,177.000000000000
REF/24,471,11843,-39.000000000000,167.633333333333
REF/25,471,9802,-37.000000000000,167.633333333333
REF/26,472,7815,-35.000000000000,167.633333333333
REF/27,472,5877,-33.000000000000,167.633333333333
REF/28,471,3983,-31.000000000000,167.633333333333
REF/29,3997,699,-27.433333333333,172.000000000000
REF/30,3996,1213,-28.000000000000,172.000000000000
REF/31,3996,3050,-30.000000000000,172.000000000000
REF/32,3996,4924,-32.000000000000,172.000000000000
REF/33,3996,6840,-34.000000000000,172.000000000000
REF/34,3996,8803,-36.000000000000,172.000000000000
REF/35,3996,10816,-38.000000000000,172.000000000000
REF/36,3996,12293,-39.433333333333,172.000000000000
PLY/1,-27.4331513422981,168.508334881964
PLY/2,-28.5646616764591,168.508358006692
PLY/3,-28.5624483698463,167.633461651226
PLY/4,-39.4337495987743,167.633332819783
PLY/5,-39.4333333333333,177
PLY/6,-27.4333333333333,177
DTM/0,0

Ciao, Marco.

[GPS-Marco]

Same as previous post, but for NZ51
Ciao

! Download chart http://charts.linz.govt.nz/tifs/nz51.tif
! Check MD5 of chart against the following
! MD5SUM ffc37051a7153af55c0392cf22fa95dc
! Create BSB chart using tif2bsb from libbsb
VER/2.0
BSB/NA=Tauroa Point to Cape Brett
    NU=NZ51,RA=12510,8383,DU=276.087
KNP/SC=200000,GD=WGS84,PR=MERCATOR
    PP=-41,PI=UNKNOWN,SP=UNKNOWN,SK=0.0
    UN=METERS,SD=MEAN LOW WATER SPRINGS,DX=18.4,DY=18.4
CED/SE=2001,RE=64,ED=2008
REF/1,2786,7916,-35.200000000000,173.000000000000
REF/2,1130,4698,-34.666666666667,172.666666666667
REF/3,1130,2698,-34.333333333333,172.666666666667
REF/4,1130,706,-34.000000000000,172.666666666667
REF/5,4441,6706,-35.000000000000,173.333333333333
REF/6,4441,4698,-34.666666666667,173.333333333333
REF/7,1130,7917,-35.200000000000,172.666666666667
REF/8,6097,4699,-34.666666666667,173.666666666667
REF/9,6098,2697,-34.333333333333,173.666666666667
REF/10,6098,706,-34.000000000000,173.666666666667
REF/11,4442,7917,-35.200000000000,173.333333333333
REF/12,11066,7916,-35.200000000000,174.666666666667
REF/13,11066,6706,-35.000000000000,174.666666666667
REF/14,11066,4698,-34.666666666667,174.666666666667
REF/15,11066,2697,-34.333333333333,174.666666666667
REF/16,11066,705,-34.000000000000,174.666666666667
REF/17,7754,7917,-35.200000000000,174.000000000000
REF/18,7754,6706,-35.000000000000,174.000000000000
PLY/1,-33.9600004789198,172.5333333482
PLY/2,-34.716683946132,172.53333291407
PLY/3,-34.7166879878263,172.783332556744
PLY/4,-34.8900228358421,172.783333258871
PLY/5,-34.8900162427284,172.89166679185
PLY/6,-34.9533466821481,172.891666996924
PLY/7,-34.9533453082201,173.016667164153
PLY/8,-35.2000000038664,173.016666666999
PLY/9,-35.200002110507,174.863333320874
PLY/10,-33.9599998484851,174.863333345041
DTM/0,0