Jump to content

 
Photo

ID projection from mid century map

- - - - -

  • Please log in to reply
10 replies to this topic

#1
David Medeiros

David Medeiros

    Hall of Fame

  • Validated Member
  • PipPipPipPipPipPipPip
  • 1,089 posts
  • Gender:Male
  • Location:Redwood City CA
  • Interests:Cartography, wood working, wooden boats, fishing, camping, overland travel, exploring.
  • United States

Can anybody help me ID the projection in this mid century race map? It's regional, Middle East through Asia. Lambert Azimuthal Equal Area  gets me close but the parallels in the map are curved more than the MAPublisher projection. Modifing the lattitude of origin doesn't seem to help.

 

Looking for other likely candidates, although I may just geo ref this anyway.

 

Thanks,

David

 

 

Attached Files


GIS Reference and Instruction Specialist, Stanford Geospatial Center.

 

www.mapbliss.com

 


#2
Melita Kennedy

Melita Kennedy

    Key Contributor

  • Validated Member
  • PipPipPip
  • 70 posts
  • Gender:Not Telling
  • Location:Redlands, CA
  • United States

My first thought was orthographic, centered around 30N,78E. Some of the graticules (120E, here's looking at you!) just don't fit though.

 

Melita



#3
ProMapper

ProMapper

    Master Contributor

  • Validated Member
  • PipPipPipPip
  • 216 posts
  • Gender:Female
  • Location:India
  • Interests:promapper@gmail.com
  • India

How about Stereographic, centered at meridien 80 and 20 parallel. See attached screen shot.....



#4
ProMapper

ProMapper

    Master Contributor

  • Validated Member
  • PipPipPipPip
  • 216 posts
  • Gender:Female
  • Location:India
  • Interests:promapper@gmail.com
  • India

How about Stereographic, centered at meridien 80 and 20 parallel. See attached screen shot.....

Attached Files



#5
Strebe

Strebe

    Key Contributor

  • Validated Member
  • PipPipPip
  • 86 posts
  • Gender:Male
  • Interests:Map projections. Snobby chocolate. Science in general.
  • United States

There’s a good reason you’re having trouble with this one. It’s poorly drafted and has acquired distortions both systematic and erratic on the way from drafting to JPEG. I believe the map and the graticule were drafted independently because the graticule doesn’t match the geography closely enough to call the entirety a credible construction. The apparent intent is a Bonne with an irresponsibly high parallel made standard.

 

— daan Strebe



#6
ProMapper

ProMapper

    Master Contributor

  • Validated Member
  • PipPipPipPip
  • 216 posts
  • Gender:Female
  • Location:India
  • Interests:promapper@gmail.com
  • India

Stereographic looks very close match in this one .......

Attached Files



#7
Strebe

Strebe

    Key Contributor

  • Validated Member
  • PipPipPip
  • 86 posts
  • Gender:Male
  • Interests:Map projections. Snobby chocolate. Science in general.
  • United States

Meridians and parallels not meeting perpendicularly is a dead give away that it does not intend to be a stereographic. From the period and nationality, Bonne makes sense and indeed it was the best least squares fit of the very many I tried. But in the end, it's simply not a coherent design. Regardless of what you start from you'd be doing a lot of rubber-sheeting and you still can't win because the geography doesn't quite match the graticule.

--daan Strebe
  • Melita Kennedy likes this

#8
David Medeiros

David Medeiros

    Hall of Fame

  • Validated Member
  • PipPipPipPipPipPipPip
  • 1,089 posts
  • Gender:Male
  • Location:Redwood City CA
  • Interests:Cartography, wood working, wooden boats, fishing, camping, overland travel, exploring.
  • United States

So I ended up rectifying it to the best fit I had at the time, the Lambert Azimuthal I mentioned orginally. I would have spent more time tracking down the correct projection if the original map mattered, but in this case I was just after the rough placement of the route lines in MAPublisher. It was close enough that it didn't warp that much to get the graticule and shorelines to fit, but as Strebe points out the interior geography was not as accurate. Some of it was most likely placed by eye over a regular map of the land.

 

Worked ok anyway. I appreciate the help. If I have time I'll try the othe rporjections mentioned just to know what it is.

 

David


GIS Reference and Instruction Specialist, Stanford Geospatial Center.

 

www.mapbliss.com

 


#9
ProMapper

ProMapper

    Master Contributor

  • Validated Member
  • PipPipPipPip
  • 216 posts
  • Gender:Female
  • Location:India
  • Interests:promapper@gmail.com
  • India

Meridians and parallels not meeting perpendicularly is a dead give away that it does not intend to be a stereographic.

You are right Strebe, I did not look at the projection angles so minutely. Bonne is surely the closest match with standard parallel set pretty high at 40. Though David is already done with it, I was exploring it for a bit of learning.....

 

I was wondering how you do the comparison with least squares. You will need the distances at various points, say the graticule crossings from a fixed point. Do you have a software or some ready made methodology to do such analysis? Please do educate us on it when you find time. Thanks, it was a good learning.

Attached Files



#10
sitesatlas

sitesatlas

    Master Contributor

  • Validated Member
  • PipPipPipPip
  • 184 posts
  • Gender:Male
  • Location:Madrid, Spain
  • Spain

For what it's worth, the map projection is tilted a few degrees, too. I've drawn the approximate center meridian of the projection as a purple line on the attachment. You can also tell it's been rotated by looking at the 50N latitude line: there's more of it on the left side of the center meridian than on the right.

Attached Files


Michael Borop
World Sites Atlas
http://www.sitesatlas.com

#11
Strebe

Strebe

    Key Contributor

  • Validated Member
  • PipPipPip
  • 86 posts
  • Gender:Male
  • Interests:Map projections. Snobby chocolate. Science in general.
  • United States

Meridians and parallels not meeting perpendicularly is a dead give away that it does not intend to be a stereographic.

You are right Strebe, I did not look at the projection angles so minutely. Bonne is surely the closest match with standard parallel set pretty high at 40. Though David is already done with it, I was exploring it for a bit of learning.....

 

I was wondering how you do the comparison with least squares. You will need the distances at various points, say the graticule crossings from a fixed point. Do you have a software or some ready made methodology to do such analysis? Please do educate us on it when you find time. Thanks, it was a good learning.

Sorry to get back to this so late. I have a lot of hacky functionality on top of Geocart for my own research purposes that is not refined enough for release to others. One of those is a least-squares analysis. I preprocess the image to reduce biases caused by linear distortions (stretch, affine, rotation), insofar as they are clearly due to inaccuracies in image reproduction or warpage in the medium. Thus rectified, I state the cartesian coordinates of the graticule intersections. Then I just let Geocart churn through a large list of plausible candidate projections. For each, I use a root-finding algorithm to let Geocart adjust the scale of the candidate projection until its least-squares deviation from the image projection reaches a minimum. The candidate projection whose best least-squares deviation is the smallest of the lot wins.

 

That's the gist of it, but many projections are themselves able to be parameterized, and so this turns into more of a global minimization process, depending on what it is I am really trying to achieve. Usually there is a historical context attached to the image whose projection you are trying to identify, so if you are interested in the intent of the mapmaker (as opposed to just finding a projection that best fits the map), you would not add a projection developed in 1920 to the list of candidates if you know the map is from the 19th century. While I can come up with closer fits for this particular map through parameterizing, transforming, and mathematically distorting arbitrary projections, the historical context and the otherwise close fit of the Bonne clinches it. Also, the graticule deviates from the geography, so you'd have to decide which was more important to preserve if you were trying to reach a best fit, as opposed to reaching the mapmaker's intent.

 

-- daan Strebe


  • Mike Boruta likes this




0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users

-->