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PostPosted: 12 Jan 2019 00:48 
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Joined: 30 Jan 2011 13:03
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G'day all,

I am currently working on a project for a 'client' who has requested (and kindly supplied) the so-called "Valuation Maps" for me to include with the usual Topographic maps that I would otherwise provide as 'ground textures' on the route. Now, I appreciate that there may not be any other way than to manually georeference these and I don't mind if that is the case, the issue that I have is that these maps have absolutely NO 'regulation' Geodetic Data in them. The only way I have found to georeference them is to examine the maps against a standard Topographic map of the same 'covered' area and to pick out specific points from the Valuation Map that correspond to the same points in the standard maps for which I can then determine the Northings and Eastings and use that data to georeference them. This is clearly a long and drawn out process and I regret to say, somewhat prone to error. I was wondering if anyone else out there, especially any of you fellow TransDEM users from "across the pond", has had experience with these maps and knows of some other way (in particular, a more accurate one) of doing this?

I would appreciate any help...

Jerker {:)}


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PostPosted: 26 Jan 2019 00:44 
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Joined: 30 Jan 2011 13:03
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G'day All,

Come now, gentlemen (and ladies), surely someone out there has had experience with "Valuation Maps". Two weeks have passed and not a word of reply, I find that quite unbelievable from this forum!!!

Jerker {:)}


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PostPosted: 12 Feb 2019 01:50 
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Joined: 30 Jan 2011 13:03
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G'day all,

Okay, so now I'm starting to panic! It's been a full calendar month since my original post and there is still no response. I haven't even received anything from our "fearless leader"! At the very least, I thought Roland would have had something to say about this (if you're out there, Roland, give me an "ahoy", so that we could at least talk about the subject)...

Jerker {:)}.


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PostPosted: 12 Feb 2019 08:53 
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Joined: 05 Jan 2011 16:45
Posts: 1158
Jerker wrote:
I thought Roland would have had something to say about this
I'm afraid I can't say anything about these maps as I have never seen them. And you already mentioned the standard procedure of using identifiable reference points on a second map... :|


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PostPosted: 15 Feb 2019 01:23 
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Joined: 30 Jan 2011 13:03
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G'day Geophil,

Thanks for getting back to me, Roland. Regrettably, those weren't the words I wanted to hear!! I am surprised to hear, though, that you are not at all familiar with "Valuation Maps". For your future information, here is one of the ones with which I am dealing (it is the first one for the small town of Bellows Falls in Vermont), as it comes to me from my client (in *.tif format)...

Image

...and here it is after being georeferenced and saved as a *.png (via the recommended method in TransDEM, of course)...

Image

...and finally with it displayed in TransDEM where it is supposed to be, along with the route polyline created from the accompanying Topographic maps (not displayed for clarity)...

Image

...as you can see, it is very close but in places where it matters (such as the North West corner), greater accuracy is required. Unfortunately, I have no idea where the point on the map labelled as the "Match Mark For Next Sheet" is meant to be "on the ground", so I cannot use it (as ideal as it would be) for georeferrencing that end of the map. All of the georeferencing points are in the middle area of the map (as you might well be able to gather), making the task of accurately georefrerencing it, difficult, to say the least...

...if you could offer any help, it would be greatly appreciated...

Jerker/Garry {:)}


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PostPosted: 16 Feb 2019 13:18 
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Joined: 20 Nov 2012 01:41
Posts: 65
Hi Jerker,

Nothing new to offer, but your method is exactly what I did several years ago with "Sanborn Maps":

http://guides.libraries.psu.edu/sanbornmaps

Not all are available online, but here's an area in Trenton, NJ from 1890 that is:

https://www.loc.gov/resource/g3814tm.g3814tm_g056391890/?sp=31

Similar to your "Valuation Maps", they provide highly detailed maps of smaller areas used for insurance purposes. If you can find one that shows rail lines (less likely) or yards/industry (more likely) in your area of interest, it's worth the effort to get them into TransDEM/Trainz. That site has changed since I was last there, so I don't know if you can download anymore or have to do screen captures and cut and paste.

For me, that effort involved many trial and error repetitions until I got it where I was happy with it! Trying to line up an 1890 map with modern day points was a definite challenge!

Andrew


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PostPosted: 21 Feb 2019 01:28 
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Joined: 30 Jan 2011 13:03
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G'day SharkNose,

Thanks for jumping in there. Also, many thanks for those links. I have worked with the Sanborn maps as well and I agree that it would be a real challenge to align their 'older' maps with modern day alterations! Regrettably, the decision to use the "Valuation Maps" was not mine to make and as much as I would prefer to use the 'Sanborns' (which are available for the areas I am 'modelling'), if for no other reason than their colourful presentation, that matter is 'out of my hands'. I have been giving the natter some thought after it occurred to me that the 'measurements' shown adjacent to the place on the map above which is marked as the "Match Mark For Next Sheet", is the distance of that point from the starting point of the line at the point marked as "Sta 0". Correct me if I am wrong but is that distance (marked on the map as "52+80") not actually 52 Chains, 80 Links? If that is the case, then I can convert that distance into 'feet' and using the polyline tool find the point along the line where it should be and with the coordinates for that point and two others, utilise the "Georeference with Triangle Networks" option, which might give me more accurate results. Knowing that "Match Mark's" coordinates will also help with subsequent maps...

...let me know what you think about this idea...

Jerker/Gazza {:)}


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PostPosted: 21 Feb 2019 23:21 
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Joined: 20 Nov 2012 01:41
Posts: 65
Your explanation of the Sta 0 to Sta 52+80 makes sense. I never know what measurements those 52+80 were in, but if what you say is correct, the length would be 3484.8 feet or 0.66 mile. I got those numbers from a conversion app on my iPhone. And I guess that is the distance along the mainline track (the one in bold?).

Andrew


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PostPosted: 22 Feb 2019 01:14 
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Joined: 30 Jan 2011 13:03
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G'day SharkNose,

Indeed, Andrew, if my PREsumption (let's not call it an ASSumption - you know what happens when you do that) is correct, then it does make sense. Is it really that long a distance (I haven't done the 'math', yet)? Actually, I have done the calculations, now and I see that the decimal place is, in fact, accurate at 0.8 feet, which I calculate to be a mere 100 thou more than 9 and 1/2 inches, so I can easily work with 3,484' 9.5" (or even just 9") and be confident that I am sufficiently accurate...

..In fact, I have just taken a look at the adjacent map provided by my client and the distance marked for the next "Match Mark For Next Map" (for map 3) is shown at 105+60 (it begins at 52+80, of course), which is, if you do the calculations (given that there are 100 Links in a Chain) exactly "52+80" + "52+80" (80 + 80 Links is equal to 1 Chain 60 Links and 52 + 52 + 1 = 105, making for a distance of 105 Chains 60 Links)!! I have a feeling I'm onto something, here!

Its an oddball distance and although the maps with which I am working date from 1964 (by which time they would have been 'taken' with a theodolite), the measurements would surely be retained for consistency from previous maps which would have been made when they really did measure things using a "Chain" that was 66 feet long. There's that number, again!! It has not gone unnoticed that the distance of 52 Chains 80 Links is equal to 0.66 Miles and that a Link occupies the same distance as 0.66 feet but I don't know if this actually means anything, if at all!...

...I now have an ongoing plan and I can return to my work, hopefully with a greater degree of accuracy...

Thank you all for your assistance...

Jerker/Gazza {:)}


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