Although the key is illegible, I will take your word that the color gradations go from -25 to 100 and that there are 5 colors. OK so far? So that means each color has an undifferentiated range of 25 ft, still OK? That means, then, that simply within each color, your chart measurement has a possible error of from 1 to 25 ft.
Note, if the entire chart is only showing 125 ft, of which only 100 is above 0,...
To clarify, the color gradations for the entire map cover a much wider range. The five colors representing the range from -15 to 100 are the colors in which the debris field are depicted, clearly indicating debris heights ranging from at the very minimum, -6 to 76 feet, which is at least six stories.
...the chart contains a built in error rate of 25%
This is not an error rate, simply a decision to limit the resolution of the color scheme employed by the cartographers to make the map easier to read. A higher resolution of height data is used in the shading algorithm which visually conveys the slopes of the surface.
(Have you ever used a U.S. Geological Survey contour map? It's typical to have contour lines at 100-foot elevation intervals, but that does not mean that there is any 100-foot error in the data.)
Typical aerial LIDAR survey accuracy for height in 2001 was approximately +/- 3 inches. I have inquired at CARSI what the accuracy of the 9/19/01 Ground Zero survey is, for both height and ground-plane position. (And also, whether any higher resolution renderings and/or the raw numeric height field data are available.) I'll let you know any responses I receive.
That is useless information, in my view.
Our views are no one's concern but our own. What's important is the case you can make based on rational evaluation of evidence.
What those of you who need this chart to work for you might do, is correlate specific areas of it to some of the better photographs posted on earlier pages of this thread. This assumes, of course, that there exists a genuine interest in knowing the height of relevant areas of GZ.
Perhaps all of us can step back here and ask ourselves whether, within this thread, there exists sufficient data to advance the state of knowledge on the issue of GZ's height?
No, we do not have to do any such thing. The direct height measurements via LIDAR have precedence over indirect measurements from photographs. There is no advancing the state of GZ's height beyond the LIDAR maps unless more accurate direct height measurements exist.
However, if
you wish you can attempt to cast doubt on the accuracy of the LIDAR measurements by showing that they are inconsistent with heights shown in photographs. This would require photographs carefully documented as to date, and careful photometric analysis of them shown step by step so that the methods and calculations can be verified by others. Such analysis typically includes establishing each camera's location, view angle, and focal length based on multiple fixed landmarks whose positions are themselves established by an accurate spatial map (I'd suggest CARSI's NYCMap for this purpose.) Even then, establishing the exact horizontal position and height of a point in the rubble simultaneously (which is 3 unknowns, with only 2 pieces of data to determine them from, the coordinates of the point in the photo image) is going to be a challenge. You'll have to identify the same point in 2 or more photographs taken from different viewpoints and do some math. I doubt that you'll be able to approach the likely (pending verification from CARSI) +/- 3 inch accuracy of the LIDAR data but if there are major inconsistencies in the map you should be able to show them. If you want to do this I'll help examine the results, but the burden of proof for such a claim would be on you and I'm not interested in doing your work for you.
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For those interested in post-9/11 cartography, I'd like to correct an error in an earlier post. I provided what I stated (and thought) was a link to CARSI's page of other Ground Zero mappings and images, but it turns out that page doesn't have its own url so the link went only to CARSI's home page. To see the many fascinating map images, go to
http://www.geo.hunter.cuny.edu/~carsi/, then click "Presentations" on the site menu bar, then click the "Woodward Gallery: Charting Ground Zero" link, and finally the "click link to view images" link at the top of the page.
Respectfully,
Myriad
