R CRS for Israel Transverse Mercator

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Keren Raiter

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May 22, 2019, 4:26:45 AM5/22/19
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Shalom,

Does anyone know of how I can reference the Israel Transverse Mercator (ITM, also called New Israel Grid, רשת ישראל החדשה) EPSG code 18204 in R?

I have spatial data in R that is currently in WGS1984, and I want to project it to ITM to calculate area accurately. 

Thanks for any assistance!
Keren


‫ב-5 באוק׳ 2018, בשעה 11:01, ‏‏אברהם פיינסילבר ‏<abe0...@gmail.com> כתב/ה:‬


הי עמית,

כבר ניסיתי בעבר את הפתרון הזה, ובעוד שהאפליקציה אכן מופעלת באופן מלא, היא לא שמישה מכיוון שכל המלל הופך להיות ג'יבריש...

תקן אותי אם אני טועה אבל מה שהתכוונת זה שאני אחליף את השורות:

knitr::knit2pandoc(input = rmdfiles,encoding = "UTF-8",quiet = TRUE)
includeMarkdown("C:\\Users\\ge_a\\Desktop\\test\\report_test.md")

ב- 
HTML(markdown::markdownToHTML(knit(rmdfiles, quiet = TRUE, encoding = "UTF-8")))

אבל זה לא פותר את בעיית הג'יבריש... יש לך הצעה?

סופ"ש נעים ותודה רבה!!

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Michael Dorman

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May 22, 2019, 6:36:14 AM5/22/19
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הרשת EPSG:18204 לא כלולה במאגר הרשמי, לכן המרה מ-WGS84 ל-ITM ע"י הערך המספרי 18204 תתן שגיאה שההגדרה של הרשת לא קיימת - 

Screenshot from 2019-05-22 13-28-37.png

אבל תמיד אפשר להשתמש גם הגדרת טקסט בפורמט ב-PROJ4, במקום בקוד EPSG. אם ידוע לך טקסט PROJ4 של רשת ישראל הספציפית שאתה צריך, אפשר לשים את הטקסט וזה יעבוד - 

Screenshot from 2019-05-22 13-30-35.png

ההגדרה הכי "טובה" של ITM שאני מכיר היא - 
"+proj=tmerc +lat_0=31.7343936111111 +lon_0=35.2045169444445 +k=1.0000067 +x_0=219529.584 +y_0=626907.39 +ellps=GRS80 +towgs84=-24.0024,-17.1032,-17.8444,-0.33077,-1.85269,1.66969,5.4248 +units=m +no_defs"
למרבה הצער יש מספר הגדרות שונות - עבודה עם ITM זה באופן כללי מתסכל... 


Keren Raiter

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May 22, 2019, 6:51:49 AM5/22/19
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Hi again,

I think I can answer this question myself now, based on an answer to a similar question on this group from 2015, posted by Michael Dorman - Thank you Michael!
I believe the answer is:
CRS("+proj=tmerc +lat_0=31.7343936111111 +lon_0=35.2045169444445 +k=1.0000067 +x_0=219529.584 +y_0=626907.39 +ellps=GRS80 +towgs84=-24.002400,-17.103200,-17.844400,-0.330090,-1.852690,1.669690,5.424800 +units=m +no_defs")
Yes?

Keren

Keren Raiter

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May 22, 2019, 6:57:43 AM5/22/19
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Thanks again Michael,

I wrote my last email before I saw your reply. The definition you provided today is similar but slightly different - it has a -0.33077 instead of a -0.330090. I'll use that one from now.
You wrote that working with ITM can be frustrating - any opinions on if working with ITM on ArcGIS is more or less accurate than in R?

Keren


Dr. Keren Raiter
Postdoctoral Research Fellow

Risk Management Ecology Lab

Department of Ecology, Evolution and Behavior

Hebrew University of Jerusalem


Michael Dorman

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May 22, 2019, 7:05:54 AM5/22/19
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Hi Keren,

Accuracy only depends on the CRS definition you use. In principle it doesn't matter if you use R, ArcGIS or any other software, the results will be exactly the same as long as the CRS definition is the same. 

Personally I think that working with this kind of transformations in R has the advantage that everything is transparent. With R, you are forced to tell the computer exactly what you want to do. 

In ArcGIS, or other graphical GIS software, many things happen automatically behind the scenes (such as "on the fly" reprojection), and if you simply trust the software without looking into details this can lead to wrong results. 

Best regards,

Michael

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Keren Raiter

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May 22, 2019, 8:50:20 AM5/22/19
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Many thanks once again. I completely agree with you. 



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