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Displaying sectional Geo-Tiffs with different projections

#1

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We’re having issues displaying the Geo-Tiffs in the right locations in Map Suite.
The projection information is included in the zip files for the Geo-Tiffs but we can’t translate into Map Suite effectively.

#2

Hi,

This issue is not a bug, it is caused by your incorrect projection text. You can build the correct projection text with following steps:

  1. Find the projection document in each zip file, it’s a htm file such as “Cape Lisburne SEC 51.htm”:
    a. You can get the projection name for example “Lambert Conformal Conic” and the datum information for example “North American Datum of 1983”.
    b. You can search the projection text with the information from http://spatialreference.org
    For example:
    b.1. Search the “Lambert Conformal Conic”:

You can click “SR-ORG:29” and download .prj file, this file provides “Lambert Conformal Conic” projection text format.

b.2. Search the “North American Datum of 1983”

You can click “SR-ORG:25” (or 23, 24) and download .prj file, this file provides “1983” datum parameters.

  1. Get the correct projection text:
    a. Some base projection information can be got from “Cape Lisburne SEC 51.htm”, such as:
    Standard_Parallel: 65.33333333333333
    Standard_Parallel: 70.66666666666667
    Longitude_of_Central_Meridian: -164.75
    Latitude_of_Projection_Origin: 70.3333333333
    False_Easting: 0.000000
    False_Northing: 0.000000

b. Open “SR-ORG:29” .prj file and replace these parameters as following:
1st Standard_Parallel: standard_parallel_1
2nd Standard_Parallel: standard_parallel_2
Longitude_of_Central_Meridian: central_meridian
Latitude_of_Projection_Origin: latitude_of_origin
False_Easting: false_easting
False_Northing: false_northing

c. Replace “GEOGCS”, “DATUM”, “SPHEROID” and “PRIMEM” parameters with the text from “SR-ORG:25” .prj file.

d. Get the final projection text : PROJCS[“WGC 84 / WRF Lambert”,GEOGCS[“GCS_North_American_1983”,DATUM[“D_North_American_1983”,SPHEROID[“GRS_1980”,6378137.0,298.257222101]],PRIMEM[“Greenwich”,0.0],UNIT[“Degree”,0.017453292519943295]],PROJECTION[“Lambert_Conformal_Conic”],PARAMETER[“central_meridian”, -164.75],PARAMETER[“latitude_of_origin”,70.3333333333],PARAMETER[“standard_parallel_1”,65.33333333333333],PARAMETER[“false_easting”,0.0],PARAMETER[“false_northing”,0.0],PARAMETER[“standard_parallel_2”,70.66666666666667],UNIT[“m”,1.0]]

  1. Use “Proj4Projection” object to convert the correct project to WGS84 as following statements:
    var prj = File.ReadAllText(@"…\AppData\new29.prj");
    var projection = new Proj4Projection(Proj4Projection.ConvertPrjToProj4(prj),
    Proj4Projection.GetWgs84ParametersString());
    projection.Open();

  2. You can display the .tiff file to correct position, as following snapshot:

    Pasted image780×590 128 KB

You can get the sample from https://ap.thinkgeo.com:5001/sharing/msrfHPYS8 , please have a try. If you have any questions, please let me know.

Thanks,

#3

From the customer:

“My issue is a little more complex in that I want to display two contiguous sectional maps so that they appear to be one map.
In order to do this, the maps have to be edited to remove the legend area to the left of the map while preserving the geo info.
I found a third party application that allows me to do this (QGIS Desktop). When I edit the maps with this application, they are rendered as one map as I expect.
When I render the two edited maps in ThinkGeo, they overlap.”

#4

Hi,

Thanks for the further information.

Actually, each of tiff files has its self’s projection text, if you use the same projection maybe they will overlap.

So you have to provide different projection information for each tiff file following above replying steps.

I have made serval .prj files for a part of tiff files, please download them here:
prj.zip (8.7 KB)

There is a sample which is how to merge multiple tiff files to one map, you can download it from https://ap.thinkgeo.com:5001/sharing/tEo7Q6qxR .

Please notice, our solution is adjust the image order to make map cover white area. But if you edit the tile, please make sure you only change white area to transparent but don’t directly cut the white area, or if the utility you used can modify the self-contained bounding box after edit cut this area is OK, which can make sure the images are rendered in correct position.

Pasted image786×562 296 KB

Thanks,