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How can I map latitude/longitude to an FAA digital chart? Attached is a sample GEOTIFF. More specifically, how can I get a reference points from the digital data?

Once I can get reference points, I have no problem translating Pixel-Lat/Long. In my testing, I have been manually identifying the reference points to the the translation. This is a rather tedious process.

It looks like I just need a single lat/long-pixel-x/y mapping to derive them all from this data.

The GEOTIFF spec suggests the Model Tie Point is the key but the example in the spec does not match this data. -822739.829757951 -64249.12941973 does not give units not does it give offset from what?

In this chart the false origin is located at the Pixel coordinates (6521 3865) from the upper left corner.

Thanks

ExifTool Version Number         : 9.53
File Name                       : CF-19 WAC 43 South.tif
Directory                       : .
File Size                       : 47 MB
File Modification Date/Time     : 2013:03:15 10:45:54-04:00
File Access Date/Time           : 2014:02:28 13:45:59-05:00
File Inode Change Date/Time     : 2014:02:28 13:06:22-05:00
File Permissions                : rwxr-xr-x
File Type                       : TIFF
MIME Type                       : image/tiff
Exif Byte Order                 : Little-endian (Intel, II)
Image Width                     : 11888
Image Height                    : 4135
Bits Per Sample                 : 8
Compression                     : Uncompressed
Photometric Interpretation      : RGB Palette
Strip Offsets                   : (Binary data 286 bytes, use -b option to extract)
Samples Per Pixel               : 1
Rows Per Strip                  : 128
Strip Byte Counts               : (Binary data 262 bytes, use -b option to extract)
Planar Configuration            : Chunky
Color Map                       : (Binary data 1536 bytes, use -b option to extract)
Sample Format                   : Unsigned
Pixel Scale                     : 127.09668 127.09668 0
Model Tie Point                 : 0 0 0 -822739.829757951 -64249.12941973 0
GDAL Metadata                   : <GDALMetadata>.  <Item name="PyramidResamplingType" domain="ESRI">NEAREST</Item>.  <Item name="RepresentationType" sample="0">THEMATIC</Item>.  <Item name="STATISTICS_MINIMUM" sample="0">0</Item>.  <Item name="STATISTICS_MAXIMUM" sample="0">255</Item>.  <Item name="STATISTICS_MEAN" sample="0">108.47642098115</Item>.  <Item name="STATISTICS_STDDEV" sample="0">83.473159026412</Item>.</GDALMetadata>.
GDAL No Data                    : 256
Geo Tiff Version                : 1.1.0
GT Model Type                   : Projected
GT Raster Type                  : Pixel Is Area
GT Citation                     : PCS Name = CF-19 WAC
Geographic Type                 : NAD83
Geog Citation                   : GCS_North_American_1983
Geog Angular Units              : Angular Degree
Geog Semi Major Axis            : 6378137
Geog Inv Flattening             : 298.257222101
Projected CS Type               : User Defined
Projection                      : User Defined
Proj Coord Trans                : Lambert Conf Conic 2SP
Proj Linear Units               : Linear Meter
Proj Std Parallel 1             : 46.6666666666667
Proj Std Parallel 2             : 41.3333333333333
Proj False Origin Long          : -69
Proj False Origin Lat           : 44.41667
Proj False Origin Easting       : 0
Proj False Origin Northing      : 0
Image Size                      : 11888x4135
  • What GIS software and version are you using? – PolyGeo Mar 1 '14 at 7:27
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If you have QGIS, you can simply load the tif file as raster data. From the metadata, a custom CRS will automatically be created. For the New York map, this is:

+proj=lcc +lat_1=46.66666666666666 +lat_2=41.33333333333334 +lat_0=42.1 +lon_0=-72.83333333333333 +x_0=0 +y_0=0 +datum=NAD83 +units=m +no_defs:

enter image description here

Unfortunately, there was some error in handling lcc 2SP with different lat_0, lat_1 and lat_2. The latest version of GDAL and QGIS should be ok. On-the-fly-reprojecting is still an issue, so you better reproject the map to some other CRS.

The answer to this question should show you how to create the necessary custom CRS: How can I dynamically trim the informational border off of FAA sectional raster charts?

Doing the extraction manually will indeed be very tedious, because the pixels are projected to meters, while lat/lon are in degrees and therefore no affine transformation will be possible.

  • This is what I have been doing. 1. I identify 6 points on a lat/long box. Two of these are on the false origin latitude. The others are at the widest latitude/longitude coordinates. – Steve Smith Mar 1 '14 at 13:02
  • I added a ddegree grid to my picture. I doubt your method will respect the bended latitudes correctly. – AndreJ Mar 2 '14 at 7:35

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