Hi Rob, 1) whether transparency or alpha channels are supported
Yes. 2) any realistic resolution or image size constraints The limit is GDAL and the resources of you PC. 3) is indexed or RGB(A) preferred? This depends on your data. Optimal encoding of data is highly related to the statistical properties of the data. Indexing is better for maps with large uni-color areas. RGB and thus JPEG is better for maps with a high level of variation in color. 4) whether speific DATUM specification enjoy better or worse integration/support in the program: NAD27, WGS84, UTM, etc...since a LOT of my availble images are only available in old NAD27, yet I have to make them work in a WGS84 world. The datum of a map is just an offset. Map datums are NAD27 are WGS84. UTM is not a datum. It is a projection. QLGT can handle all Cartesian projections. But everything else won't work e.g. Lambert projections as used in fight charts. 5) MINIMUM geotiff tags that must be present Everything GDAL needs. You best use gdalinfo on your file to see if it is understood by GDAL 6) a better understanding of whether a tfw file can be used in lieu of manually georeferencing an image with control points tfw contains the rferencepoints of your map. But it lacks information about projection and datum. You have to find out these and use gdalwarp to create a real GeoTiff. > > Another thing that should really exist, if it doesn't already, is an > environment variable to control debug output of all the behind-the-scenes > gdal processing that goes on. a simple "cannot read xyz.tif?" error message > is not sufficient to figure out why the error occured. I am not aware of such an option in GDAL. but if you know better I am happy to accept a patch. > > Below is the listgeo and tiffinfo dump from a TIFF that works in the system, > followed by the dump of one that is not recognized. What is the key > difference that keeps the second one from working? The reference information is incomplete. I can not see information about the projection and the used Datum HTH Oliver > > WORKS!----------------------------------------------------------------- > $> listgeo ../WV/whitmer_ref.tif > TIFFReadDirectory: Warning, Unknown field with tag 42113 (0xa481) encountered. > Geotiff_Information: > Version: 1 > Key_Revision: 1.0 > Tagged_Information: > ModelTiepointTag (2,3): > 0 0 0 > -79.6250592 38.875044 0 > ModelPixelScaleTag (1,3): > 4.89618369e-05 4.89618369e-05 0 > End_Of_Tags. > Keyed_Information: > GTModelTypeGeoKey (Short,1): ModelTypeGeographic > GTRasterTypeGeoKey (Short,1): RasterPixelIsArea > GeographicTypeGeoKey (Short,1): User-Defined > GeogCitationGeoKey (Ascii,83): "GCS Name = unnamed ellipse|Datum = > unknown|Ellipsoid = unnamed|Primem = Greenwich|" > GeogGeodeticDatumGeoKey (Short,1): User-Defined > GeogAngularUnitsGeoKey (Short,1): Angular_Degree > GeogEllipsoidGeoKey (Short,1): User-Defined > GeogSemiMajorAxisGeoKey (Double,1): 6378206.4 > GeogInvFlatteningGeoKey (Double,1): 294.978698 > GeogPrimeMeridianLongGeoKey (Double,1): 0 > Unknown-2062 (Double,3): -8 160 176 > > End_Of_Keys. > End_Of_Geotiff. > > > Corner Coordinates: > Upper Left ( 79d37'30.21"W, 38d52'30.16"N) > Lower Left ( 79d37'30.21"W, 38d44'59.81"N) > Upper Right ( 79d29'58.98"W, 38d52'30.16"N) > Lower Right ( 79d29'58.98"W, 38d44'59.81"N) > Center ( 79d33'44.60"W, 38d48'44.98"N) > > $> tiffinfo ../WV/whitmer_ref.tif > TIFFReadDirectory: Warning, Unknown field with tag 33550 (0x830e) encountered. > TIFFReadDirectory: Warning, Unknown field with tag 33922 (0x8482) encountered. > TIFFReadDirectory: Warning, Unknown field with tag 34735 (0x87af) encountered. > TIFFReadDirectory: Warning, Unknown field with tag 34736 (0x87b0) encountered. > TIFFReadDirectory: Warning, Unknown field with tag 34737 (0x87b1) encountered. > TIFFReadDirectory: Warning, Unknown field with tag 42113 (0xa481) encountered. > TIFF Directory at offset 0x8 (8) > Image Width: 2560 Image Length: 2555 > Tile Width: 256 Tile Length: 256 > Bits/Sample: 8 > Sample Format: unsigned integer > Compression Scheme: AdobeDeflate > Photometric Interpretation: RGB color > Extra Samples: 1<assoc-alpha> > Samples/Pixel: 4 > Planar Configuration: single image plane > Tag 33550: 0.000049,0.000049,0.000000 > Tag 33922: 0.000000,0.000000,0.000000,-79.625059,38.875044,0.000000 > Tag 34735: > 1,1,0,11,1024,0,1,2,1025,0,1,1,2048,0,1,32767,2049,34737,83,0,2050,0,1,32767,2054,0,1,9102,2056,0,1,32767,2057,34736,1,0,2059,34736,1,1,2061,34736,1,2,2062,34736,3,3,0,0,0,0 > Tag 34736: > 6378206.400000,294.978698,0.000000,-8.000000,160.000000,176.000000 > Tag 34737: GCS Name = unnamed ellipse|Datum = unknown|Ellipsoid = > unnamed|Primem = Greenwich|| > Tag 42113: 255 > Predictor: none 1 (0x1) > TIFFReadDirectory: Warning, Unknown field with tag 42113 (0xa481) encountered. > TIFF Directory at offset 0x9b3b00 (10173184) > Subfile Type: reduced-resolution image (1 = 0x1) > Image Width: 1280 Image Length: 1278 > Tile Width: 128 Tile Length: 128 > Bits/Sample: 8 > Sample Format: unsigned integer > Compression Scheme: AdobeDeflate > Photometric Interpretation: RGB color > Extra Samples: 1<assoc-alpha> > Samples/Pixel: 4 > Planar Configuration: single image plane > Tag 42113: 255 > Predictor: none 1 (0x1) > TIFFReadDirectory: Warning, Unknown field with tag 42113 (0xa481) encountered. > TIFF Directory at offset 0x9b3ef6 (10174198) > Subfile Type: reduced-resolution image (1 = 0x1) > Image Width: 640 Image Length: 639 > Tile Width: 128 Tile Length: 128 > Bits/Sample: 8 > Sample Format: unsigned integer > Compression Scheme: AdobeDeflate > Photometric Interpretation: RGB color > Extra Samples: 1<assoc-alpha> > Samples/Pixel: 4 > Planar Configuration: single image plane > Tag 42113: 255 > Predictor: none 1 (0x1) > TIFFReadDirectory: Warning, Unknown field with tag 42113 (0xa481) encountered. > TIFF Directory at offset 0x9b4094 (10174612) > Subfile Type: reduced-resolution image (1 = 0x1) > Image Width: 320 Image Length: 320 > Tile Width: 128 Tile Length: 128 > Bits/Sample: 8 > Sample Format: unsigned integer > Compression Scheme: AdobeDeflate > Photometric Interpretation: RGB color > Extra Samples: 1<assoc-alpha> > Samples/Pixel: 4 > Planar Configuration: single image plane > Tag 42113: 255 > Predictor: none 1 (0x1) > TIFFReadDirectory: Warning, Unknown field with tag 42113 (0xa481) encountered. > TIFF Directory at offset 0x9b41b2 (10174898) > Subfile Type: reduced-resolution image (1 = 0x1) > Image Width: 160 Image Length: 160 > Tile Width: 128 Tile Length: 128 > Bits/Sample: 8 > Sample Format: unsigned integer > Compression Scheme: AdobeDeflate > Photometric Interpretation: RGB color > Extra Samples: 1<assoc-alpha> > Samples/Pixel: 4 > Planar Configuration: single image plane > Tag 42113: 255 > Predictor: none 1 (0x1) > TIFFReadDirectory: Warning, Unknown field with tag 42113 (0xa481) encountered. > TIFF Directory at offset 0x9b42a8 (10175144) > Subfile Type: reduced-resolution image (1 = 0x1) > Image Width: 80 Image Length: 80 > Tile Width: 128 Tile Length: 128 > Bits/Sample: 8 > Sample Format: unsigned integer > Compression Scheme: AdobeDeflate > Photometric Interpretation: RGB color > Extra Samples: 1<assoc-alpha> > Samples/Pixel: 4 > Planar Configuration: single image plane > Tag 42113: 255 > Predictor: none 1 (0x1) > > > > BROKEN! ---------------------------------------------------------------- > $> listgeo sigel_pa_ref.tif > Geotiff_Information: > Version: 1 > Key_Revision: 1.0 > Tagged_Information: > ModelTiepointTag (2,3): > 0 0 0 > 656801.062 4582106.46 0 > ModelPixelScaleTag (1,3): > 2.4384 2.4384 0 > End_Of_Tags. > Keyed_Information: > End_Of_Keys. > End_Of_Geotiff. > > > Corner Coordinates: > Upper Left ( 656801.062, 4582106.459) > Lower Left ( 656801.062, 4567993.000) > Upper Right ( 667576.352, 4582106.459) > Lower Right ( 667576.352, 4567993.000) > Center ( 662188.707, 4575049.730) > > $> tiffinfo sigel_pa_ref.tif > TIFFReadDirectory: Warning, Unknown field with tag 33550 (0x830e) encountered. > TIFFReadDirectory: Warning, Unknown field with tag 33922 (0x8482) encountered. > TIFF Directory at offset 0x8 (8) > Image Width: 4419 Image Length: 5788 > Resolution: 72, 72 pixels/inch > Bits/Sample: 8 > Sample Format: unsigned integer > Compression Scheme: None > Photometric Interpretation: RGB color > Extra Samples: 1<assoc-alpha> > Samples/Pixel: 4 > Rows/Strip: 1 > Planar Configuration: single image plane > DocumentName: /WD3TB/GPS/maps/CooksForest/sigel_pa_transparent.tif > Tag 33550: 2.438400,2.438400,0.000000 > Tag 33922: 0.000000,0.000000,0.000000,656801.062500,4582106.459200,0.000000 > > > > ------------------------------------------------------------------------------ > Slashdot TV. > Video for Nerds. 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