[gdal-dev] Displaying vector files
Hi all, I am writing an application to load vector maps/shape files using gdal/ogr and display them onto a gui designed using Qt. I am new to dealing with vector files, I am not able to decide how to render them on GUI. Few approaches that come to my mind are: - To convert vector files to raster and display them as raster.. - To draw each shape in vector file one by one (i dont know how to do this, I dont even know whether it would be even possible this using GDAL/OGR, or how complex this would be because in my case vector files can be very complex) The decision how to render vector files is very important for me, because after displaying vector files i need to support some advanced features like projection change, interactive selection, Geo-referencing etc. Can any one who has worked on vector/gis stuff, tell me how this is usually done and what Qt widget is used for displaying such data. Thanks, Akshay gupta ___ gdal-dev mailing list gdal-dev@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/gdal-dev
Re: [gdal-dev] GDAL Tiling
I am presently using -srcwin for copying AOI to a different file. does -projwin have any advantage over -srcwin? Akhy On Wed, Mar 28, 2012 at 5:29 PM, Jay L. jzl5...@psu.edu wrote: Akshay, 1) An AOI can be created using the -projwin option in gdal_translate. You can use that option when creating a new raster with a new tiles size. 2) Using the Python bindings it is possible to read a segment of a raster into memory without allocating memory. I am unsure using another other language. Jay On Wed, Mar 28, 2012 at 5:16 AM, Mateusz Loskot mate...@loskot.netwrote: On 28 March 2012 07:45, akshay gupta akshaygupta...@gmail.com wrote: 2) When I read an image through ReadBlock() i had to allocate some memory and pass it in the function. Is there some way that i get the image data stored in GDALRasterBlock directly without passing my own allocated memory. http://www.gdal.org/classGDALRasterBlock.html#_details In normal situations applications do not interact directly with the GDALRasterBlock - instead it it utilized by the RasterIO() interfaces to implement caching Best regards, -- Mateusz Loskot, http://mateusz.loskot.net ___ gdal-dev mailing list gdal-dev@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/gdal-dev
Re: [gdal-dev] GDAL Tiling
Thanks Jay and Chaitanya, your comments helped a lot. I have few more doubts, these may be trivial but since i am new to GDAL i want to confirm. 1) Is it possible to cut a portion(AOI) of image in any format and store it as tiled GTiff. Cos i want to create multiple copied of image data as i keep editing them with different enhancements. and i want all the copies to be readily accessible in the form of tiles so that ram don't fill up too much. 2) When I read an image through ReadBlock() i had to allocate some memory and pass it in the function. Is there some way that i get the image data stored in GDALRasterBlock directly without passing my own allocated memory. Cos with this I would not have to write the buffer back using the WriteBlock(), and I can direclty change the block data improving the memory utilization. Thanks again, Akhy Hückelheim On Wed, Mar 28, 2012 at 12:20 AM, Jay L. jzl5...@psu.edu wrote: For a geotiff I would use the following to change block size. gdal_translate -of GTiff -co TILED=YES -co BLOCKXSIZE=256 -co BLOCKYSIZE=256 input output Replace 256with whatever integer you want. I realize that this is outside of your program, but it looks like you are going to need to modify the input data pre-processing. Jay On Tue, Mar 27, 2012 at 11:14 AM, akshay gupta akshaygupta...@gmail.comwrote: Hi, I have few questions regarding GDAL tiling and overviews. 1) Is there any In build direct function in GDAL from where i can set the size of the tiles(raster block size). 2)I an facing an strange situation. I have an TIFF image, and I am trying to read it block by block using ReadBlock(). When i read block from the band of the original dataset(GDALDataset I get when i call GDALOpen() ), I get a tile which is of size Width X 1 but if i create overviews and then call ReadBlock() on the band extracted from the first overview i get square tiles(Blocks). Can any body tell me why is this happening, Is there any way of getting square tiles of same size irrespective of whether i call ReadBlock() on original Dataset or on the overview level. Thanks and regards, Akhy Hückelheim ___ gdal-dev mailing list gdal-dev@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/gdal-dev ___ gdal-dev mailing list gdal-dev@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/gdal-dev
[gdal-dev] GDAL Tiling
Hi, I have few questions regarding GDAL tiling and overviews. 1) Is there any In build direct function in GDAL from where i can set the size of the tiles(raster block size). 2)I an facing an strange situation. I have an TIFF image, and I am trying to read it block by block using ReadBlock(). When i read block from the band of the original dataset(GDALDataset I get when i call GDALOpen() ), I get a tile which is of size Width X 1 but if i create overviews and then call ReadBlock() on the band extracted from the first overview i get square tiles(Blocks). Can any body tell me why is this happening, Is there any way of getting square tiles of same size irrespective of whether i call ReadBlock() on original Dataset or on the overview level. Thanks and regards, Akhy Hückelheim ___ gdal-dev mailing list gdal-dev@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/gdal-dev
Re: [gdal-dev] GDAL Tiling
Thanks for your quick reply, I dont want to use GDALRasterIO, I dont want to allocate memory of size equal that of image or ROI, i want to make use of tiling as much as possible. Can you provide more detail on how to create tiles tiff files by default. Akhy On Tue, Mar 27, 2012 at 9:30 PM, Chaitanya kumar CH chaitanya...@gmail.comwrote: CKYSIZE [1]. 2) You can read the raster any way you want using the GDALR ___ gdal-dev mailing list gdal-dev@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/gdal-dev
[gdal-dev] Saving shape files in GDAL/OGR
Hi, I have a loaded an raster image using GDAL, and i want to provide a drawing tool using which user can draw an irregular shape on the raster image and then save the shape and the enclosing pixels in a vector format for future use. Can any one tell me how to do this in GDAL/OGR? Thanks and regards, Akhy Huckelheim ___ gdal-dev mailing list gdal-dev@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/gdal-dev
[gdal-dev] caching in gdal
Hi all, How exactly does caching work in gdal. If I have 2 or more images opened simultaneously in gdal, does gdal consider the tiles(or scanlines) belonging to different images separately or does it keeps a common set, can any body explain how it is done in gdal. Thanks and regards, Akshay ___ gdal-dev mailing list gdal-dev@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/gdal-dev
