How to Use gdal for re-sample images

When writing a re-sample image, you can use gdal to read and write the image, and then write the re-sample algorithm (nearest pixel method, bilinear interpolation method, cubic convolution method, etc) [I will write an article to illustrate the principle of this sampling algorithm when I have time] Write the calculation result into the image for implementation.

In the gdal algorithm, five sampling algorithms are provided, which are defined as follows (46 rows of location gdalwarper. h ):

/*! Warp Resampling Algorithm */typedef enum {  /*! Nearest neighbour (select on one input pixel) */ GRA_NearestNeighbour=0,  /*! Bilinear (2x2 kernel) */                         GRA_Bilinear=1,  /*! Cubic Convolution Approximation (4x4 kernel) */  GRA_Cubic=2,  /*! Cubic B-Spline Approximation (4x4 kernel) */     GRA_CubicSpline=3,  /*! Lanczos windowed sinc interpolation (6x6 kernel) */ GRA_Lanczos=4} GDALResampleAlg;

View the source code of gdalwarp and find that warp is very powerful and can be used for projection conversion, re-projection, projection definition, re-sampling, Mosaic, geometric correction and image registration. In a word, it is very good and powerful. Next let's take a look at a little bit of it. Use warp to write a re-sampling interface. The Code is as follows:

/*** Re-sampling function (gdal) * @ Param pszsrcfile input file path * @ Param pszoutfile the path to the result image written * @ Param fresx x conversion sampling ratio, the default size is 1.0. If the image is larger than 1 and smaller than 1, the image is reduced * @ Param fresy y conversion sampling ratio. The default size is 1.0 * @ Param nresamplemode. There are five sampling modes, for details, see gdalresamplealg definition. The default value is bilinear interpolation * @ Param pextent sampling range. If it is null, it indicates calculating the sample band number specified by the full graph * @ Param pbandindex, null indicates the number of bands sampled in all bands * @ Param pbandcount, Which is used together with pbandindex, number of sample bands * @ Param pszformat format of the result image written * @ Param pProgress progress bar pointer * @ RET 0 is returned if urn is successful. Otherwise, it is another value */INT resamplegdal, int * pbandindex, int * pbandcount, const char * pszformat, lt_progress * pProgress) {If (pProgress! = NULL) {pProgress-> setprogresscaption ("weight??? "); PProgress-> setprogresstip (" positive? In? Hold? OK??? Like ?... ");} Gdalallregister (); gdaldataset * pdsrc = (gdaldataset *) gdalopen (pszsrcfile, ga_readonly); If (pdsrc = NULL) {If (pProgress! = NULL) pProgress-> setprogresstip ("? OK?? Text?? No? Save? At ?,? Or? By?? Ge?? No? By? Support? Hold ?!? "); Return re_nofile;} gdaldriver * pdriver = getgdaldrivermanager ()-> getdriverbyname (pszformat); If (pdriver = NULL) {If (pProgress! = NULL) pProgress-> setprogresstip ("no? Yes? Create??? Ge??? Text? Pieces ?!? "); Gdalclose (gdaldataseth) pdsrc); Return re_createfile;} int ibandcount = pdsrc-> getrastercount (); string strwkt = pdsrc-> getprojectionref (); gdaldatatype datatype = pdsrc-> getrasterband (1)-> getrasterdatatype (); double dgeotrans [6] = {0}; pdsrc-> getgeotransform (dgeotrans); int inewbandcount = ibandcount; if (pbandindex! = NULL & pbandcount! = NULL) {int imaxbandindex = pbandindex [0]; // query? Outbound? Most? Big?? Poo? Segment? Suo? Introduction? Order?? For (INT I = 1; I <* pbandcount; I ++) {If (imaxbandindex <pbandindex [I]) imaxbandindex = pbandindex [I];} If (imaxbandindex> ibandcount) {If (pProgress! = NULL) pProgress-> setprogresstip ("? OK?? Poo? Segment? Order?? Super?? Figure? Like?? Poo? Segment? Number ?,? Please? Check? Check? Lost? Incoming? Parameter? Number ?!? "); Gdalclose (gdaldataseth) pdsrc); Return re_paramerror;} inewbandcount = * pbandcount;} lt_envelope enextent; enextent. settonull (); If (pextent = NULL) // All? Figure??? {Double dprj [4] = {0}; // x1, x2, Y1, Y2 imagerowcol2projection (dgeotrans, 0, 0, dprj [0], dprj [2]); imagerowcol2projection (dgeotrans, pdsrc-> getrasterxsize (), pdsrc-> getrasterysize (), dprj [1], dprj [3]); enextent. init (dprj [0], dprj [1], dprj [2], dprj [3]); pextent = & enextent ;} dgeotrans [0] = pextent-> getminx (); dgeotrans [3] = pextent-> getmaxy (); dgeotrans [1] = dgeotrans [1]/fresx; dgeotrans [5] = dgeo Trans [5]/fresy; int inewwidth = static_cast <int> (pextent-> getmaxx ()-pextent-> getminx ()/ABS (dgeotrans [1]) + 0.5); int inewheight = static_cast <int> (pextent-> getmaxx ()-pextent-> getminx ()/ABS (dgeotrans [5]) + 0.5 )); gdaldataset * pddst = pdriver-> Create (pszoutfile, inewwidth, inewheight, inewbandcount, ype, null); If (pddst = NULL) {If (pProgress! = NULL) pProgress-> setprogresstip ("?? Lost? Outbound? Text?? Lost? Failed ?!? "); Gdalclose (gdaldataseth) pdsrc); Return re_createfile;} pddst-> setprojection (strwkt. c_str (); pddst-> setgeotransform (dgeotrans); gdalresamplealg eresample = (gdalresamplealg) nresamplemode; If (pProgress! = NULL) {pProgress-> setprogresstip ("positive? In? Hold? OK??? Like ?... "); PProgress-> setprogresstotalstep (inewbandcount * inewheight);} int * psrcband = NULL; int * pdstband = NULL; int ibandsize = 0; If (pbandindex! = NULL & pbandcount! = NULL) {ibandsize = * pbandcount; psrcband = new int [ibandsize]; pdstband = new int [ibandsize]; for (INT I = 0; I <ibandsize; I ++) {psrcband [I] = pbandindex [I]; pdstband [I] = I + 1 ;}} else {ibandsize = ibandcount; psrcband = new int [ibandsize]; pdstband = new int [ibandsize]; for (INT I = 0; I <ibandsize; I ++) {psrcband [I] = I + 1; pdstband [I] = I + 1 ;}} void * htransformarg = NULL, * hgenimupljarg = NULL; Htransformarg = hgenimupljarg = gdalcreategenimgprojtransformer2 (gdaldataseth) pdsrc, (gdaldataseth) pddst, null); If (htransformarg = NULL) {If (pProgress! = NULL) pProgress-> setprogresstip ("? Change? Parameter? Number? Error? Error ?!? "); Gdalclose (gdaldataseth) pdsrc); gdalclose (gdaldataseth) pddst); Return re_paramerror;} specify pfntransformer = conditions; gdalwarpoptions * PSWO = gdalcreatewarpoptions (); PSWO-> papszwarpoptions = cslduplicate (null); PSWO-> eworkingdatatype = datatype; PSWO-> eresamplealg = eresample; PSWO-> hsrcds = (gdaldataseth) pdsrc; PSWO-> hdstds = (gdaldataseth) pddst; PSWO-> pfnt Ransformer = pfntransformer; PSWO-> ptransformerarg = htransformarg; PSWO-> pfnprogress = gdalprogress; PSWO-> pprogressarg = pProgress; PSWO-> nbandcount = inewbandcount; PSWO-> pansrcbands = (int *) cplmalloc (inewbandcount * sizeof (INT); PSWO-> pandstbands = (int *) cplmalloc (inewbandcount * sizeof (INT )); for (INT I = 0; I <inewbandcount; I ++) {PSWO-> pansrcbands [I] = psrcband [I]; PSWO-> pandstbands [I] = PDS Tband [I];} release (psrcband); release (pdstband); gdalwarpoperation owo; If (owo. initialize (PSWO )! = Ce_none) {If (pProgress! = NULL) pProgress-> setprogresstip ("? Change? Parameter? Number? Error? Error ?!? "); Gdalclose (gdaldataseth) pdsrc); gdalclose (gdaldataseth) pddst); Return re_paramerror;} owo. chunkandwarpimage (0, 0, inewwidth, inewheight); values (PSWO-> ptransformerarg); values (PSWO); gdalclose (gdaldataseth) pdsrc); gdalclose (gdaldataseth) pddst ); if (pProgress! = NULL) pProgress-> setprogresstip ("weight???? ?!? "); Return re_success ;}

PS: When I use Windows Live writer to write a blog and use the vspaste plug-in to paste the code, I find that I will add "?" after the Chinese characters. No. I'm too lazy to modify it. Let's take a look!