Add GDALLoadEsriCLRAsRAT() to load Esri .clr files as RAT

autotest/cpp/test_gdal.cpp

@@ -6575,4 +6575,28 @@ TEST_F(test_gdal, GDALRasterBand_HasConflictingMaskSources)
     }
 }
 
+TEST_F(test_gdal, GDALLoadEsriCLRAsRAT)
+{
+    auto poRAT = GDALLoadEsriCLRAsRAT(GDRIVERS_DATA_DIR "ehdr/int16_rat.clr");
+    ASSERT_TRUE(poRAT != nullptr);
+
+    ASSERT_EQ(poRAT->GetColumnCount(), 4);
+    ASSERT_EQ(poRAT->GetRowCount(), 25);
+
+    ASSERT_STREQ(poRAT->GetNameOfCol(0), "Value");
+    ASSERT_STREQ(poRAT->GetNameOfCol(1), "Red");
+    ASSERT_STREQ(poRAT->GetNameOfCol(2), "Green");
+    ASSERT_STREQ(poRAT->GetNameOfCol(3), "Blue");
+
+    ASSERT_EQ(poRAT->GetValueAsInt(0, 0), -500);
+    ASSERT_EQ(poRAT->GetValueAsInt(0, 1), 127);
+    ASSERT_EQ(poRAT->GetValueAsInt(0, 2), 40);
+    ASSERT_EQ(poRAT->GetValueAsInt(0, 3), 65);
+
+    ASSERT_EQ(poRAT->GetValueAsInt(24, 0), 2000);
+    ASSERT_EQ(poRAT->GetValueAsInt(24, 1), 145);
+    ASSERT_EQ(poRAT->GetValueAsInt(24, 2), 97);
+    ASSERT_EQ(poRAT->GetValueAsInt(24, 3), 47);
+}
+
 }  // namespace

frmts/raw/ehdrdataset.cpp

@@ -1532,54 +1532,26 @@ GDALDataset *EHdrDataset::Open(GDALOpenInfo *poOpenInfo, bool bFileSizeCheck)
 
     // Only read the .clr for byte, int16 or uint16 bands.
     if (nItemSize <= 2)
-        fp = VSIFOpenL(osCLRFilename.c_str(), "r");
-    else
-        fp = nullptr;
-
-    if (fp != nullptr)
     {
-        std::shared_ptr<GDALRasterAttributeTable> poRat(
-            new GDALDefaultRasterAttributeTable());
-        poRat->CreateColumn("Value", GFT_Integer, GFU_Generic);
-        poRat->CreateColumn("Red", GFT_Integer, GFU_Red);
-        poRat->CreateColumn("Green", GFT_Integer, GFU_Green);
-        poRat->CreateColumn("Blue", GFT_Integer, GFU_Blue);
-
-        poDS->m_poColorTable.reset(new GDALColorTable());
-
-        bool bHasFoundNonCTValues = false;
-        int nRatRow = 0;
-
-        while (true)
+        auto poRAT = GDALLoadEsriCLRAsRAT(osCLRFilename.c_str());
+        if (poRAT && poRAT->GetColumnCount() == 4)
         {
-            pszLine = CPLReadLineL(fp);
-            if (!pszLine)
-                break;
-
-            if (*pszLine == '#' || *pszLine == '!')
-                continue;
+            poDS->m_poColorTable = std::make_unique<GDALColorTable>();
 
-            char **papszValues =
-                CSLTokenizeString2(pszLine, "\t ", CSLT_HONOURSTRINGS);
+            bool bHasFoundNonCTValues = false;
 
-            if (CSLCount(papszValues) >= 4)
+            for (int iRow = 0; iRow < poRAT->GetRowCount(); ++iRow)
             {
-                const int nIndex = atoi(papszValues[0]);
-                poRat->SetValue(nRatRow, 0, nIndex);
-                poRat->SetValue(nRatRow, 1, atoi(papszValues[1]));
-                poRat->SetValue(nRatRow, 2, atoi(papszValues[2]));
-                poRat->SetValue(nRatRow, 3, atoi(papszValues[3]));
-                nRatRow++;
-
+                const int nIndex = poRAT->GetValueAsInt(iRow, 0);
                 if (nIndex >= 0 && nIndex < 65536)
                 {
                     const GDALColorEntry oEntry = {
-                        static_cast<short>(
-                            std::clamp(atoi(papszValues[1]), 0, 255)),  // Red
-                        static_cast<short>(
-                            std::clamp(atoi(papszValues[2]), 0, 255)),  // Green
-                        static_cast<short>(
-                            std::clamp(atoi(papszValues[3]), 0, 255)),  // Blue
+                        static_cast<short>(std::clamp(
+                            poRAT->GetValueAsInt(iRow, 1), 0, 255)),  // Red
+                        static_cast<short>(std::clamp(
+                            poRAT->GetValueAsInt(iRow, 2), 0, 255)),  // Green
+                        static_cast<short>(std::clamp(
+                            poRAT->GetValueAsInt(iRow, 3), 0, 255)),  // Blue
                         255};
 
                     poDS->m_poColorTable->SetColorEntry(nIndex, &oEntry);
@@ -1591,32 +1563,28 @@ GDALDataset *EHdrDataset::Open(GDALOpenInfo *poOpenInfo, bool bFileSizeCheck)
                     //   http://www.ngdc.noaa.gov/mgg/topo/elev/esri/clr/
                     // But, there's no way of representing them with GDAL color
                     // table model.
-                    if (!bHasFoundNonCTValues)
-                        CPLDebug("EHdr", "Ignoring color index : %d", nIndex);
+                    CPLDebug("EHdr", "Ignoring color index : %d", nIndex);
                     bHasFoundNonCTValues = true;
+                    break;
                 }
             }
 
-            CSLDestroy(papszValues);
-        }
-
-        CPL_IGNORE_RET_VAL(VSIFCloseL(fp));
+            if (bHasFoundNonCTValues)
+            {
+                poDS->m_poRAT.reset(poRAT.release());
+            }
 
-        if (bHasFoundNonCTValues)
-        {
-            poDS->m_poRAT.swap(poRat);
-        }
+            for (int i = 1; i <= poDS->nBands; i++)
+            {
+                EHdrRasterBand *poBand =
+                    cpl::down_cast<EHdrRasterBand *>(poDS->GetRasterBand(i));
+                poBand->m_poColorTable = poDS->m_poColorTable;
+                poBand->m_poRAT = poDS->m_poRAT;
+                poBand->SetColorInterpretation(GCI_PaletteIndex);
+            }
 
-        for (int i = 1; i <= poDS->nBands; i++)
-        {
-            EHdrRasterBand *poBand =
-                cpl::down_cast<EHdrRasterBand *>(poDS->GetRasterBand(i));
-            poBand->m_poColorTable = poDS->m_poColorTable;
-            poBand->m_poRAT = poDS->m_poRAT;
-            poBand->SetColorInterpretation(GCI_PaletteIndex);
+            poDS->bCLRDirty = false;
         }
-
-        poDS->bCLRDirty = false;
     }
 
     // Read statistics (.STX).

gcore/gdal_rat.cpp

@@ -27,6 +27,7 @@
 #include "cpl_error.h"
 #include "cpl_string.h"
 #include "cpl_vsi.h"
+#include "cpl_vsi_virtual.h"
 
 #ifdef __clang__
 #pragma clang diagnostic push
@@ -3421,3 +3422,55 @@ void CPL_STDCALL GDALRATRemoveStatistics(GDALRasterAttributeTableH hRAT)
 
     GDALRasterAttributeTable::FromHandle(hRAT)->RemoveStatistics();
 }
+
+/************************************************************************/
+/*                        GDALLoadEsriCLRAsRAT()                        */
+/************************************************************************/
+
+/**
+ * \brief Load a Esri .clr as a RAT.
+ *
+ * @param pszFilename .clr filename
+ *
+ * @return a new RAT, or nullptr in case of error.
+ *
+ * @since GDAL 3.14
+ */
+std::unique_ptr<GDALRasterAttributeTable>
+GDALLoadEsriCLRAsRAT(const char *pszFilename)
+{
+    auto fp = VSIFilesystemHandler::OpenStatic(pszFilename, "rb");
+    if (!fp)
+        return nullptr;
+
+    auto poRAT = std::make_unique<GDALDefaultRasterAttributeTable>();
+    poRAT->CreateColumn("Value", GFT_Integer, GFU_Generic);
+    poRAT->CreateColumn("Red", GFT_Integer, GFU_Red);
+    poRAT->CreateColumn("Green", GFT_Integer, GFU_Green);
+    poRAT->CreateColumn("Blue", GFT_Integer, GFU_Blue);
+
+    int nRatRow = 0;
+
+    constexpr int MAX_LINE_SIZE = 1000;  // Arbitary
+    while (const char *pszLine =
+               CPLReadLine2L(fp.get(), MAX_LINE_SIZE, nullptr))
+    {
+        if (*pszLine == '#' || *pszLine == '!')
+            continue;
+
+        const CPLStringList aosTokens(
+            CSLTokenizeString2(pszLine, "\t ", CSLT_HONOURSTRINGS));
+
+        if (aosTokens.size() >= 4)
+        {
+            const int nIndex = atoi(aosTokens[0]);
+            poRAT->SetValue(nRatRow, 0, nIndex);
+            poRAT->SetValue(nRatRow, 1, atoi(aosTokens[1]));
+            poRAT->SetValue(nRatRow, 2, atoi(aosTokens[2]));
+            poRAT->SetValue(nRatRow, 3, atoi(aosTokens[3]));
+            nRatRow++;
+        }
+    }
+
+    return poRAT;
+}

gcore/gdal_rat.h

@@ -586,4 +586,7 @@ class CPL_DLL GDALDefaultRasterAttributeTable : public GDALRasterAttributeTable
 std::unique_ptr<GDALRasterAttributeTable>
     CPL_DLL GDALLoadVATDBF(const char *pszFilename);
 
+std::unique_ptr<GDALRasterAttributeTable>
+    CPL_DLL GDALLoadEsriCLRAsRAT(const char *pszFilename);
+
 #endif /* ndef GDAL_RAT_H_INCLUDED */