ShapeLibForESP32

• A library to read/write ESRI Shapefiles.
• ESP32 port of OSGEO/shapelib (from the commit 36106c2).
• WIP. We need testers. So far, it has only been tested on ESP32-S2 and ESP32-S3.
• SD library is used for storing and reading from SHP files.
• Even though the original C sources were converted to C++ for easy interfacing with the SD library, API is still C-ish.

Why?

• There are so many possible scenarios. For instance, you create polygons on QGIS or ArcGIS. Save your GIS layer to an SD card. Assume your board is equipped with a GPS receiver. You can program your board to achieve tasks based on the GPS position data. Do something in polygon A and do another thing in polygon B, etc., or create and store shapefiles on your SD card based on your position data from the GPS receiver. Then, open the stored shapefile on QGIS or ArcGIS for further analysis.

Example code 1

The example here contains 8 polygons and two data fields in the attribute table.

• Read shape and dbf files from SD card.
• Read and display info
• List lat and lon for polygon vertices
• List values of the attribute table

#include "shapefil.hpp"
#include "SD.h"

void setup() {
  Serial.begin(115200);

  if (!SD.begin()) {
    Serial.println("Card Mount Failed");
    return;
  }

  SHPsetFileSystem(SD);

  SHPHandle hSHP = SHPOpen("/regions/regions.shp", "r");
  DBFHandle hDBF = DBFOpen("/regions/regions.dbf", "r");
  if (hSHP == NULL || hDBF == NULL) {
    Serial.println("Failed to open shapefile or DBF file!");
    return;
  }

  // Get the number of entities and the type in the SHP file
  int nEntitiesSHP, nShapeType;
  SHPGetInfo(hSHP, &nEntitiesSHP, &nShapeType, NULL, NULL);
  Serial.printf("Shapefile: %d entities, Type: %d\n", nEntitiesSHP, nShapeType);

  // Get the number of records in the DBF file
  int nEntitiesDBF = DBFGetRecordCount(hDBF);
  Serial.printf("DBF file: %d records\n", nEntitiesDBF);

  // List field names
  int nFields = DBFGetFieldCount(hDBF);
  int iWidth, iDecimals;
  Serial.println("Field names:");
  for (int iField = 0; iField < nFields; ++iField) {
    char szFieldName[12];
    DBFGetFieldInfo(hDBF, iField, szFieldName, &iWidth, &iDecimals);
    Serial.printf("  Field %d: %s\n", iField, szFieldName);
  }

  // Read data from both files
  for (int iEntity = 0; iEntity < nEntitiesSHP; ++iEntity) {
    SHPObject* shp = SHPReadObject(hSHP, iEntity);
    Serial.printf("Entity %d has %d vertices:\n", iEntity, shp->nVertices);

    for (int iVertex = 0; iVertex < shp->nVertices; ++iVertex) {
      Serial.printf("  lon: %f, lat: %f\n", shp->padfX[iVertex], shp->padfY[iVertex]);
    }

    Serial.println("Attributes:");
    for (int iField = 0; iField < DBFGetFieldCount(hDBF); ++iField) {
      const char* value = DBFReadStringAttribute(hDBF, iEntity, iField);
      Serial.printf("  Field %d: %s\n", iField, value ? value : "NULL");
    }

    SHPDestroyObject(shp);
  }

  SHPClose(hSHP);
  DBFClose(hDBF);
}

void loop() {}

Example code 2

This example demonstrates working with a Shapefile and a corresponding DBF file stored on the SD card:

• Create or open a shapefile and corresponding DBF file on the SD card.
• Write a polygon (with 4 vertices) to the shapefile.
• Create a test field in the DBF file and write a value to the attribute table.
• Read and display the shapefile's geometry and attribute data.
• Display the polygon vertices' latitude and longitude (coordinates).
• Write test values to the attribute table.

#include "shapefil.hpp"
#include "SD.h"

void setup() {
  Serial.begin(115200);
  
  delay(1000);

  if (!SD.begin()) {
    Serial.println("Card Mount Failed");
    return;
  }

  SHPsetFileSystem(SD);
  
  const char *filename = "/p1.shp";
  const char *dbfFilename = "/p1.dbf";

  File file = SD.open(filename);
  if(!file) {
    file.close();
    Serial.println("File doesn't exist. Let's create it first!");
    Serial.println("Creating file...");
    SHPHandle hSHP = SHPCreate(filename, SHPT_POLYGON);

    if (hSHP == nullptr) {
      Serial.println("Failed to create SHP file!");
      return;
    } else {
      Serial.println("Shapefile created successfully!");
    }

    SHPClose(hSHP);

    // Create corresponding DBF file
    DBFHandle hDBF = DBFCreate(dbfFilename);
    if (hDBF == nullptr) {
      Serial.println("Failed to create DBF file!");
      return;
    } else {
      Serial.println("DBF file created successfully!");
    }

    // Add a test field to the DBF file
    if (DBFAddField(hDBF, "TestField", FTString, 20, 0) == -1) {
      Serial.println("Failed to add field to DBF file!");
      DBFClose(hDBF);
      return;
    }

    DBFClose(hDBF);
  } else {
    file.close();
    Serial.println("Using existing files...");
  }

  delay(1000);
  
  SHPHandle hSHP = SHPOpen(filename, "r+");
  DBFHandle hDBF = DBFOpen(dbfFilename, "r+");
  if (hSHP == nullptr || hDBF == nullptr) {
      Serial.println("Failed to open SHP or DBF file!");
      return;
  }

  int nShapeType;
  SHPGetInfo(hSHP, NULL, &nShapeType, NULL, NULL);
  Serial.println(nShapeType);

  // If the file is empty, set a type
  if (nShapeType == SHPT_NULL) {
      nShapeType = SHPT_POLYGON;
  }

  /* -------------------------------------------------------------------- */
  /*      Define example data.                                            */
  /* -------------------------------------------------------------------- */
  const int nVertices = 4; // Number of vertices
  double padfX[4] = {0.0, 10.0, 10.0, 0.0}; // X coordinates
  double padfY[4] = {0.0, 0.0, 10.0, 10.0}; // Y coordinates
  int panParts[1] = {0}; // Part start positions (for single-part polygon)

  /* -------------------------------------------------------------------- */
  /*      Create Shapefile object.                                        */
  /* -------------------------------------------------------------------- */
  SHPObject *psObject = SHPCreateObject(
      nShapeType, -1, 1, panParts, NULL, nVertices, padfX, padfY, NULL, NULL);
  if (psObject == nullptr) {
      Serial.printf("Failed to create Shapefile object.\n");
      SHPClose(hSHP);
      DBFClose(hDBF);
      return;
  }

  /* -------------------------------------------------------------------- */
  /*      Write to the Shapefile.                                         */
  /* -------------------------------------------------------------------- */
  Serial.println("Writing to disk...");
  if (SHPWriteObject(hSHP, -1, psObject) < 0) {
      Serial.printf("Failed to write to Shapefile.\n");
      SHPDestroyObject(psObject);
      SHPClose(hSHP);
      DBFClose(hDBF);
      return;
  }

  /* -------------------------------------------------------------------- */
  /*      Write data to the attribute table.                              */
  /* -------------------------------------------------------------------- */
  const char *testValue = "TestValue";
  if (!DBFWriteStringAttribute(hDBF, 0, 0, testValue)) { // Write to the 0th record
      Serial.println("Failed to write attribute to DBF file!");
  } else {
      Serial.println("Attribute written successfully!");
  }

  /* -------------------------------------------------------------------- */
  /*      Cleanup and exit.                                               */
  /* -------------------------------------------------------------------- */
  SHPDestroyObject(psObject);
  SHPClose(hSHP);
  DBFClose(hDBF);

  Serial.printf("Shapefile and DBF successfully written: %s\n", filename);
}

void loop() {}