added observer x-distance test. (#97)

   EXPECT_NEAR(groundPt.z, 1.98000392e-01, 1e-8);

}

//Observer x position:

TEST_F(FrameIsdTest, X10_SlightlyOffCenter) {

   std::string key = "x_sensor_origin";

   std::string newValue = "10.0";

   isd.clearParams(key);

   isd.addParam(key,newValue);

   UsgsAstroFramePlugin frameCameraPlugin;

   csm::Model *model = frameCameraPlugin.constructModelFromISD(

         isd,

         "USGS_ASTRO_FRAME_SENSOR_MODEL");

   UsgsAstroFrameSensorModel* sensorModel = dynamic_cast<UsgsAstroFrameSensorModel *>(model);

   ASSERT_NE(sensorModel, nullptr);

   csm::ImageCoord imagePt(7.5, 6.5);

   csm::EcefCoord groundPt = sensorModel->imageToGround(imagePt, 0.0);

   EXPECT_NEAR(groundPt.x, 10.0, 1e-8);

   EXPECT_NEAR(groundPt.y, 0.0, 1e-8);

   EXPECT_NEAR(groundPt.z, 0.0, 1e-8);

}

TEST_F(FrameIsdTest, X1e9_SlightlyOffCenter) {

   std::string key = "x_sensor_origin";

   std::string newValue = "1000000000.0";

   isd.clearParams(key);

   isd.addParam(key,newValue);

   UsgsAstroFramePlugin frameCameraPlugin;

   csm::Model *model = frameCameraPlugin.constructModelFromISD(

         isd,

         "USGS_ASTRO_FRAME_SENSOR_MODEL");

   UsgsAstroFrameSensorModel* sensorModel = dynamic_cast<UsgsAstroFrameSensorModel *>(model);

   ASSERT_NE(sensorModel, nullptr);

   csm::ImageCoord imagePt(7.5, 6.5);

   csm::EcefCoord groundPt = sensorModel->imageToGround(imagePt, 0.0);

   //Note: In the following, the tolerance was increased due to the very large distance being tested (~6.68 AU).

   EXPECT_NEAR(groundPt.x, 3.99998400e+03, 1e-4);

   EXPECT_NEAR(groundPt.y, 0.0, 1e-4);

   EXPECT_NEAR(groundPt.z, 1.99999200e+06, 1e-4);

}

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