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-rw-r--r--src/projections/nsper.cpp5
1 files changed, 5 insertions, 0 deletions
diff --git a/src/projections/nsper.cpp b/src/projections/nsper.cpp
index 059b9f71..852d0c98 100644
--- a/src/projections/nsper.cpp
+++ b/src/projections/nsper.cpp
@@ -4,6 +4,11 @@
#include "proj_internal.h"
#include <math.h>
+/* Note: EPSG Guidance 7-2 describes a Vertical Perspective method (EPSG::9838),
+ * that extends 'nsper' with ellipsoidal development, and a ellipsoidal height
+ * of topocentric origin for the projection plan.
+ */
+
namespace { // anonymous namespace
enum Mode {
N_POLE = 0,